Purpose: ⁶⁸Ga-DOTA-JR11 is an antagonist for somatostatin receptor used in neuroendocrine imaging. The purpose of this study is to compare ⁶⁸Ga-DOTA-JR11 and ⁶⁸Ga-DOTATATE PET/CT in patients with metastatic, well-differentiated neuroendocrine tumors. Methods: Patients with histologically-proven, metastatic and/or unresectable, well-differentiated neuroendocrine tumors were prospectively recruited in this study. They received an intravenous injection of ⁶⁸Ga-DOTATATE (4.0 ± 1.3 mCi) on the first day and ⁶⁸Ga-DOTA-JR11 (4.0 ± 1.4 mCi) on the second day. Whole-body PET/CT scans were performed at 40 to 60 minutes after injection on the same scanner. Physiologic uptake of normal organs, lesion numbers, and lesion uptake were compared. Results: Twenty-nine patients were prospectively enrolled in the study. The SUV_max of the spleen, renal cortex, adrenal glands, pituitary glands, stomach wall, normal liver parenchyma, small intestine, pancreas, and bone marrow were significantly lower on ⁶⁸Ga-DOTA-JR11 than on ⁶⁸Ga-DOTATATE PET/CT (P<0.001). ⁶⁸Ga-DOTA-JR11 detected significantly more liver lesions (539 vs. 356, P = 0.002), but fewer bone lesions (156 vs. 374, P = 0.031, Figure 3) than ⁶⁸Ga-DOTATATE. The tumor-to-background ratio of liver lesions was significantly higher on ⁶⁸Ga-DOTA-JR11 (7.6 ± 5.1 vs. 3.4 ± 2.0, P<0.001). ⁶⁸Ga-DOTA-JR11 and ⁶⁸Ga-DOTATATE PET/CT showed comparable results for primary tumors and lymph node metastases based on either patient-based or lesion-based comparison. Conclusion: ⁶⁸Ga-DOTA-JR11 performs better in the detection ability and TBR of liver metastases. However, ⁶⁸Ga-DOTATATE outperforms ⁶⁸Ga-DOTA-JR11 in the detection of bone metastases. The differential affinity of different metastatic sites provides key information for patient selection in imaging and peptide receptor radionuclide therapy.

Rationale: Lymphatic tracers can help visualize the lymphatic drainage patterns and sentinel nodes of individual prostate cancer patients. To determine the role of nuclear medicine, in particular the positional guidance of a SPECT/CT-based 3D imaging roadmap, in this process we studied to which extend fluorescence-guidance underestimated the number of target lesions. Methods: SPECT/CT imaging was performed after intraprostatic tracer administration of either ICG-^99mTc-nanocolloid (hybrid tracer group) or ^99mTc-nanocolloid to create a roadmap that depicted all sentinel nodes (SNs). Patients who received ^99mTc-nanocolloid were injected with "free" ICG immediately prior to surgery ("free" ICG group). Before unblinding, fluorescence-guidance was used for intraoperative SN identification. This was followed by extended pelvic lymph node dissection (ePLND). Following unblinding of the SPECT/CT images, the number of missed SN’s were recorded and their resection was pursued when the anatomy allowed. Results: Preoperative SPECT/CT revealed no differences in the SN identification rate between ICG-^99mTc-nanocolloid and ^99mTc-nanocolloid. However, fluorescence-guidance only allowed intraoperative removal of all SNs in 40% of patients in the hybrid tracer group and in 20% of patients in the "free" ICG group. Overall, 75.9% of the intraoperatively resected SNs in the hybrid tracer group and 51.8% of the SNs in the "free" ICG group were removed solely under fluorescence-guidance. During ePLND 22 additional SNs were resected (7 in the hybrid tracer group and 15 in the "free" ICG group). After unblinding 18 remaining SNs were identified (6 in the hybrid group and 12 in the "free" ICG group). In the "free" ICG group, ex vivo evaluation of the excised specimens revealed that 14 SNs removed under ePLND or after unblinding contained radioactivity but no fluorescence. Conclusion: The preoperative imaging roadmap provided by SPECT/CT enhanced the detection of prostate SNs in more ectopic locations in 17 of the 25 patients and the hybrid tracer ICG-^99mTc-nanocolloid was shown to outperform "free" ICG. Overall, fluorescence-guided pelvic nodal surgery underestimated the number of SNs in 60-80% of patients.

¹⁸F-PI-2620 is a positron emission tomography (PET) tracer with high binding affinity for aggregated tau, a key pathologic feature of Alzheimer’s disease (AD) and other neurodegenerative disorders. Preclinically, ¹⁸F-PI-2620 binds to both, 3R and 4R tau isoforms. The purpose of this first-in-human study was to evaluate the ability of ¹⁸F-PI-2620 to detect tau pathology in AD patients using PET imaging, as well as to assess its safety and tolerability of this new tau PET tracer. Methods: Participants with clinical diagnosis of probable AD and healthy controls (HC) underwent dynamic ¹⁸F-PI-2620 PET imaging for 180 min. ¹⁸F-PI-2620 binding was assessed visually and quantitatively using Distribution Volume Ratios (DVR) estimated from non-invasive tracer kinetics and standardized uptake value ratios (SUVR) measured at different time points post-injection (p.i.) with the cerebellar cortex as the reference region. Time-activity curves and SUVR were assessed in AD and HC, as well as DVR and SUVR correlations and effect size (Cohen’s d) over time. Results: ¹⁸F-PI-2620 showed peak brain uptake around 5 min p.i. and fast wash-out in non-target regions. In AD subjects, focal asymmetric uptake was evident in temporal and parietal lobes, precuneus, and posterior cingulate cortex. DVR and SUVR in these regions were significantly higher in AD compared to HC. Very low background signal was observed in HC. ¹⁸F-PI-2620 administration was safe and well tolerated. SUVR time activity curves in most regions and subjects achieved a secular equilibrium after 40 min p.i.. A strong correlation (R² > 0.93) was found between non-invasive DVR and SUVR for all imaging windows starting >30 min p.i.. Similar effect sizes between AD and HC groups were obtained across the different imaging windows. ¹⁸F-PI-2620 uptake in neocortical regions was significantly correlated with the degree of cognitive impairment. Conclusion: Initial clinical data obtained in AD and HC demonstrate the high image quality with excellent signal-to-noise of ¹⁸F-PI-2620 PET for imaging tau deposition in AD subjects. Non-invasive quantification using DVR and SUVR for 30 min imaging windows between 30-90 min p.i., e.g. 45-75 min, provides robust and significant discrimination between AD and HC subjects. ¹⁸F-PI-2620 uptake in expected regions is highly correlated to neurocognitive performance.

¹⁸F-PI-2620 is a next generation tau positron emission tomography (PET)-tracer that has demonstrated ability to image the spatial distribution of suspected tau pathology. The objective of this study was to assess the tracer biodistribution, dosimetry and quantitative methods of ¹⁸F-PI-2620 in the human brain. Full kinetic modelling approaches to quantify tau load were investigated. Non-invasive kinetic modeling approaches and semi-quantitative methods were evaluated against the full tracer kinetics. Finally, the reproducibility of PET measurements from test and retest scans was assessed. Methods: Three healthy controls (HC) and 4 Alzheimer disease (AD) subjects underwent two dynamic PET scans including arterial sampling. Distribution volume ratio (DVR) was estimated using full tracer kinetics (2 Tissue Compartment (2TC) models, Logan Graphical Analysis (LGA)) and non-invasive kinetic models (Non-Invasive Logan Graphical Analysis (NI-LGA) and the multilinear reference tissue model (MRTM2)). Standardized uptake value ratio (SUVR) was determined at different imaging windows after injection. Correlation between DVR and SUVR, effect size (Cohen’s d) and test-retest variability (TRV) were evaluated. Additionally, 6 HC subjects received one tracer administration and underwent whole-body PET for dosimetry calculation. Organ doses and the whole-body effective dose were calculated using OLINDA 2.0. Results: Strong correlation was found across different kinetic models (R2 >0.97) and between DVR(2TC) and SUVRs between 30 to 90 min with R2>0.95. Secular equilibrium was reached around 40 min post injection (p.i.) in most regions and subjects. The TRV and effect size for the SUVR across different regions was similar at 30-60 min (TRV=3.8%, d=3.80), 45-75 min (TRV=4.3%, d=3.77) and 60-90 min (TRV=4.9%, d=3.73) and increased at later time points. Elimination was via the hepatobiliary and urinary system. The whole-body effective dose was determined to be 33.3±2.1 μSv/MBq for an adult female and 33.1±1.4 μSv/MBq for an adult male with a 1.5 hour urinary bladder voiding interval. Conclusion: ¹⁸F-PI-2620 exhibits fast kinetics, suitable dosimetry and low TRV. DVR measured using the 2TC model with arterial sampling correlated strongly with DVR measured by NI-LGA, MRTM2 and SUVR. SUVR can be used for ¹⁸F-PI-2620 PET quantification of tau deposits avoiding arterial blood sampling. Static ¹⁸F-PI-2620 PET scans between 45-75min p.i. provide excellent quantification accuracy, large effect size and low TRV.

The purpose of this study was to assess the predictive and prognostic value of interim FDG PET (iPET) in evaluating early response to immuno-chemotherapy after two cycles (PET-2) in diffuse large B-cell lymphoma (DLBCL) by applying two different methods of interpretation: the Deauville visual five-point scale (5-PS) and a change in standardised uptake value by semi-quantitative evaluation. Methods: 145 patients with newly diagnosed DLBCL underwent pre-treatment PET (PET-0) and PET-2 assessment. PET-2 was classified according to both the visual 5-PS and percentage SUV changes (SUV). Receiver operating characteristic (ROC) analysis was performed to compare the accuracy of the two methods for predicting progression-free survival (PFS). Survival estimates, based on each method separately and combined, were calculated for iPET-positive (iPET+) and iPET-negative (iPET–) groups and compared. Results: Both with visual and SUV-based evaluations significant differences were found between the PFS of iPET– and iPET+ patient groups (p<0.001). Visually the best negative (NPV) and positive predictive value (PPV) occurred when iPET was defined as positive if Deauville score 4-5 (89% and 59%, respectively). Using the 66% SUV cut-off value, reported previously, NPV and PPV were 80 and 76%, respectively. SUV at 48.9% cut-off point, reported for the first time here, produced 100% specificity along with the highest sensitivity (24%). Visual and semi-quantitative SUV<48.9% assessment of each PET-2 gave the same PET-2 classification (positive or negative) in 70% (102/145) of all patients. This combined classification delivered NPV and PPV of 89% and 100% respectively, and all iPET+ patients failed to achieve or remain in remission. Conclusion: In this large consistently treated and assessed series of DLBCL, iPET had good prognostic value interpreted either visually or semi-quantitatively. We determined that the most effective SUV cut-off was at 48.9%, and that when combined with visual 5-PS assessment, a positive PET-2 was highly predictive of treatment failure.

Introduction: Aromatase inhibitors are the mainstay of hormonal therapy in estrogen receptor positive, postmenopausal breast cancer, although response rate is just over 50%. The goal of the present study was to validate and optimize positron emission tomography (PET) with ¹¹C-vorozole for measuring aromatase expression in postmenopausal breast cancer. Methods: Ten newly diagnosed, postmenopausal women with biopsy confirmed breast cancer were administered ¹¹C-vorozole intravenously and PET emission data collected between 40 – 90 minutes post-injection. Tracer injection and scanning were repeated 2 hours after ingestion of 2.5mg letrozole p.o. Mean and maximal standard uptake values and ratios to non-tumor tissue (SUVs, SUVRs) were calculated for tumor and non-tumor regions at baseline and after letrozole. Biopsy specimens from the same tumors were stained for aromatase using immunohistochemistry and evaluated for stain intensity and the percentage of immune-positive cells. Results: Seven of the 10 women (70%) demonstrated increased focal uptake of tracer (SUVR>1.1) coinciding with the mammographic location of the lesion. The other 3 women (30%) did not show increased uptake in the tumor (SUVR <1.0). All of the cases with SUVR above 1.1 had SUVs above 2.4 and there was no overlap in SUV between the two groups, with mean SUV in tumors overexpressing aromatase (SUVR>1.1) ranging from 2.47 to 13.6, while tumors not overexpressing aromatase (SUVR<1) ranged from 0.8 to 1.8. Pretreatment with letrozole reduced tracer uptake in the majority of subjects; although the %blocking varied across and within tumors. Tumors with high SUV in vivo also showed high staining intensity on IHC. Conclusion: PET with ¹¹C-vorozole is a useful technique for measuring aromatase expression in individual breast lesions, enabling a non-invasive quantitative measurement of baseline and post-treatment aromatase availability in primary tumors and metastatic lesions.

Numerous recent works highlight the limited utility of established tumor cell lines in recapitulating the heterogeneity of tumors in patients. More realistic preclinical cancer models are thought to be provided by transplantable, patient-derived tumor xenografts (PDX). Inter- and intra-tumor heterogeneity of PDX, however, present several challenges in developing optimal quantitative pipelines to assess response to therapy. The objective of this work was to develop and optimize image metrics of FDG-PET to assess response to combination docetaxel/carboplatin therapy in a co-clinical trial involving triple negative breast cancer (TNBC) PDX. We characterize the reproducibility of SUV metrics to assess response to therapy and optimize a preclinical PERCIST (µPERCIST) paradigm to complement clinical standards. Considerations in this effort included variability in tumor growth rate and tumor size; solid tumor vs. tumor heterogeneity and necrotic phenotype; and optimal selection of tumor slice versus whole tumor. A test-retest protocol was implemented to optimize the reproducibility of FDG-PET SUV thresholds, SUVpeak metrics, and µPERCIST parameters. In assessing response to therapy, FDG-PET imaging was performed at baseline and +4 days following therapy. The reproducibility, accuracy, variability, and performance of imaging metrics to assess response to therapy were determined. We defined an index—"Quantitative Response Assessment Score (QRAS)"—to integrate parameters of prediction and precision, and thus aid in selecting optimal image metrics of response to therapy. Our data suggests that a threshold value of 25% (SUV25) of SUVmax was highly reproducible (<9% variability). Concordance and reproducibility of µPERCIST were maximized at α=0.7 and β=2.8 and exhibited high correlation to SUV25 measures of tumor uptake. QRAS scores favor SUV25 followed by SUVP14 as optimal metrics of response to therapy. Additional studies are warranted to fully characterize the utility of SUV25 and µPERCIST SUVP14 as image metrics of response to therapy across a wide range of therapeutic regiments and PDX models.

Objectives: Lutetium-177 (¹⁷⁷Lu)-PSMA-617 (LuPSMA) is a radioligand with high affinity for prostate specific membrane antigen (PSMA) enabling targeted beta-irradiation of prostate cancer. We have previously reported favorable activity with low toxicity in a prospective phase II trial involving 30 men with metastatic castrate-resistant prostate cancer (mCRPC). We now report their longer-term outcomes including a 20 patient extension cohort and outcomes of subsequent systemic treatments following completion of trial therapy. Methods: 50 patients with PSMA-avid mCRPC who had progressed after standard therapies received up to 4 cycles of LuPSMA every 6 weeks. Endpoints included PSA response (PCWG2), toxicity (CTCAE v4.03), imaging response, patient-reported health-related quality of life (QoL), progression-free and overall survival. We also describe, as a novel finding, outcomes of men who subsequently progressed and had further systemic therapies, including LuPSMA. Results: 75 men were screened to identify 50 patients eligible for treatment. Adverse prognostic features of the cohort included short median PSA doubling time (2.3 months) and extensive prior treatment including prior docetaxel (84%), cabazitaxel (48%), and abiraterone and/or enzalutamide (90%). The mean administered radioactivity was 7.5 GBq/cycle. PSA decline ≥ 50% was achieved in 32 of 50 patients (64%, 95% CI 50-77%), including 22 patients (44%, 95% CI 30-59%) with ≥ 80% decrease. Of 27 patients with measurable soft tissue disease, 15 (56%) achieved an objective response by RECIST 1.1. The most common toxicities attributed to LuPSMA were self-limiting G1-2 dry mouth (66%), transient G1-2 nausea (48%), G3-4 thrombocytopenia (10%) and G3 anemia (10%). Brief pain inventory severity and interference scores decreased at all time points including at the 3 month follow-up with a decrease of -1.2 (95% CI -0.5 to -1.9, P = 0.001) and 1.0 (95% CI -0.2 to -0.18, P = 0.013), respectively. At a median follow-up of 31.4 months, median OS was 13.3 months (95% CI 10.5-18.7) with a significantly longer survival of 18.4 months (95% CI 13.8-23.8) in patients achieving a PSA decline ≥ 50%. At progression following prior response, further LuPSMA was administered to 15 (30%) patients (median 2 cycles commencing 359 days from enrolment) with PSA decline ≥ 50% in 11 patients (73%). 4 of 21 patients (19%) receiving other systemic therapies upon progression experienced PSA decline ≥ 50%. There were no unexpected adverse events with LuPSMA re-treatment. Conclusion: This expanded 50 patient cohort of men with extensive prior therapy confirms our earlier report of high response rates, low toxicity and improved QoL with LuPSMA radioligand therapy. Upon progression, re-challenge LuPSMA demonstrated higher response rates than other systemic therapies.

Purpose: To explore the value of ⁶⁸Ga-PSMA-PET/CT for detection of phosphatase and tensin homolog (PTEN) - loss prostate cancer (PCa). Methods: We retrospectively enrolled 75 patients who underwent multiparametric MRI (mpMRI) and ⁶⁸Ga-PSMA PET/CT before radical prostatectomy. Lesions were outlined on pathological images and regions of interest were drawn on matched mpMRI and PET/CT images. Imaging parameters including average apparent diffusion coefficient (ADCmean) and maximum standardized uptake value (SUV_max) were derived. Immunohistochemical staining was carried out to evaluate the PTEN status. The diagnostic performance of imaging parameters was analyzed by receiver operating characteristics (ROC) analysis. A univariate logistic regression analyses were used to evaluate the association between clinical and imaging variables and PTEN status. Results: Totally, 103 lesions from 54 patients were analyzed. Of these lesions, 34 of 103 (33.0%) showed PTEN-loss status. Our study showed a strong association between SUV_max and PTEN-loss tumors both in the per-patient analysis (P < 0.01) and per-lesion analysis (P < 0.01), yielding the sensitivity and specificity of 0.80 and 0.77 in the per-patient analysis and 0.83 and 0.74 in the per-lesion analysis. Meanwhile, higher pathological PSMA expression was found in the PTEN-deficiency tumors. However, there was no significant difference between PTEN-loss tumors and PTEN-intact tumors using parameters including ADCmean (P > 0.05) and PI-RADS score (P > 0.05). Surprisingly, SUV_max was a significant predictor for detection of PTEN-loss tumors (odds ratio: 7.56, 95% confidence interval: 2.18-26.24, per-patient analysis; odds ratio: 13.66, 95% confidence interval: 4.32-43.24, per-lesion analysis). Conclusion: ⁶⁸Ga-PSMA-PET/CT could effectively detect aggressive PTEN-loss tumors.

Purpose: The aim of this retrospective multicentric study was to develop and evaluate a prognostic FDG PET/CT radiomics signature in early-stage non-small cell lung cancer (NSCLC) patients treated with stereotactic radiotherapy (SBRT). Material and Methods: Patients from 3 different centers (n = 27, 29 and 8) were pooled to constitute the training set, whereas the patients from a fourth center (n = 23) were used as the testing set. The primary endpoint was local control (LC). The primary tumour was semi-automatically delineated in the PET images using the Fuzzy locally adaptive Bayesian algorithm, and manually in the low-dose CT images. A total of 184 IBSI-compliant radiomic features were extracted. Seven clinical and treatment parameters were included. We used ComBat to harmonize radiomic features extracted from the four institutions relying on different PET/CT scanners. In the training set, variables found significant in the univariate analysis were fed into a multivariate regression model and models were built by combining independent prognostic factors. Results: Median follow-up was 21.1 (1.7 – 63.4) and 25.5 (7.7 – 57.8) months in training and testing sets respectively. In univariate analysis, none of the clinical variables, 2 PET and 2 CT features were significantly predictive of LC. The best predictive models in the training set were obtained by combining one feature from PET, namely information correlation 2 (IC2) and one from CT (Flatness), reaching a sensitivity of 100% and a specificity of 96%. Another model combining 2 PET features (IC2 and Strength), reached sensitivity of 100% and specificity of 88%, both with an undefined hazard ratio (HR) (p<0.001). The latter model obtained an accuracy of 0.91 (sensitivity 100%, specificity 81%), with a HR undefined (P = 0.023) in the testing set, however other models relying on CT radiomics features only or the combination of PET and CT features failed to validate in the testing set. Conclusion: We showed that two radiomic features derived from FDG PET were independently associated with LC in patients with NSCLC undergoing SBRT and could be combined in an accurate predictive model. This model could provide local relapse-related information and could be helpful in clinical decision-making.

Purpose: Although the incidence of de novo neuroendocrine prostate cancer (NEPC) is rare, recent data suggests that low expression of prostate-specific membrane antigen (PSMA) is associated with a spectrum of neuroendocrine (NE) hallmarks and androgen receptor (AR)-suppression in prostate cancer (PC). Previous clinical reports indicate that PCs with a phenotype similar to NE tumors can be more amenable to imaging by ¹⁸F-Fluorodeoxyglucose (FDG) rather than PSMA-targeting radioligands. In this study, we evaluated the association between NE gene signature and FDG uptake-associated genes including glucose transporters (GLUTs) and hexokinases, with the goal of providing a genomic signature to explain the reported FDG-avidity of PSMA-suppressed tumors. Methods: Data mining approaches, cell lines and patient-derived xenograft (PDX) models were used to study the levels of 14 members of the SLC2A family (encoding GLUT proteins), 4 members of the hexokinase family (genes: HK1 to 3 and GCK) and PSMA (FOLH1 gene) following AR-inhibition and in correlation with NE hallmarks. Also, we characterize a NE-like PC (NELPC) subset among a cohort of primary and metastatic PC samples with no NE histopathology. We measured glucose uptake in a NE-induced in vitro model and a zebrafish model by non-radioactive imaging of glucose uptake using fluorescent glucose bioprobe, GB2-Cy3. Results: This work demonstrates that a NE gene signature associates with differential expression of genes encoding GLUT and hexokinase proteins. In NELPC, elevated expression of GCK (encoding glucokinase protein) and decreased expression of SLC2A12 correlated with earlier biochemical recurrence. In tumors treated with AR-inhibitors, high expression of GCK and low expression of SLC2A12 correlated with NE histopathology and PSMA gene suppression. GLUT12-suppression and amplification of glucokinase was observed in NE-induced PC cell lines and PDX models. A higher glucose uptake was confirmed in low-PSMA tumors using a GB2-Cy3 probe in a zebrafish model. Conclusion: NE gene signature in NEPC and NELPC associates with a distinct transcriptional profile of GLUTs and HKs. PSMA-suppression correlates with GLUT12-suppression and glucokinase-amplification. Alteration of FDG uptake-associated genes correlated positively with higher glucose uptake in AR and PSMA-suppressed tumors. Zebrafish xenograft tumor models are an accurate and efficient pre-clinical method for monitoring non-radioactive glucose uptake.

Due to their peculiar mechanism of action, the evaluation of radiological response to immune checkpoint inhibitors (ICI) presents many challenges in solid tumors. We aimed to compare the evaluation of first response to Nivolumab by means of CT-based criteria with respect to fluorodeoxyglucose positron emission tomography (FDG-PET) response criteria in non-small-cell lung cancer (NSCLC) patients. Methods: 72 patients with advanced NSCLC were recruited in a mono-institutional ancillary trial within the expanded access program (EAP; NCT02475382) for Nivolumab. Patients underwent CT scan and FDG-PET at baseline and after 4 cycles (first evaluation). In case of progressive disease (PD), an additional evaluation was performed after two further cycles in order to confirm progression. We evaluated the response to treatment with CT scan by means of response evaluation criteria in solid tumors (RECIST) 1.1 and Immuno-related Response Criteria (IrRC) and with FDG-PET by means of PERCIST and immunotherapy-modified-PERCIST (imPERCIST) criteria. The concordance between CT- and PET-based criteria and the capability of each method to predict overall survival (OS) were evaluated. Results: 48/72 patients were evaluable for first response assessment with both PET- and CT-based criteria. We observed low concordance between CT- and PET-based criteria (Kappa value of 0.346 and 0.355 and Kappa value of 0.128 and 0.198 between PERCIST and imPERCIST versus RECIST and irRC respectively). Looking at OS, IrRC were more reliable to distinguish responders from non-responders. However thanks to the prognostic value of partial metabolic response assessed by both PERCIST and Immuno-PERCIST, PET-based response maintained prognostic significant in patients classified as progressive disease on the basis of irRC. Conclusion: Even though the present study did not support the routine use of FDG-PET in the general population of NSCLC patients treated with ICI, it suggests the added prognostic value of the metabolic response assessment, potentially improving the therapeutic decision-making.

Objectives: The detection of cancer micrometastasis for early diagnosis and treatment poses a great challenge for conventional imaging techniques. The aim of study is to evaluate the performance of photoacoustic imaging (PAI) in detecting hepatic micrometastases from melanoma in a very early stage and perform tumor resection by intraoperative photoacoustic image-guidance. Methods: In vivo studies were performed by following protocols approved by the Ethical Committee for Animal Research at Xiamen University. First, a B16 melanoma hepatic metastasis mouse model (n = 10) was established to study the development of micrometastases in vivo. Next, the hepatic metastasis mice models were imaged by scalable PAI instrument, ultrasound, 9.4 T high-resolution magnetic resonance imaging (MRI), positron emission tomography/computed tomography (PET/CT), and bioluminescence imaging. Photoacoustic images acquired with optical wavelengths spanning from 680 to 850 nm were spectrally unmixed by using a linear least-squares method to differentiate various components. Differences in the signal-to-background ratios among different modalities were determined with the two-tailed paired t test. The diagnosis results were assessed with histologic examinations. Excised liver samples from patients diagnosed with hepatic cancer were also examined to identify tumor boundary. In vivo metastatic melanoma removal in surgery was precisely guided by the portable PAI system. Results: PAI achieved as small as ~400 µm hepatic melanoma detection at a depth up to 7 mm in vivo, which could early detect small melanoma compared with ultrasound and MRI in mouse models. The signal ratio of tumor-to-liver acquired with PAI in micrometastases at 8 days (4.2 ± 0.2, n = 6) and 14 days (9.2 ± 0.4, n = 5) were significantly higher than those obtained with PET/CT (1.8 ± 0.1, n = 5 and 4.5 ± 0.2, n = 5, P <0.001 for both). Functional PAI provided dynamic oxygen saturation changes during tumor growth. The limit of detection was measured to be approximately 219 cells per microliter in vitro. We successfully performed intraoperative photoacoustic image-guided surgery in vivo using the rapid portable PAI system. Conclusion: Our findings offer a rapid and effective tool to noninvasively detect micrometastases and guide intraoperative resection as a complementary clinical imaging application.

Calculation of radiation dosimetry in targeted nuclear medicine therapies is traditionally resource-intensive requiring multiple post-therapy SPECT acquisitions. An alternative approach is to take advantage of existing pharmacokinetic data from these smaller cohorts to enable dose computation from a single post-treatment scan in a manner that may be applied to a much broader patient population. Methods: In this work, a technical description for simplified dose estimation is presented and applied to assessment of ¹⁷⁷Lu-PSMA-617 therapy (Prostate-Specific Membrane Antigen) for metastatic prostate cancer. By normalizing existing time-activity curves to a single measurement time, it is possible to calculate a mean and range of time-integrated activity values which relate to radiation absorbed dose. To assist with accurate pharmacokinetic modelling of the training cohort, a method for contour-guided image registration was developed. Results: Tissue-specific dose conversion factors for common post-treatment imaging times are reported along with a characterization of added uncertainty in comparison to a traditional serial imaging protocol. Single time point dose factors for tumor were determined to be 11.0, 12.1, 13.6, and 15.2 Gy per MBq/mL at image times of 24, 48, 72, and 96 hours, respectively. For normal tissues, parotid gland factors were 6.7, 9.4, 13.3, and 19.3 Gy per MBq/mL and kidneys were 7.1, 10.3, 15.0, and 22.0 Gy per MBq/mL at those times. Tumor dose estimates were most accurate using delayed scanning at times beyond 72 hours. Dose to healthy tissues is best characterized by scanning patients in the first two days of treatment owing to the larger degree of tracer clearance in this early phase. Conclusion: The work demonstrates a means for efficient dose estimation in ¹⁷⁷Lu-PSMA-617 therapy. By providing methods to simplify and potentially automate radiation dosimetry we hope to accelerate the understanding of radiobiology and development of dose-response models in this unique therapeutic context.

Purpose: To investigate differences between positron emission tomography/magnetic resonance imaging (PET/MRI) and PET/computed tomography (PET/CT) in lesion detection and classification in oncological whole-body examinations and to investigate radiation exposure differences between both modalities. Material and Methods: In this prospective, single-center, observational study 1003 oncological examinations (918 patients, mean age 57.8±14.4y) were included. Patients underwent PET/CT and subsequent PET/MRI (149.8±49.7min after tracer administration). Examinations were reviewed by radiologists and nuclear medicine physicians in consensus. Additional findings, characterization of indetermiante findings in PETCT, missed findings in PET/MRI including their clinical relevance and effective dose of both modalities were investigated. McNemar’s test was used to compare lesion detection between both hybrid imaging modalities (p<0.001 indicating statistical significance). Results: Additional information in PET/MRI was reported in 26.3% (264/1003) of examinations compared to PET/CT (p<0.001). Of these, additional malignant findings were detected in 5.3% (53/1003), leading to a change in TNM-staging in 2.9% (29/1003) due to PET/MRI. Definite lesion classification of indeterminate PET/CT findings was possible in 11.1% (111/1003) with PET/MRI. In 2.9% (29/1003), lesions detected in PET/CT were not visible in PET/MRI. Malignant lesions were missed in 1.2% (12/1003) by PET/MRI leading to a change in TNM-staging in 0.5% (5/1003). The estimated mean effective-dose for whole-body PET/CT amounted to 17.6±8.7mSv in comparison to 3.6±1.4mSv in PET/MRI, resulting in a potential dose reduction of 79.6% (p<0.001). Conclusion: PET/MRI improves lesion detection and potentially reduces additional examinations in tumor staging. Especially younger patients may benefit from the clinically relevant dose reduction of PET/MRI compared to PET/CT.

Introduction: The aim of this study was to analyze patterns of persistent versus recurrent or new PET lesions in a selected patient cohort with PSA persistence following salvage lymph node dissection (SLND) and pre/post procedure prostate-specific membrane antigen ligand positron emission tomography (PSMA-PET). Material and Methods: 16 patients were included in this multicenter study. Inclusion criteria were: a) PSMA-PET performed for biochemical recurrence before SLND (pre-SLND PET) and b) repeat PSMA-PET performed for persistently elevated PSA level (≥0.1 ng/mL) ≥6 weeks after SLND (post-SLND PET). Image analysis was performed by three independent nuclear medicine physicians applying the molecular imaging TNM system PROMISE. Lesions were confirmed by histopathology, presence on correlative CT/MRI/bone scan or PSA response after focal therapy. Results: post-SLND PET identified PCa-lesions in 88% (14/16) of patients with PSA persistence after SLND. Median PSA was 1.2 ng/mL (IQR, 0.6-2.8 ng/mL). Disease was confined to the pelvis in 56% of patients (9/16) and most of these men had common iliac (6/16, 38%) and internal iliac lymph node metastases (6/16, 38%). Extrapelvic disease was detected in 31% of patients (5/16). In pre- and post-SLND PET comparison, 10/16 had at least one lesion already detected at baseline (63% PET persistence); 4/16 had new lesions only (25% PET recurrence); 2 had no disease on post-SLND PET. All validated regions (11 regions in 9 patients) were true positive. 9/14 (64%) patients underwent repeat local therapies after SLND (7/14 radiotherapy, 2/14 surgery). Conclusion: SLND of pelvic nodal metastases was often not complete according to PSMA-PET. About two thirds of patients had PET positive nodal disease after SLND already seen on pre-SLND PSMA-PET. Notably, about one quarter of patients had new lesions, not detected by pre-surgical PSMA-PET.

Acute myocardial infarction (MI) triggers a local and systemic inflammatory response. We recently showed microglia involvement using TSPO imaging. Here, we evaluate whether ¹¹C-methionine provides further insights into heart-brain inflammation networking. Methods: Male Bl6N mice underwent permanent coronary artery ligation followed by ¹¹C-methionine PET at 3 and 7 days (n = 3). In subgroups, leukocyte homing was blocked by integrin antibodies (n = 5). The cellular substrate for PET signal was identified using brain section immunostaining. Results: ¹¹C-methionine uptake peaked in the MI region at d3 (5.9±0.9vs 2.4±0.5 %ID/cc), decreasing to control level by d7 (4.3±0.6 %ID/cc). Brain uptake was proportional to cardiac uptake (r=0.47,p<0.05), peaking also at d3 (2.9±0.4vs 2.4±0.3 %ID/cc) and returning to baseline at d7 (2.3±0.4 %ID/cc). Integrin blockade reduced uptake at every time point. Immunostaining at d3 revealed co-localization of the L-type amino acid transporter with GFAP-positive astrocytes but not CD68-positive microglia. Conclusion: PET imaging with ¹¹C-methionine specifically identifies an astrocyte component, enabling further dissection of the heart-brain axis in post MI inflammation.

We performed post-hoc analyses on the utility of pre-therapeutic and early interim ⁶⁸Ga-DOTA-Tyr3-octreotide (⁶⁸Ga-DOTATOC) positron emission tomography (PET) tumor uptake and volumetric parameters and a recently proposed biomarker, the inflammation-based index (IBI), for peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumor (NET) patients treated with ⁹⁰Y-DOTATOC in the setting of a prospective phase II trial. Methods: Forty-three NET patients received up to four cycles of 1.85 GBq/m²/cycle ⁹⁰Y-DOTATOC with a maximal kidney biologic effective dose of 37 Gy. All patients underwent a ⁶⁸Ga-DOTATOC PET/computed tomography (CT) at baseline and seven weeks after the first PRRT cycle. ⁶⁸Ga-DOTATOC-avid tumor lesions were semi-automatically delineated using a customized standardized uptake value (SUV) threshold-based approach. PRRT response was assessed on CT using RECIST 1.1. Results: Median progression-free survival (PFS) and overall survival (OS) were 13.9 and 22.3 months, respectively. An SUVmean higher than 13.7 (75th percentile (P75)) was associated with better survival (hazard ratio (HR) 0.45; P = 0.024), whereas a ⁶⁸Ga-DOTATOC-avid tumor volume higher than 578 ml (P75) was associated with worse OS (HR 2.18; P = 0.037). Elevated baseline IBI was associated with worse OS (HR 3.90; P = 0.001). Multivariate analysis corroborated independent associations between OS and SUVmean (P = 0.016) and IBI (P = 0.015). No significant correlations with PFS were found. A composite score based on SUVmean and IBI allowed to further stratify patients in three categories with significantly different survival. On early interim PET, a decrease in SUVmean of more than 17% (P75) was associated with worse survival (HR 2.29; P = 0.024). Conclusion: Normal baseline IBI and high ⁶⁸Ga-DOTATOC tumor uptake predict better outcome in NET patients treated with ⁹⁰Y-DOTATOC. This can be used for treatment personalization. Interim ⁶⁸Ga-DOTATOC PET does not provide information for treatment personalization.

The PET radiotracer ⁶⁸Ga-PSMA-HBED-CC (⁶⁸Ga-PSMA-11) shows potential as an imaging biomarker for recurrent and metastatic prostate cancer. The purpose of this study was to determine repeatability of ⁶⁸Ga-PSMA-HBED-CC in a test-retest trial in subjects with metastatic prostate adenocarcinoma. Methods: Subjects with metastatic prostate cancer underwent two PET/CT scans with ⁶⁸Ga-PSMA-HBED-CC within 14 days (mean 6 ± 4 d). Lesions in bone, nodes, prostate/bed, and visceral organs as well as representative normal tissues (salivary glands and spleen) were segmented separately by two readers. Absolute and percent differences in SUV_max and SUVmean were calculated for all test-retest regions. Repeatability was assessed using percentage difference, within-subject coefficient of variation (wCV), repeatability coefficient (RC), and Bland-Altman analysis. Results: 18 subjects were evaluated, 16 of which demonstrated local or metastatic disease on ⁶⁸Ga-PSMA-HBED-CC PET/CT. A total of 136 lesions were segmented in bone (n = 99), nodes (n = 27), prostate/bed (n = 7), and viscera (n = 3). The wCV for SUV_max was 11.7% for bone lesions and 13.7% for nodes. The RC was ±32.5% SUV_max for bone lesions and ±37.9% SUV_max for nodal lesions, meaning 95% of the normal variability between two measurements will be within these numbers, so larger differences are likely attributable to true biological changes in tumor rather than normal physiologic or measurement variability. wCV in the salivary glands and spleen was 8.9% and 10.7% SUVmean, respectively. Conclusion: Repeatability measurements for PET/CT test-retest with ⁶⁸Ga-PSMA-HBED-CC show a wCV 12-14% SUV_max and RC ±33-38% SUV_max in bone and nodal lesions. These estimates are an important aspect of ⁶⁸Ga-PSMA-HBED-CC as a quantitative imaging biomarker. These estimates are similar to those reported for ¹⁸F-FDG, suggesting that ⁶⁸Ga-PSMA-HBED-CC PET/CT may be useful in monitoring response to therapy.

P-glycoprotein (ABCB1) plays an important role at the blood-brain barrier (BBB) in promoting the clearance of neurotoxic beta-amyloid (Aß) peptides from the brain into the blood. ABCB1 expression and activity were found to be decreased in the brains of Alzheimer disease (AD) patients. Treatment with drugs which induce cerebral ABCB1 activity may be a promising approach to delay the build-up of Aß deposits in the brain by enhancing the clearance of Aß peptides from the brain. The aim of this study was to investigate whether PET with the weak ABCB1 substrate radiotracer ¹¹C-metoclopramide can measure ABCB1 induction at the BBB in a beta-amyloidosis mouse model (APP/PS1-21 mice) and in wild-type mice. Methods: Groups of wild-type and APP/PS1-21 mice aged 50 or 170 days underwent ¹¹C-metoclopramide baseline PET scans or scans after intraperitoneal treatment with the rodent pregnane X receptor (PXR) activator 5-pregnen-3β-ol-20-one-16α-carbonitrile (PCN, 25 mg/kg) or its vehicle over 7 days. At the end of the PET scans, brains were harvested for immunohistochemical analysis of ABCB1 and Aß levels. In separate groups of mice, radiolabeled metabolites of ¹¹C-metoclopramide were determined in plasma and brain at 15 min after radiotracer injection. As an outcome parameter of cerebral ABCB1 activity, the elimination slope of radioactivity washout from the brain (kE,brain) was calculated. Results: PCN treatment resulted in an increased clearance of radioactivity from the brain as reflected by significant increases in kE,brain (from +26% to +54% relative to baseline). Immunohistochemical analysis confirmed ABCB1 induction in the brains of PCN-treated APP/PS1-21 mice with a concomitant decrease in Aß levels. There was a significant positive correlation between kE,brain values and ABCB1 levels in the brain. In wild-type mice, a significant age-related decrease in kE,brain values was found. Metabolite analysis showed that the majority of radioactivity in the brain was composed of unmetabolized ¹¹C-metoclopramide in all animal groups. Conclusion: ¹¹C-metoclopramide can measure ABCB1 induction in the mouse brain without the need to consider an arterial input function and may find potential application in AD patients to non-invasively evaluate strategies to enhance the clearance properties of the BBB.

Background: Accurate definition of the extent and severity of left-ventricular assist device (LVAD) infection may facilitate therapeutic decision making and targeted surgical intervention. Here, we explore the value of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) for guidance of patient management. Methods: Fifty-seven LVAD-carrying patients received 85 whole-body ¹⁸F-FDG PET/CT scans for the work-up of device infection. Clinical follow-up was obtained over a period of up to two years. Results: PET/CT showed various patterns of infectious involvement of the 4 LVAD components: driveline entry point (77% of cases), subcutaneous driveline path (87%), pump pocket (49%) and outflow tract (58%). Driveline smears revealed staphylococcus or pseudomonas strains as the underlying pathogen in a majority of cases (48 and 34%, respectively). At receiver-operating characteristics analysis, an ¹⁸F-FDG standardized uptake value (SUV) >2.5 was most accurate to identify smear-positive driveline infection. Infection of 3 or all 4 LVAD components showed a trend towards lower survival vs infection of 2 or less components (P = 0.089), while involvement of thoracic lymph nodes was significantly associated with adverse outcome (P = 0.001 for nodal SUV above vs below median). Finally, patients that underwent early surgical revision within 3 months after PET/CT (n = 21) required significantly less inpatient hospital care during follow-up when compared to those receiving delayed surgical revision (n = 11; p<0.05). Conclusion: Whole-body ¹⁸F-FDG PET/CT identifies the extent of LVAD infection and predicts adverse outcome. Initial experience suggests that early image-guided surgical intervention may facilitate a less complicated subsequent course.

Cri-Du-Chat Syndrome (CdCs) is a rare genetic disease caused by a deletion in the short arm of chromosome 5 (5p) with a variable clinical spectrum. To date no study in literature has ever investigated the alterations of brain glucose metabolism in these subjects by means of [¹⁸F]fluoro-2-deoxy-d-glucose Positron Emission Tomography/Computed Tomography (¹⁸F-FDG PET/CT). The aims of this study were to detect difference in brain FDG metabolism in patients affected by CdCs with different clinical presentations and identify possible "brain metabolic phenotypes" of this syndrome. Methods: 6 patients (age: 5 M and 1 F, age range: 10-27) with CdCs were assessed for presence of cognitive and behavioral symptoms with a battery of neuropsychological tests and then classified as patient with a severe or mild phenotype. Then, patients underwent a brain ¹⁸F-FDG PET/CT scan. PET/CT findings were compared to a control group, matched for age and sex, by using statistical parametric mapping (SPM). Association of different clinical phenotypes and ¹⁸F-FDG PET/CT findings was investigated. Results: Four patients presented a severe phenotype, whereas 2 patients demonstrated mild phenotype. SPM single subject and group analysis compared to the control cohort revealed a significant hypometabolism in the left temporal lobe (BAs 20, 36 and 38), in the right frontal subcallosal gyrus (BA 34) and caudate body, and in the cerebellar tonsils (p<0.001). Hypermetabolism (P = 0.001) was revealed in the right superior and precentral frontal gyrus (BA 6) in patient group compared to the control cohort. In SPM single subject analysis the hypermetabolic areas were detected only in patients with a severe phenotype. Conclusion: This study revealed different patterns of brain glucose metabolism in patients with severe and mild phenotype compared to control subjects. In particular, the hypermetabolic abnormalities in the brain, evaluated by¹⁸F-FDG PET/CT, seem to correlate with the severe phenotype in patients with CdCs.

Background: Targeting cancer-associated fibroblasts (CAFs) has become an attractive goal for diagnostic imaging and therapy as they can constitute as much as 90% of tumor mass. The serine protease fibroblast activation protein (FAP) is overexpressed selectively in CAFs, drawing interest in FAP as a stromal target. The quinoline-based FAP-inhibitor PET tracer, ⁶⁸Ga-FAPI-04, has been previously shown to yield high tumor-to-background ratios (TBR) in patients with various cancers. Recent developments towards an improved compound for therapeutic application have identified FAPI-46 as a promising agent due to a longer tumor retention time in comparison with FAPI-04. Here we present a PET biodistribution and radiation dosimetry study of ⁶⁸Ga-FAPI-46 in cancer patients. Methods: Six patients with different cancers underwent serial ⁶⁸Ga-FAPI-46 PET/CT scans at three time points following radiotracer injection: 10 minutes, 1 hour, and 3 hours. The source organs consisted of the kidneys, bladder, liver, heart, spleen, bone marrow, uterus, and body remainder. OLINDA/EXM v.1.1 software was used to fit and integrate the kinetic organ activity data to yield total body and organ time-integrated activity coefficients/residence times and finally organ absorbed doses. Standardized uptake values (SUV) and TBR were generated from the contoured tumor and source organ volumes. Spherical volumes in muscle and blood pool were also obtained for TBR (Tumor SUV_max / Organ SUVmean). Results: At all timepoints, the highest organ SUV_max was observed in the liver. Tumor and organ mean SUVs decreased whereas TBRs in all organs but the uterus increased with time. The highest TBRs at 3 hours were observed with the bone marrow (31.1), muscle (22.8), heart (19.1), and spleen (19.0). Organs with the highest effective doses were the bladder wall (2.41E-03 mSv/MBq), followed by ovaries (1.15E-03 mSv/MBq) and red marrow (8.49E-04mSv/MBq). The average effective total body dose was 7.80E-03 mSv/MBq. Thus for administration of 200 MBq ⁶⁸Ga-FAPI-46 the effective total body dose is 1.56 mSv ± 0.26 mSv, in addition to approximately 3.7 mSv from one low-dose CT scan done for attenuation correction. Conclusion: ⁶⁸Ga-FAPI-46 PET/CT has a favorable dosimetry profile with an estimated whole body dose of 5.3 mSv for an administration of 200 MBq (5.4 mCi) of ⁶⁸Ga-FAPI-46 (1.56± 0.26 mSv from the PET tracer and 3.7 mSv from one low-dose CT scan). The biodistribution study showed high TBRs increasing over time, suggesting high diagnostic performance and favorable tracer kinetics for potential therapeutic applications.

2-Deoxy-2-[18F]fluoro-D-glucose (2-FDG) with positron emission tomography (2-FDG-PET) is undeniably useful in the clinic, among other uses, to monitor change over time using the 2-FDG standardized uptake values (SUV) metric. This report suggests some potentially serious caveats for this and related roles for 2-FDG PET. Most critical is the assumption that there is an exact proportionality between glucose metabolism and 2-FDG metabolism, called the lumped constant, LC. This report describes that LC is not constant for a specific tissue and may be variable before and after disease treatment. The purpose of this work is not to deny the clinical value of 2-FDG PET; it is a reminder that when one extends the use of an appropriately qualified imaging method, new observations may arise and further validation would be necessary. Current understanding of glucose-based energetics in vivo is based on the quantification of glucose metabolic rates with 2-FDG PET, a method that permits the non-invasive assessment in various human disorders. However, 2-FDG is only a good substrate for facilitated-glucose transporters (GLUTs) but not for sodium-dependent glucose co-transporters (SGLTs), which have recently been shown to be distributed in multiple human tissues. Thus, the GLUT-mediated in vivo glucose utilization measured by 2-FDG PET would be blinded to the potentially substantial role of functional SGLTs in glucose transport and utilization. Therefore, in these circumstances the 2-FDG LC used to quantify in vivo glucose utilization should not be expected to remain constant. 2-FDG LC variations have been especially significant in tumors, particularly at different stages of cancer development, affecting the accuracy of quantitative glucose measures and potentially limiting the prognostic value of 2-FDG, as well as its accuracy in monitoring treatments. SGLT-mediated glucose transport can be estimated using α-methyl-4-deoxy-4-[18F]fluoro-D-glucopyranoside (Me-4FDG). Utilizing both 2-FDG and Me-4FDG should provide a more complete picture of glucose utilization via both GLUT and SGLT transporters in health and disease stages. Given the widespread use of 2-FDG PET to infer glucose metabolism, appreciating the potential limitations of 2-FDG as a surrogate for glucose metabolic rate and the potential reasons for variability in LC is relevant. Even when the readout for the 2-FDG PET study is only an SUV parameter, variability in LC is important, particularly if it changes over the course of disease progression (e.g., an evolving tumor).

Due to improvements in quantitative SPECT/CT, voxel-based dosimetry for radionuclide therapies has aroused growing interest as it promises the visualization of absorbed doses at a voxel level. In this work, SPECT/CT-based voxel-based dosimetry of a 3D printed 2-compartment kidney phantom was performed, and the resulting absorbed dose distributions were examined. Additionally, the potential of the PETPVC partial-volume correction tool was investigated. Methods: Both kidney compartments (70% cortex, 30% medulla) were filled with different activity concentrations and SPECT/CT imaging was performed. The images were reconstructed using varying reconstruction settings (iterations, subsets, and post-filtering). Based on these activity concentration maps, absorbed dose distributions were calculated with pre-calculated ¹⁷⁷Lu voxel S values and an empirical kidney half-life. An additional set of absorbed doses was calculated after applying PETPVC for partial-volume correction of the SPECT reconstructions. Results: SPECT/CT imaging blurs the two discrete sub-organ absorbed dose values into a continuous distribution. While this effect is slightly improved by applying more iterations, it is enhanced by additional post-filtering. By applying PETPVC, the absorbed dose values are separated into 2 peaks. Although this leads to a better agreement between SPECT/CT-based and nominal values, considerable discrepancies remain. In contrast to the calculated nominal absorbed doses of 7.8/1.6 Gy (cortex/medulla), SPECT/CT-based voxel-level dosimetry resulted in mean absorbed doses ranging from 3.0-6.6 Gy (cortex) and 2.7-5.1 Gy (medulla). PETPVC led to improved ranges of 6.1-8.9 Gy (cortex) and 2.1-5.4 Gy (medulla). Conclusion: Our study shows that ¹⁷⁷Lu quantitative SPECT/CT imaging leads to voxel-based dose distributions largely differing from the real organ distribution. SPECT/CT imaging and reconstruction deficiencies might directly translate into unrealistic absorbed dose distributions, thus questioning the reliability of SPECT-based voxel-level dosimetry. Therefore, SPECT/CT reconstructions should be adapted to ensure an accurate quantification of the underlying activity and, therefore, absorbed dose in a volume-of-interest of the expected object size (e.g. organs, organ sub-structures, lesions or voxels). As an example, PETPVC largely improves the match between SPECT/CT-based and nominal dose distributions. In conclusion, the concept of voxel-based dosimetry should be treated with caution. Specifically, it should be kept in mind that the absorbed dose distribution is mainly a convolved version of the underlying SPECT reconstruction.

Purpose: To evaluate ¹¹C-choline PET/CT detection performance for biochemically recurrent prostate cancer (PCa) in a large non-European cohort in the context of emerging evidence for PSMA PET in this setting, and to map patterns of PCa recurrence. Methods: We retrospectively analyzed ¹¹C-choline PET/CT scans from 287 patients who were enrolled onto an imaging protocol based on rising prostate-specific antigen (PSA) levels (mean:3.43 ng/mL, median:0.94 ng/mL, range:0.15–89.91) and suspected recurrent PCa. A total of 187 patients had undergone primary radical prostatectomy (RP; 79/187 had secondary radiotherapy), 30 had undergone primary radiotherapy (RT), and 70 had persistent PSA elevation after receiving initial treatment (69 post-RP, 1 post-RT). The level of suspicion for recurrence on ¹¹C-choline PET/CT was scored (0:negative, 1:equivocal, 2:positive) by two readers. The correlation between ¹¹C-choline PET/CT positivity and initial treatment, Gleason score, NCCN stage, PSA level, PSA doubling time, PSA velocity, and time between initial treatment and PET imaging was evaluated. Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria were used to map ¹¹C-choline recurrence patterns. Results: Considering scores 1 and 2 as positives, consensus between the two readers deemed 66% of the ¹¹C-choline PET/CT scans as positive. When sorted by PSA level, 45% of patients with PSA<0.5 ng/mL, 56% of patients with PSA 0.5–0.99 ng/mL, 70% of patients with PSA 1.0–1.99 ng/mL, and 90% of patients with PSA ≥2.0 ng/mL scored either 1 or 2 on ¹¹C-choline PET/CT scans. When considering scores of 2 only, ¹¹C-choline PET/CT positivity was 54% (28%, 46%, 62%, and 81%, respectively, for patients with PSA <0.5 ng/mL, 0.5–0.99 ng/mL, 1.0–1.99 ng/mL, and ≥2.0 ng/mL). In multivariate analysis, only the PSA level was significantly associated with scan positivity. Pattern analysis showed that pelvic lymph nodes were the most common site of recurrence, and 28% of patients had ¹¹C-choline-positive suspected recurrences outside the initial treatment field. Conclusion: ¹¹C-choline PET/CT can detect PCa recurrence even among patients with low PSA levels when interpretation accounts for the clinical context, providing a certain pre-test probability. Until PSMA agents are fully approved for PCa, choline PET/CT may provide clinical utility.

⁶⁸Ga-DOTATOC-PET/MRI (⁶⁸Gallium-DOTATOC-positron emission tomography/magnetic resonance imaging) combines the advantages of PET in the acquisition of metabolic-functional information with the high soft tissue contrast of MRI. Standardized uptake values (SUV) in tumors were suggested as a measure of somatostatin receptor expression. A challenge with receptor ligands is, that the distribution volume is confined to tissues with tracer-uptake, potentially limiting SUV quantification. In this study, different functional, three-dimensional (3D) SUV, apparent diffusion coefficient (ADC) parameters and arterial tumor enhancement were tested for the characterization of gastroendopancreatic neuroendocrine tumors (GEP-NET). Methods: For this single-center, cross-sectional study, 22 patients with 24 histologically confirmed GEP-NET lesions (15 men/7 women; median, 61 years, range, 43-81 years), who received hybrid ⁶⁸Ga-DOTA-PET/MRI examinations at 3T between January 2017 and July 2019 met eligibility criteria. SUVs, tumor-to-background ratios (TBR), the total functional tumor volume (TFTV), ADCmean and ADCmin were measured based on volumes of interest (VOI) and examined with receiver operating characteristic analysis to determine cut-off values for differentiation between low and intermediate grade GEP-NET. Spearman’s rank correlation coefficients were used to assess correlations between functional imaging parameters. Results: The ratio of PET-derived SUVmean and diffusion-weighted imaging (DWI)-derived ADCmin was introduced as a combined variable to predict tumor grade, outperforming single predictors. Based on a threshold ratio of 0.03 to be exceeded, tumors could be classified as grade 2 with a sensitivity of 86% and specificity of 100%. SUV and functional ADC values as well as arterial contrast enhancement parameters showed non-significant and mostly negligible correlations. Conclusion: As receptor density and tumor cellularity appear to be independent, potentially complementary phenomena, the combined PET/MRI ratio SUVmean/ADCmin may be used as a novel biomarker, allowing to differentiate between grade 1 and 2 GEP-NET.

Rationale: Despite its widespread use in oncology, the PET radiotracer ¹⁸F-FDG is ineffective for improving early detection of pancreatic ductal adenocarcinoma (PDAC). An alternative strategy for early detection of pancreatic cancer involves visualisation of high-grade pancreatic intraepithelial neoplasias (PanIN-3), generally regarded as the non-invasive precursors of PDAC. The DNA damage response is known to be hyper-activated in late-stage PanINs. Therefore, we investigated whether the SPECT imaging agent, ¹¹¹In-anti-H2AX-TAT, allows visualisation of the DNA damage repair marker H2AX in PanIN-3s in an engineered mouse model of PDAC, to facilitate early detection of PDAC. Methods: Genetically engineered KPC mice (KRasLSL.G12D/+; p53LSL.R172H/+; PdxCre) were imaged with ¹⁸F-FDG and ¹¹¹In-anti-H2AX-TAT. PanIN/PDAC presence visualised by histology was compared with autoradiography and immunofluorescence. Separately, the survival of KPC mice imaged with ¹¹¹In-anti-H2AX-TAT was evaluated. Results: In KPC mouse pancreata, H2AX expression was increased in high-grade PanINs, but not in PDAC, corroborating earlier results obtained from human pancreas sections. Uptake of ¹¹¹In-anti-H2AX-TAT, but not ¹¹¹In-IgG-TAT or ¹⁸F-FDG, within the pancreas was positively correlated with the age of KPC mice, which was correlated with the number of high-grade PanINs. ¹¹¹In-anti-H2AX-TAT localises preferentially in high-grade PanIN lesions, but not in established PDAC. Younger, non-tumour-bearing KPC mice that show uptake of ¹¹¹In-anti-H2AX-TAT in the pancreas survive significantly shorter than mice with physiological ¹¹¹In-anti-H2AX-TAT uptake. Conclusion: ¹¹¹In-anti-H2AX-TAT imaging allows non-invasive detection of DNA damage repair signalling upregulation in pre-invasive PanIN lesions and is a promising new tool to aid in the early detection and staging of pancreatic cancer.

Prediction of post-operative pulmonary function in lung cancer patients before tumor resection is essential for patient selection for surgery and is conventionally done with a non-imaging segment counting method (SC) or a two-dimensional planar lung perfusion scintigraphy (PS). The purpose of this study was to compare quantitative analysis of PS to single photon emission computed tomography/computed tomography (SPECT/CT) and to estimate the accuracy of SC, PS and SPECT/CT in predicting post-operative pulmonary function in patients undergoing lobectomy. Methods: Seventy-five non-small cell lung cancer (NSCLC) patients planned for lobectomy were prospectively enrolled (68% males, average age 68.1±8 years ). All patients completed pre-operative forced expiratory volume capacity (FEV1), diffusing capacity of the lung for carbon monoxide (DLCO), Tc99m-MAA lung perfusion scintigraphy with PS and SPECT/CT quantification. A subgroup of 60 patients underwent video-assisted thoracoscopic (VATS) lobectomy and measurement of post-operative FEV1 and DLCO. Relative uptake of the lung lobes estimated by PS and SPECT/CT were compared. Predicted post-operative FEV1 and DLCO were derived from SC, PS and SPECT/CT. Prediction results were compared between the different methods and the true post-operative measurements in patients who underwent lobectomy. Results: Relative uptake measurements differed significantly between PS and SPECT/CT in right lung lobes, with a mean difference of -8.2±3.8, 18.0±5.0 and -11.5±6.1 for right upper, middle and lower lobes respectively (p<0.001). The differences between the methods in the left lung lobes were minor with a mean difference of -0.4±4.4 (p>0.05) and -2.0±4.0 (p<0.001) for left upper and lower lobes respectively. No significant difference and strong correlation (R=0.6-0.76, p<0.001) were found between predicted post-operative lung function values according to SC, PS, SPECT/CT and the actual post-operative FEV1 and DLCO. Conclusion: Although lobar quantification parameters differed significantly between PS and SPECT/CT, no significant differences were found between the predicted post-operative lung function results derived from these methods and the actual post-operative results. The additional time and effort of SPECT/CT quantification may not have an added value in patient selection for surgery. SPECT/CT may be advantageous in patients planned for right lobectomies but further research is warranted.

Triple negative breast cancer (TNBC) remains the most aggressive subtype of breast cancer leading to the worst prognosis. Because current therapeutic approaches lack efficacy, there is a clinically unmet need for effective treatment alternatives. Herein, we demonstrate a promising strategy utilizing a tumor-targeting alkylphosphocholine (NM600) radiolabeled with ¹⁷⁷Lu for targeted radionuclide therapy (TRT) of TNBC. In two murine syngeneic models of TNBC, we confirmed excellent tumor targeting and rapid normal tissue clearance of the PET imaging analog ⁸⁶Y-NM600. Based on longitudinal PET/CT data acquired with ⁸⁶Y-NM600, we estimated the dosimetry of therapeutic ¹⁷⁷Lu-NM600, which showed larger absorbed doses in the tumor compared to normal tissues. Administration of ¹⁷⁷Lu-NM600 resulted in significant tumor growth inhibition and prolonged overall survival in mice bearing syngeneic 4T07 and 4T1 tumors. Complete response was attained in 60% of 4T07 bearing mice, but animals carrying aggressive 4T1 tumor grafts succumbed to metastatic progression. The injected activities used for treatment (9.25 and 18.5 MBq) were well tolerated, and only mild transient cytopenia was noted. Overall, our results suggest that ¹⁷⁷Lu-NM600 TRT has potential for treatment of TNBC and merits further exploration in a clinical setting.

Introduction: A new pattern of response, so-called hyper-progressive disease (HPD), is emerging during treatment with immune checkpoint inhibitors (ICI). Our aim was to investigate the prevalence of such phenomenon and to assess its association with clinical variables and metabolic parameters by ¹⁸F-fludeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT). Methods: Data from 50 patients (34 male, 16 female, median age 73) with non-small cell lung carcinoma (NSCLC) and treated with ICI were prospectively collected. All patients underwent contrast-enhanced CT, ¹⁸F-FDG PET/CT, and complete peripheral blood sample at baseline before ICI. HPD was defined according to clinical and radiologic criteria. Because of the rapid disease progression or worsening of clinic conditions, radiologic response assessment was available for 46 patients. OS were analyzed using the Kaplan–Meier method and the log-rank test. A Cox proportional hazards regression analysis was used to evaluate factors independently associated with OS. Median follow-up was 12.4 months (9.7-15.2 months). Results: We identified the following response categories: 10 cases as complete/partial response (CR/PR), 17 cases with stable disease (SD), 5 patients with progressive disease (PD), and 14 with HPD. Among metabolic parameters we observed a statistically significant association between HPD status and tumor burden, expressed by both MTV (756.1ml for HPD vs 475.6ml for non-HPD, P = 0.011) and TLG (287.3 for HPD vs 62.1 for non-HPD, P = 0.042). Among clinical variables, 12/14 patients (85.7%) within the HPD group compared with 8/32 patients (25%) in the non-HDP group had more than two metastatic sites (p<0.001). In addition, the derived neutrophil-to-lymphocyte ratio (dNLR) and platelet counts was significantly associated with HPD status (P = 0.038, P = 0.025, respectively). Survival analysis showed a median OS of 4 months for HPD group compared with 15 months within non-HPD patients (P = 0.003). Likewise, median OS was significantly different when we considered all the response categories: CR/PR, SD, PD, and HPD (P = 0.001). Finally, Multivariate analysis identified MTV and dNLR as independent predictors for OS. Conclusion: Our results suggest that the use of ICI might represent a concern in patients with high metabolic tumor burden and inflammatory indexes at baseline. However Additional studies are needed.

Multiple myeloma (MM) is a plasma cell cancer and represents the second most frequent hematological malignancy. Despite new treatments and protocols including high doses chemotherapy associated with autologous stem cell transplantation, the prognosis of MM patients is still poor. Alpha-radioimmunotherapy (alpha-RIT) represents an attractive treatment strategy due to the high linear energy transfer and short path length of alpha-radiation in tissues, resulting in high tumor cell killing and low toxicity to surrounding tissues. In this study, we investigated the potential of alpha-RIT with ²¹²Pb-Daratumumab (anti-CD38), in both in vitro and in vivo models, as well as an anti-mouse CD38 antibody using in vivo models. Methods: Inhibition of cell proliferation after incubation of RPMI8226 cell line with increasing activities (0.185-3.7 kBq/ml) of ²¹²Pb-isotypic control or ²¹²Pb-Daratumumab was evaluated. Biodistribution was performed in vivo by SPECT-CT imaging and post-mortem. Dose range finding (DRF) and acute toxicity studies were conducted. As Daratumumab does not bind the murine CD38, biodistribution and DRF were also determined using an anti-murine CD38 antibody. To evaluate in vivo efficacy of ²¹²Pb-Daratumumab, mice were engrafted subcutaneously with 5.106 RPMI8226 cells. Mice were treated 13 days post-engraftment with an intravenous injection of ²¹²Pb-Daratumumab or control solutions. Therapeutic efficacy was monitored by tumor volume measurements and overall survival. Results: Significant inhibition of proliferation of the human myeloma RPMI8226 cell line was observed after three days of incubation with ²¹²Pb-Daratumumab compared to ²¹²Pb-Isotypic Control or cold antibodies. Biodistribution studies showed a specific tumoral accumulation of Daratumumab. No toxicity was observed with ²¹²Pb-Daratumumab up to 370 kBq due to the lack of cross-reactivity. Nevertheless, acute toxicity experiments with ²¹²Pb-anti-mCD38 established a toxic activity of 277.5 kBq. To remain within realistically safe treatment activities for efficacy studies, mice were treated with 185 kBq or 277.5 kBq of ²¹²Pb-Daratumumab. Marked tumor growth inhibition compared to controls was observed, with a median survival of 55 days for 277.5 kBq of ²¹²Pb-Daratumumab instead of 11 for PBS control groups. Conclusion: These results showed ²¹²Pb-Daratumumab efficacy on xenografted mice with significant tumor regression and increased survival. This study highlights alpha-RIT potency in MM treatment.

Rationale: The presence of metastasis in local lymph nodes (LNs) is a key factor influencing choice of therapy and prognosis in cervical and endometrial cancers; therefore, the exploration of sentinel LNs (SLNs) is highly important. Currently, however, SLN mapping requires LN biopsy for pathologic evaluation, since there are no clinical imaging approaches that can identify tumor-positive LNs in early stages. Staging lymphadenectomy poses risks, such as leg lymphedema or lymphocyst formation. Furthermore, in 80% to 90% of patients, the explored LNs are ultimately tumor free, meaning the vast majority of patients are unnecessarily subjected to lymphadenectomy. Methods: Current lymphoscintigraphy methods only identify the anatomic location of the SLNs but do not provide information on their tumor status. There are no non-invasive methods to reliably identify metastases in LNs before surgery. We have developed positron lymphography (PLG), a method to detect tumor-positive LNs, where ¹⁸F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) is injected interstitially into the uterine cervix the day of surgery, and its rapid transport through the lymphatic vessels to the SLN is then visualized with dynamic positron emission tomography/computed tomography (PET/CT). We previously showed that PLG was able to identify metastatic LNs in animal models. Here, we present the first results from our pilot clinical trial (clinical trials identifier NCT02285192) in 23 patients with uterine or cervical cancer. On the morning of surgery, ¹⁸F-FDG was injected into the cervix, followed by an immediate dynamic PET/CT scan of the pelvis and a delayed 1-h whole body scan. Results: There were 3 (15%) node-positive cases on final pathologic analysis, and all LNs (including one with a focus of only 80 tumor cells) were identified by PLG except one node with an 11-mm micrometastasis. There were 2 (10%) false-positive cases with PLG, in which final pathology of the corresponding SLNs was negative for tumor. Methods: Current lymphoscintigraphy methods only identify the anatomic location of the SLNs but do not provide information on their tumor status. There are no non-invasive methods to reliably identify metastases in LNs before surgery. We have developed positron lymphography (PLG), a method to detect tumor-positive LNs, where ¹⁸F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) is injected interstitially into the uterine cervix the day of surgery, and its rapid transport through the lymphatic vessels to the SLN is then visualized with dynamic positron emission tomography/computed tomography (PET/CT). We previously showed that PLG was able to identify metastatic LNs in animal models. Here, we present the first results from our pilot clinical trial (clinical trials identifier NCT02285192) in 23 patients with uterine or cervical cancer. On the morning of surgery, ¹⁸F-FDG was injected into the cervix, followed by an immediate dynamic PET/CT scan of the pelvis and a delayed 1-h whole body scan. Results: There were 3 (15%) node-positive cases on final pathologic analysis, and all LNs (including one with a focus of only 80 tumor cells) were identified by PLG, except for one node with an 11-mm micrometastasis. There were 2 (10%) false-positive cases with PLG, in which final pathology of the corresponding SLNs was negative for tumor. Conclusion: This first-in-human study of PLG in women with uterine and cervical cancer demonstrates its feasibility and its ability to identify patients with nodal metastases, and warrants further evaluation in additional studies.

Objectives: Radioactive iodine (¹³¹I) therapy may be used to treat thyroid cancer in end-stage renal disease patients who undergo hemodialysis. Because iodine predominantly utilizes renal clearance, treatment management in hemodialysis patients may be problematic, and no formal recommendations on hemodialysis currently exist. This work details our experience with treating thyroid cancer with iodine in chronic renal failure patients who require hemodialysis and details the therapeutic dosimetry results obtained during treatment to ensure that the dose to the bone marrow (BM) was acceptable. Methods: We treated 6 patients in the metabolic radiotherapy unit after thyroid stimulation. Two hemodialysis sessions in the metabolic radiotherapy unit were performed at 42 and 90 hours after radiopharmaceutical administration. BM toxicity was estimated with activity measurements from blood samples and with whole-body measurements that were regularly repeated during hospitalization and measured with a gamma counter. The patients underwent thyroid and hematologic monitoring to assess treatment efficacy and therapeutic toxicity in the short, medium and long term. Results: Whole-body activity was reduced on average by 66.7% [60.1-71.5] after the first dialysis session and by 53.3% [30.4-67.8] after the second. The mean estimated total absorbed dose to the BM was 0.992 Gy for all patients [0.431 – 2.323]. We did not observe any significant hematologic toxicity, and the clinical, biological and ultrasound test results confirmed the success of ablative treatment for the majority of patients. Conclusion: An approximately 30% reduction from the nominal dose in the amount of ¹³¹I activity for hemodialysis patients with thyroid cancer appears to strike an appropriate balance between the absence of BM toxicity and therapeutic efficacy. To avoid overirradiation, we recommend pretherapeutic dosimetry studies for metastatic patients to calculate the amount of activity to be administered as well as dosimetry monitoring during the hemodialysis sessions performed after therapeutic dose administration and under the same conditions.

Rationale: The treatment of choice for insulinomas and focal lesions in congenital hyperinsulinism (CHI) is surgery. However, intra-operative detection can be challenging. This could be overcome with intra-operative fluorescence imaging, which provides real-time lesion detection with a high spatial resolution. Here, a novel method for targeted near-infrared (NIR) fluorescence imaging of glucagon-like peptide 1 receptor (GLP-1R) positive lesions, using the GLP-1 agonist exendin-4, labeled with IRDye800CW, was examined in vitro and in vivo. Methods: A competitive binding assay was performed using Chinese hamster lung (CHL) cells transfected with the GLP-1R. Tracer biodistribution was determined in BALB/c nude mice bearing subcutaneous CHL-GLP-1R xenografts. In vivo NIR fluorescence imaging of CHL-GLP-1R xenografts was performed. Localization of the tracer in the pancreatic islets of BALB/c nude mice was examined using fluorescence microscopy. Laparoscopic imaging was performed to detect the fluorescent signal of the tracer in the pancreas of mini pigs. Results: Exendin-4-IRDye800CW binds the GLP-1R with an IC50 value of 3.96 nM. The tracer accumulates in CHL-GLP-1R xenografts. Subcutaneous CHL-GLP-1R xenografts were visualized using in vivo NIR fluorescence imaging. The tracer accumulates specifically in the pancreatic islets of mice and a clear fluorescent signal was detected in the pancreas of mini pigs. Conclusion: These date provide the first in vivo evidence of the feasibility of targeted fluorescence imaging of GLP-1R positive lesions. Intra-operative lesion delineation using exendin-4-IRDye800CW could benefit open as well as laparoscopic surgical procedures for removal of insulinomas and focal lesions in CHI.

[S-Methyl-¹¹C](±)-7-methoxy-3-(4-(4-(methylthio)phenyl)butyl)-2,3,4,5-tetrahydro-1H-benzo[d]azepin-1-ol (¹¹C-NR2B-SMe) and its enantiomers were synthesized as candidates for imaging the NR2B subunit within the N-methyl-D-aspartate receptor with positron emission tomography (PET). Methods: Brains were scanned with PET for 90 min after intravenous injection of one of the candidate radioligands into rats. To detect any NR2B specific binding of radioligand in brain, various pre-blocking or displacing agents were evaluated for their impact on the PET brain imaging data. Radiometabolites from brain and other tissues were measured ex vivo and in vitro. Results: Each radioligand gave high early whole brain uptake of radioactivity, followed by a brief fast decline and then a slow final decline. ¹¹C-(S)-NR2B-SMe was studied extensively. Ex vivo measurements showed that radioactivity in rat brain at 30 min after radioligand injection was virtually unchanged radioligand. Only less lipophilic radiometabolites appeared in plasma. High-affinity NR2B ligands, Ro-25-6981, ifenprodil, and CO10124, showed increasing preblock of whole brain radioactivity retention with increasing dose (0.01 to 1.25 mg/kg, i.v.). Five 1 antagonists (FTC146, BD1407, F3, F4, and NE100) and four 1 agonists ((+)-pentazocine, (±)-PPCC, PRE-084, (+)-SKF10047) were ineffective preblocking agents, except FTC146 and F4 at high dose. Two potent 1 receptor agonists, TC1 and SA4503, showed dose-dependent preblocking effects in the presence or absence of pharmacological 1 receptor blockade with FTC146. Conclusion: ¹¹C-(S)-NR2B-SMe has adequate NR2B-specific PET signal in rat brain to warrant further evaluation in higher species. TC1 and SA4503 likely have off-target binding to NR2B in vivo.

Quantitative evaluation of radiolabeled Prostate-Specific Membrane Antigen (PSMA) PET scans may be used to monitor treatment response in patients with prostate cancer (PCa). To interpret longitudinal differences in PSMA uptake, the intrinsic variability of tracer uptake in PCa lesions needs to be defined. The aim of this study was to investigate the repeatability of quantitative ¹⁸F-DCFPyL (a second generation ¹⁸F-PSMA-ligand) PET/CT measurements in patients with PCa. Methods: Twelve patients with metastatic PCa were prospectively included, of which 2 were excluded from final analyses. Patients received two whole-body ¹⁸F-DCFPyL PET/CT scans (median dose 317 MBq; uptake time 120 min), within median 4 days (range 1-11 days). After semi-automatic (isocontour-based) tumor delineation, the following lesion-based metrics were derived: Tumor-to-Blood ratio (TBRmean, TBRpeak, and TBRmax), Standardized Uptake Value (SUVmean, SUVpeak, SUV_max, normalized to bodyweight), tumor volume, and total lesion tracer uptake (TLU). Additionally, patient-based Total Tumor Volume (sum of PSMA-positive tumor volumes; TTV) and Total Tumor Burden (sum of all lesion TLUs; TTB) were derived. Repeatability was analyzed using repeatability coefficients (RC) and intra-class correlations (ICC). Additionally, the effect of point spread function (PSF) image reconstruction on the repeatability of uptake metrics was evaluated. Results: In total, 36 ¹⁸F-DCFPyL PET positive lesions were analyzed (up to 5 lesions per patient). RCs of TBRmean, TBRpeak, and TBRmax were 31.8%, 31.7%, and 37.3%, respectively. For SUVmean, SUVpeak, SUV_max the RCs were 24.4%, 25.3% and 31.0%, respectively. All ICC were ≥0.97. Tumor volume delineations were well repeatable, with RC 28.1% for individual lesion volumes and RC 17.0% for TTV. TTB had a RC of 23.2% and 33.4%, when based on SUVmean and TBRmean, respectively. Small lesions (<4.2mL) had worse repeatability for volume measurements. The repeatability of SUVpeak, TLU, and all patient-level metrics were not affected by PSF-reconstruction. Conclusion: ¹⁸F-DCFPyL uptake measurements are well repeatable and can be used for clinical validation in future treatment response assessment studies. Patient-based TTV may be preferred for multicenter studies since its repeatability was both high and robust to different image reconstructions.

Methods that provide rapid access to radiolabeled antibodies are vital in the development of diagnostic and radiotherapeutic agents for positron emission tomography (PET) or radioimmunotherapy. The human hepatocyte growth factor receptor (c-MET) signaling pathway is dysregulated in a number of malignancies including gastric cancer, and is an important biomarker in drug discovery. Here, we used a photoradiochemical approach to produce ⁸⁹Zr-radiolabeled onartuzumab (a monovalent, anti-human c-MET antibody), starting directly from the fully formulated drug (MetMAb). Methods: Simultaneous ⁸⁹Zr-radiolabeling and protein conjugation was performed in one-pot reactions containing ⁸⁹Zr-oxalate, the photoactive chelate DFO-aryl azide (DFO-ArN3) and MetMAb to give ⁸⁹ZrDFO-azepin-onartuzumab. As a control, ⁸⁹ZrDFO-Bn-NCS-onartuzumab was prepared via a conventional two-step process using pre-purified onartuzumab and DFO-Bn-NCS. Radiotracers were purified by using size-exclusion methods and evaluated by radiochromatography. Radiochemical stability was studied in human serum and immunoreactivity was determined by cellular binding assays using MKN-45 gastric carcinoma cells. PET imaging at multiple time points (0–72 h) was performed in female athymic nude mice bearing subcutaneous MKN-45 xenografts. Biodistribution experiments were performed after the final image. Tumor specificity of ⁸⁹ZrDFO-azepin-onartuzumab was assessed by competitive inhibition (blocking) studies. Results: Initial photoradiosynthesis experiments produced ⁸⁹ZrDFO-azepin-onartuzumab in <15 min. with an isolated decay-corrected radiochemical yield (RCY) of 24.8%, a radiochemical purity (RCP) ~90% and a molar activity (Am) of ~1.5 MBq nmol^-1. Reaction optimization improved the radiochemical conversion (RCC) of ⁸⁹ZrDFO-azepin-onartuzumab to 56.9±4.1% (n = 3), with isolated RCYs of 41.2±10.6% (n = 3), and RCPs >90%. Conventional methods produced ⁸⁹ZrDFO-Bn-NCS-onartuzumab with isolated RCY >97%, RCP >97% and Am ~14.0 MBq nmol^-1. Both radiotracers were immunoreactive and stable in human serum. PET imaging and biodistribution studies showed high tumor uptake for both radiotracers. By 72 h, tumor and liver uptake reached 15.37±5.21 %ID g^-1, 6.56±4.03 %ID g^-1, respectively for ⁸⁹ZrDFO-azepin-onartuzumab (n = 4), and 21.38±11.57 %ID g^-1 and 18.84±6.03 %ID g^-1 for ⁸⁹ZrDFO-Bn-NCS-onartuzumab (n = 4). Blocking experiments gave a statistically significant reduction in tumor uptake (6.34±0.47 %ID g^-1) of ⁸⁹ZrDFO-azepin-onartuzumab (n = 4). Conclusion: Experiments demonstrate that photoradiosynthesis is a viable alternative approach for producing ⁸⁹Zr-radiolabeled antibodies direct in protein formulation buffer which reduces protein aggregation and liver uptake.

The impact of prostate specific membrane antigen (PSMA) PET/CT on management of prostate cancer (PCa) patients with biochemical recurrence (BCR) is well-established. However, whether and how PSMA PET/CT affects the management of patients undergoing scans for other clinical indications remains unknown. The goal of this study was to determine the impact of ⁶⁸Ga-PSMA-11 PET/CT on initial and subsequent management decisions in a cohort of PCa patients referred for various indications ("basket trial") excluding the two main classical indications: BCR and presurgical staging. Methods: This was a prospective study of 197 patients that aimed to determine the impact of ⁶⁸Ga-PSMA-11 PET/CT on PCa stage and management. Indications for PSMA PET/CT were: initial staging of non-surgical candidates (30 patients) and re-staging after definitive treatment (n = 168). The re-staging cohort comprised: patients re-staged with known advanced metastatic disease (n = 103), after androgen deprivation therapy only (n = 16), after surgery with serum PSA levels <0.2 ng/ml (n = 13), after radiation therapy (RT) not meeting the Phoenix criteria (n = 22) and after other primary local treatments [i.e. high-intensity focused ultrasound (HIFU), focal laser ablation, cryoablation, hyperthermia or irreversible electroporation] (n = 13). Patients with BCR and candidates for curative surgery were excluded. Impact on management was assessed using pre- and post-PET questionnaires completed by referring physicians, electronic chart review and/or patient telephone encounters. Results: PSMA PET/CT changed disease stage in 135/197 (69%) patients (38% up-stage, 30% down-stage and no changes in stage in 32%). Management was affected in 104/182 (57%) patients. Specifically, PSMA PET/CT impacted management of patients who were re-staged after RT without meeting the Phoenix criteria for BCR, after other definitive local treatments and with advanced metastatic disease in 13/18 (72%), 8/12 (67%) and 59/96 (61%), respectively. Conclusion: PSMA PET/CT has a profound impact on stage and management of PCa patients outside of the two main classical indications (BCR and presurgical staging) across all examined clinical scenarios.

Immune checkpoint blockade represents a promising approach in oncology, showing anti-tumor activities in various cancers. However, although being generally far more well-tolerated than classical cytotoxic chemotherapy, this treatment, too, may be accompanied by considerable side effects and not all patients benefit equally. Therefore, careful patient selection and monitoring of the treatment response is mandatory. At present, checkpoint-specific molecular imaging is increasingly investigated as a tool for patient selection and response evaluation. Here, an overview of the current developments in immune checkpoint imaging is provided.

Purpose: To assess the performance of full dose (FD) positron emission tomography (PET) image synthesis in both image and projection space from low-dose (LD) PET images/sinograms without sacrificing diagnostic quality using deep learning techniques. Methods: Clinical brain PET/CT studies of 140 patients were retrospectively employed for LD to FD PET conversion. 5% of the events were randomly selected from the FD list-mode PET data to simulate a realistic LD acquisition. A modified 3D U-Net model was implemented to predict FD sinograms in the projection-space (PSS) and FD images in image-space (PIS) from their corresponding LD sinograms/images, respectively. The quality of the predicted PET images was assessed by two nuclear medicine specialists using a five-point grading scheme. Quantitative analysis using established metrics including the peak signal-to-noise ratio (PSNR), structural similarity index metric (SSIM), region-wise standardized uptake value (SUV) bias, as well as first-, second- and high-order texture radiomic features in 83 brain regions for the test and evaluation dataset was also performed. Results: All PSS images were scored 4 or higher (good to excellent) by the nuclear medicine specialists. PSNR and SSIM values of 0.96 ± 0.03, 0.97 ± 0.02 and 31.70 ± 0.75, 37.30 ± 0.71 were obtained for PIS and PSS, respectively. The average SUV bias calculated over all brain regions was 0.24 ± 0.96% and 1.05 ± 1.44% for PSS and PIS, respectively. The Bland-Altman plots reported the lowest SUV bias (0.02) and variance (95% CI: -0.92, +0.84) for PSS compared with the reference FD images. The relative error of the homogeneity radiomic feature belonging to the Grey Level Co-occurrence Matrix category was -1.07 ± 1.77 and 0.28 ± 1.4 for PIS and PSS, respectively Conclusion: The qualitative assessment and quantitative analysis demonstrated that the FD PET prediction in projection space led to superior performance, resulting in higher image quality and lower SUV bias and variance compared to FD PET prediction in the image domain.

Objective: To develop a novel approach to generate individual maps of white matter (WM) innate immune cell activation using ¹⁸F-DPA-714 translocator protein (TSPO) positron emission tomography (PET), and to explore the relationship between these maps and individual trajectories of disability worsening in patients with multiple sclerosis (MS). Methods: Patients with MS (n = 37), whose trajectories of disability worsening over the 2 years preceding study entry were calculated, and healthy controls (n = 19) underwent magnetic resonance magnetic and ¹⁸F-DPA-714 PET. A threshold of significant activation of ¹⁸F-DPA-714 binding was calculated with a voxel-wise randomized permutation-based comparison between patients and controls, and used to classify each WM voxel in patients as characterized by a significant activation of innate immune cells (DPA+) or not. Individual maps of innate immune cell activation in the WM were employed to calculate the extent of activation in WM regions-of-interests and to classify each WM lesion as "DPA-active", "DPA-inactive" or "unclassified". Results: Compared with the WM of healthy controls, patients with MS had a significantly higher percentage of DPA+ voxels in the normal-appearing WM, (NAWM in patients=24.9±9.7%; WM in controls=14.0±7.8%, p<0.001). In patients with MS, the percentage of DPA+ voxels showed a significant increase from NAWM, to perilesional areas, T2 hyperintense lesions and T1 hypointense lesions (38.1±13.5%, 45.0±17.9%, and 51.9±22.9%, respectively, p<0.001). Among the 1379 T2 lesions identified, 512 were defined as DPA-active and 258 as DPA-inactive. A higher number of lesions classified as DPA-active (OR=1.13, P = 0.009), a higher percentage of DPA+ voxels in the NAWM (OR=1.16, P = 0.009) and in T1-spin-echo lesions (OR=1.06, P = 0.036), were significantly associated with a retrospective more severe clinical trajectory in patients with MS. Conclusion: A more severe trajectory of disability worsening in MS is associated with an innate immune cells activation inside and around WM lesions. ¹⁸F-DPA-714 PET may provide a promising biomarker to identify patients at risk of severe clinical trajectory.

Acidosis is a key driver for many diseases, including cancer, sepsis, and stroke. The spatiotemporal dynamics of dysregulated pH across disease remains elusive and current diagnostic strategies do not provide localization of pH alterations. We sought to explore if PET imaging using hydrophobic cyclic peptides that partition into the cellular membrane at low extracellular pH (denoted as "pHLIC") can permit accurate in vivo visualization of acidosis. Methods: Acid-sensitive cyclic peptide c[E4W5C] pHLIC was conjugated to bifunctional maleimide-NO2A and radiolabeled with copper-64 (t1/2 = 12.7 h). C57BL/6J mice were administered LPS (15 mg/kg) or saline (vehicle) and serially imaged with [⁶⁴Cu]Cu-c[E4W5C] over 24 h. Ex vivo autoradiography was performed on resected brain slices and subsequently stained with cresyl violet to enable high-resolution spatial analysis of tracer accumulation. A non- pH-sensitive cell-penetrating control peptide (c[R4W5C]) was used to confirm specificity of [⁶⁴Cu]Cu-c[E4W5C]. CD11b (macrophage/microglia) and TMEM119 (microglia) immunostaining was performed to correlate extent of neuroinflammation with [⁶⁴Cu]Cu-c[E4W5C] PET signal. Results: [⁶⁴Cu]Cu-c[E4W5C] radiochemical yield and purity was >95% and >99% respectively, with molar activity >0.925 MBq/nmol. Significantly increased [⁶⁴Cu]Cu-c[E4W5C] uptake was observed in LPS-treated mice (vs. vehicle) within peripheral tissues including blood, lungs, liver, and small intestines (P < 0.001-0.05). Additionally, there was significantly increased [⁶⁴Cu]Cu-c[E4W5C] uptake in the brains of LPS-treated animals. Autoradiography confirmed increased uptake in the cerebellum, cortex, hippocampus, striatum, and hypothalamus of LPS-treated mice (vs. vehicle). Immunohistochemical (IHC) analysis revealed microglial/macrophage infiltrate, suggesting activation in brain regions containing increased tracer uptake. [⁶⁴Cu]Cu-c[R4W5C] demonstrated significantly reduced uptake in the brain and periphery of LPS mice compared to the acid-mediated [⁶⁴Cu]Cu-c[E4W5C] tracer. Conclusion: Here, we demonstrate that a pH-sensitive PET tracer specifically detects acidosis in regions associated with sepsis-driven pro-inflammatory responses. This study suggests that [⁶⁴Cu]Cu-pHLIC is a valuable tool to noninvasively assess acidosis associated with both central and peripheral innate immune activation.

Respiratory motion during the CT and PET parts of a PET/CT scan leads to imperfect alignment of anatomical features seen by the two modalities. In this work, we concentrate on the effects of motion during CT. We propose a novel approach for improving the alignment. Methods: Respiratory waveform data were gathered during the CT and PET parts of 28 PET/CT scans of cancer patients with 40 lesions up to 3 cm size in the lung or upper abdomen. PET list-mode data were reconstructed by three reconstruction methods: PET/static, PET/EX or end of expiration (OncoFreeze), and a novel PET/matched method that used both waveforms. The three methods were compared. The distance between tumor positions in PET and CT were characterized in visual interpretation by physicians as well as quantitatively. Tumor standardized uptake values (SUV_max and SUVpeak) were determined relative to SUV based on the static method. Image noise was evaluated in the liver and compared to PET/static. Results: In visual interpretation, the rate of good alignment was 13/21, 13/23 and 18/21 for PET/static, PET/EX and PET/matched methods, respectively, and the mean PET-CT distances were 3.5, 5.1 and 2.8 mm. In visual comparison with PET/EX, the rate of good alignment was increased in 1/10 and 7/10 cases for PET/static and PET/matched. SUV_max was on average 21% higher than PET/static when either PET/EX or PET/matched was used. SUVpeak was 12% higher. Image noise in the liver was 15% higher than static for the PET/EX method, and 40% higher for PET/matched; that is, noise was much lower than in gated PET. Conclusion: Acquiring respiratory waveforms both in PET (as in the current state of the art) and in CT (an unusual key step in this approach) has the potential to improve the alignment of PET and CT images. A proposed method for using this information was tested. Improved alignment was demonstrated.

Studies demonstrate that the investigational ⁶⁴Cu-DOTATATE radiopharmaceutical may provide diagnostic and logistical benefits over available imaging agents for patients with somatostatin receptor (SSTR)-positive neuroendocrine tumors (NETs). Accordingly, we aimed to prospectively determine the lowest dose of ⁶⁴Cu-DOTATATE that facilitates diagnostic quality scans and evaluated the diagnostic performance and safety in a phase III study of patients with SSTR-expressing NETs. Methods: A dose-ranging study was conducted in 12 patients divided into 3 dose groups (111 MBq [3.0 mCi], 148 MBq [4.0 mCi], and 185 MBq [5.0 mCi] ± 10%) to determine the lowest dose of ⁶⁴Cu-DOTATATE that produced diagnostic quality PET/CT images. Using the ⁶⁴Cu-DOTATATE dose identified in the dose-ranging study, 3 independent nuclear medicine physicians who were blinded to all clinical information read PET/CT scans from 21 healthy volunteers and 42 NET-positive patients to determine those with "Disease" and "No Disease," as well as "Localized" versus "Metastatic" status. Blinded-reader evaluations were compared to a patient-specific standard of truth (SOT), which was established by an independent oncologist who used all previously available pathology, clinical, and conventional imaging data. Diagnostic performance calculated for ⁶⁴Cu-DOTATATE included sensitivity, specificity, negative predictive value, positive predictive value, and accuracy. Inter- and intra-reader reliability, as well as ability to differentiate between localized and metastatic disease, was also determined. Adverse events (AEs) were recorded from ⁶⁴Cu-DOTATATE injection through 48 hours post-injection. Results: The dose-ranging study identified 148 MBq (4.0 mCi) as the optimal dose to obtain diagnostic quality PET/CT images. Following database lock, diagnostic performance from an initial majority read of the 3 independent readers showed a significant 90.9% sensitivity (P = 0.0042) and 96.6% specificity (P < 0.0001) for detecting NETs, which translated to a 100.0% sensitivity and 96.8% specificity after correcting for an initial SOT misread. Excellent inter- and intra-reader reliability, as well as ability to distinguish between localized and metastatic disease, was also noted. No AEs were related to ⁶⁴Cu-DOTATATE, and no serious AEs were observed. Conclusion: ⁶⁴Cu-DOTATATE PET/CT is a safe imaging technique that provides high-quality and accurate images at a dose of 148 MBq (4.0 mCi) for the detection of somatostatin-expressing NETs.

Galectins are carbohydrate-binding proteins overexpressed in bladder cancer (BCa) cells. Dendritic galactose moieties have a high affinity for galectin-expressing tumor cells. We radiolabeled a dendritic galactose carbohydrate with fluorine-18 – ¹⁸F-labeled galactodendritic unit 4 – and examined its potential in imaging urothelial malignancies. Methods: The ¹⁸F-labeled 1st generation galactodendritic unit 4 was obtained from its tosylate precursor. We conducted in vivo studies in galectin-expressing UMUC3 orthotopic BCa model to determine the ability of ¹⁸F-labeled galactodendritic unit 4 to image BCa. Results: Intravesical administration of ¹⁸F-labeled galactodendritic unit 4 allowed specific accumulation of the carbohydrate radiotracer in galectin-1 overexpressing UMUC3 orthotopic tumors when imaged with PET. The ¹⁸F-labeled galactodendritic unit 4 was not found to accumulate in non-tumor murine bladders. Conclusion: The ¹⁸F-labeled galactodendritic unit 4 and similar analogs may be clinically relevant and exploitable for PET imaging of galectin-1 overexpressing bladder tumors.

Peptide receptor radiotherapy using ¹⁷⁷Lu-labeled somatostatin ligand analogs is a well-established treatment for neuroendocrine tumors (NET), with ¹⁷⁷Lu-DOTATATE having acquired marketing authorization in Europe and the USA. The investigation of the pharmacokinetics of those radiopharmaceuticals in vivo in humans is crucial for personalized treatment management and understanding of treatment effects. It requires input data on the in vivo stability of the radiopharmaceuticals in blood and plasma. The work presented here is devoted to the investigation of in vivo stability of ¹⁷⁷Lu-DOTATATE in humans affected by NET. Unexpectedly, fast metabolism of the radiopharmaceutical was observed, with fraction of intact ¹⁷⁷Lu-DOTATATE in plasma decreasing rapidly to 23±5% (mean ± SD) at 24 h and 1.7±0.9% at 96 h after injection.