32 Background: Multi-detector cadmium-zinc-telluride (CZT) based whole-body digital SPECT/CT is a new generation of imaging system. We aim to assess the clinical utility of rapid post-therapy whole-body SPECT/CT scan in evaluating early treatment response of 177Lu-PSMA-617 treatment. Methods: We retrospectively reviewed patients with progressive metastatic castration resistant prostate cancer (mCRPC) who were treated with at least two cycles of 177Lu-PSMA-617 at our institution from June 2022 to June 2023. Post-therapy whole-body digital SPECT/CT (GE StarGuide) was performed from vertex to mid-thigh at 1-2 hours after 177Lu-PSMA-617 infusion. Post-therapy SPECT/CT images were quantified with MIM software. Lu177-PSMA positive lesions were delineated with liver parenchyma uptake as cut-off. Lu-PSMA positive total tumor volume (Lu-TTV), tumor SUVmax and SUVmean were obtained. Post-therapy SPECT/CT image after cycle 1 was used as baseline for comparison with SPECT/CT after cycle 2 and 3. Overall survival, PSA progression free survival (PSA-PFS) as defined by PCWG3 and PSA decline > 50% from baseline (PSA50) at any time after treatment were measured. Changes in post-therapy SPECT/CT were correlated with clinical outcomes to assess quantitative SPECT/CT as a tool for early treatment response. Analyses were performed with SPSS. Results: A total of 56 patients (76±8, mean ± SD, range 60-93 years old) who were imaged with at least 2 post-therapy SPECT/CT were included in the analysis. Post-therapy whole body SPECT/CT was acquired in ~12 mins. All scanned patients tolerated the rapid whole-body SPECT/CT very well. With median follow up of 10 months, median PSA-PFS was 5.0 months (range 1.0-15 months), 33 of 56 patients (58.9%) achieved PSA50 at any time after treatment, and 42 of 56 patients (75%) were alive at data cutoff. Quantitative analysis of SPECT/CT images showed that 36 of 56 patients (64%) had a >30% decrease in Lu-TTV on early follow-up post-therapy SPECT/CT after cycle 2 or 3. Kaplan-Meier survival analysis showed that a >30% decrease in Lu-TTV was associated with longer overall survival (median not reached vs 6 months, P = 0.008) and longer PSA-PFS (6 months vs 1 months, P < 0.001). Decrease in SUVmax or SUVmean, however, was not associated with PSA-PFS or overall survival. Conclusions: Rapid post-therapy whole-body digital SPECT/CT was well tolerated in post-therapy SPECT/CT imaging following 177Lu-PSMA-617 treatment. Quantitation of post-therapy SPECT/CT may be useful in evaluating early treatment response of 177Lu-PSMA-617. Prospective validation and larger patient cohorts are needed to further elucidate the role of post-therapy SPECT/CT imaging in guiding patient management in 177Lu-PSMA-617 therapy.

Objectives:This practice parameter was revised collaboratively by the American College of Radiology (ACR), the American College of Nuclear Medicine, the American Radium Society, the American Society for Radiation Oncology, and the Society of Nuclear Medicine and Molecular Imaging. The document is intended to serve as a resource for appropriately trained and licensed physicians who perform therapeutic procedures with unsealed sources, referred to in the document using the more inclusive terminology of radiopharmaceuticals, for which a written directive is required for authorized users under NRC 10 CFR 35.300.Methods:This practice parameter was developed according to the process described under the heading The Process for Developing ACR Practice Parameters and Technical Standards on the ACR website (https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards) by the Committee on Practice Parameters-Radiation Oncology of the ACR Commission on Radiation Oncology in collaboration with the American Radium Society.Results:This practice parameter addresses the overall role of the applicable physician-authorized user, Qualified Medical Physicist, and other specialized personnel involved in the delivery of radiopharmaceutical therapy. Therapeutic radiopharmaceuticals include those administered as elemental radioactive isotopes (radionuclides) or the radioactive element incorporated into a targeting molecule (ligand) by one or more chemical bonds. This document provides guidance regarding general principles of radionuclide therapies and indications of various alpha, beta, gamma, and mixed emission agents with references to several recent practice parameters on new and commonly performed radiopharmaceutical therapies.Conclusion:This document addresses clinical circumstances, elements of available agents, and the qualifications and responsibilities of various members of the radiation care team, specifications of consultation and other clinical documentation, post-therapy follow-up, radiation safety precautions, elements of quality control and improvement programs, infection control, and patient education to ensure optimal patient care and safety when utilizing radiopharmaceuticals.

Lutetium-177 [177Lu]Lu-PSMA-617 radioligand therapy (RLT) represents a significant advancement for metastatic castration-resistant prostate cancer (mCRPC), demonstrating improvements in radiographic progression free survival (rPFS) and overall survival (OS) with a low rate of associated side effects. Currently, most post-therapy SPECT/CT is conducted at 24 h after infusion. This study examines the clinical utility of a next-generation multi-detector Cadmium-Zinc-Telluride (CZT) SPECT/CT system (StarGuide) in same-day post-infusion assessment and early treatment response to [177Lu]Lu-PSMA-617. In this retrospective study, 68 men with progressive mCRPC treated with [177Lu]Lu-PSMA-617 at our center from June 2022 to June 2023 were evaluated. Digital whole-body SPECT/CT imaging was performed after [177Lu]Lu-PSMA-617infusion (mean ± SD: 1.8 ± 0.6 h, range 1.1–4.9 h). Quantitative analysis of [177Lu]Lu-PSMA-617 positive lesions was performed in patients who underwent at least 2 post-therapy SPECT/CT, using liver parenchyma uptake as reference. Metrics including [177Lu]Lu-PSMA-617 positive total tumor volume (Lu-TTV), SUVmax and SUVmean were calculated. These quantitative metrics on post-infusion SPECT/CT images after cycles 1, 2 and 3 were correlated with overall survival (OS), prostate specific antigen-progression free survival (PSA-PFS) as defined by prostate cancer working group 3 (PCWG3), and PSA decrease over 50

Peptide receptor radionuclide therapy (PRRT) consists of administrating a radiolabeled octreotide derivative that targets somatostatin receptors present on the cell membrane of neuroendocrine tumor cells. Although PRRT was initially performed with 90Y-peptides, currently 177Lu-peptides represent the predominant form of treatment. PRRT results in significant tumor and symptomatic control in patients. Like with other available systemic therapies, responses are relatively short-lived. Several new peptides and strategies to improve the efficacy and tolerability of PRRT have been proposed. A critical step is individualizing treatments based on specific dosimetric estimates for the tumor and normal organs, and determining tissue radiosensitivity.

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare malignancies that arise from secretory endocrine cells of the gastroenteropancreatic system. Clinical outcomes have improved for patients with GEP-NETs due to the development and recent FDA approval of 177Lutetium DOTATATE. However, the response of brain metastases from GEP-NETs from 177Lutetium DOTATATE is unreported. We present the case of an 81-year-old man with low-grade small bowel GEP-NET with liver and brain metastases treated with a total of six cycles of 177Lutetium DOTATATE. With over three years of follow-up from his initial treatment, his brain metastases have had complete or partial responses, with no need for brain radiotherapy or radiosurgery.

e17015 Background: PSMA PET has been widely adopted in restaging of prostate cancer at biochemical recurrence. We assess the clinical utility of quantitative parameters on 18 F-DCFPyL PET/CT at biochemical recurrence and their association with the subsequent biochemical progression free survival (bPFS). Methods: This is a retrospective image analysis and longitudinal follow up of a prospective study evaluating 18 F-DCFPyL PET in prostate cancer patients with biochemical recurrence after primary definitive treatment at Stanford Hospital. The 18 F-DCFPyL PET images were quantitatively analyzed automatically by the aPROMISE application, a semi-automated analysis and structured reporting of PSMA PET/CT. aPROMISE uses deep learning to segment detailed anatomical information from the CT images and uses this information in combination with the PET image to detect and quantify candidates for prostate cancer lesions. The reader works in tandem with the software to vet the final list of lesions, from which the quantitative assessments and final report is created automatically. Based on the Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria. SUVmean, PSMA positive total tumor volume (PSMAttv) and aPSMA scores, a quantitative score for tumor burden measuring the interaction of tumor volume and uptake stratified by local tumors (aPSMA-miT), regional lymph nodes (aPSMA-miN) and distant metastases (aPSMA-miMa for extrapelvic metastases, miMb for bone metastases and miMc for other organ metastases) were obtained based on the miTNM classification. The association of these quantitative parameters with the subsequent bPFS was evaluated. Results: 134 patients (age 70.1 ± 7.6, range 51 -91 years; PSA 13.9 ± 98.5, range 0.12 – 1126 ng/mL) were included in the quantitative image analysis. aPROMISE detected nodal and/or bone metastases in 94 of 134 patients (70%) and only 12 of 134 patients (9%) had visceral disease. With median follow up of 37 months, 66 of 134 patients (49%) have progressed again biochemically after treatment. The bPSF was 25.8 ± 15.1 months. Quantitative analysis of 18 F-DCFPyL PET found that the subsequent bPFS is significantly associated with aPSMA-miMb ( P < 0.001), PSMAttv ( P < 0.001), aPSMA-miN ( P < 0.01), aPSMA-miMa ( P < 0.05) but not with SUVmean or aPSMA-miMc. Conclusions: Total and anatomically contextualized quantitative image analysis of 18 F-DCFPyL PET/CT at biochemical recurrence may be useful in predicting the subsequent bPFS. Studies in larger patient cohort is necessary to validate these findings. Given many patients were treated based on lesions found on 18 F-DCFPyL PET/CT, clinical implication of this findings remains to be elucidated.

To evaluate the feasibility of using the StarGuide (General Electric Healthcare, Haifa, Israel), a new generation multi-detector cadmium-zinc-telluride (CZT)-based SPECT/CT, for whole-body imaging in the setting of post-therapy imaging of 177Lu-labeled radiopharmaceuticals. Thirty-one patients (34–89 years old; mean ± SD, 65.5 ± 12.1) who were treated with either 177Lu-DOTATATE (n=17) or 177Lu-PSMA617 (n=14) as part of standard of care were scanned post-therapy with the StarGuide; some were also scanned with the standard GE Discovery 670 Pro SPECT/CT. All patients had either 64Cu-DOTATATE or 18F-DCFPyL PET/CT prior to first cycle of therapy for eligibility check. The detection/targeting rate (lesion uptake greater than blood pool uptake) of large lesions meeting RECIST 1.1 size criteria on post-therapy StarGuide SPECT/CT was evaluated and compared to the standard design GE Discovery 670 Pro SPECT/CT (when available) and pre-therapy PET by two nuclear medicine physicians with consensus read. This retrospective analysis identified a total of 50 post-therapy scans performed with the new imaging protocol from November 2021 to August 2022. The StarGuide system acquired vertex to mid-thighs post-therapy SPECT/CT scans with 4 bed positions, 3 min/bed and a total scan time of 12 min. In comparison, the standard GE Discovery 670 Pro SPECT/CT system typically acquires images in 2 bed positions covering the chest, abdomen, and pelvis with a total scan time of 32 min. The pre-therapy 64Cu-DOTATATE PET takes 20 min with 4 bed positions on GE Discovery MI PET/CT, and 18F-DCFPyL PET takes 8–10 min with 4–5 bed positions on GE Discovery MI PET/CT. This preliminary evaluation showed that the post-therapy scans acquired with faster scanning time using StarGuide system had comparable detection/targeting rate compared to the Discovery 670 Pro SPECT/CT system and detected large lesions defined by RECIST criteria on the pre-therapy PET scans. Fast acquisition of whole-body post-therapy SPECT/CT is feasible with the new StarGuide system. Short scanning time improves the patients’ clinical experience and compliance which may lead to increased adoption of post-therapy SPECT. This opens the possibility to offer imaged-based treatment response assessment and personalized dosimetry to patients referred for targeted radionuclide therapies.

'See what you treat and treat what you see, at a molecular level', could be the motto of theranostics. The concept implies diagnosis (imaging) and treatment of cells (usually cancer) using the same molecule, thus guaranteeing a targeted cytotoxic approach of the imaged tumor cells while sparing healthy tissues. As the brilliant late Sam Gambhir would say, the imaging agent acts like a 'molecular spy' and reveals where the tumoral cells are located and the extent of disease burden (diagnosis). For treatment, the same 'molecular spy' docks to the same tumor cells, this time delivering cytotoxic doses of radiation (treatment). This duality represents the concept of a 'theranostic pair', which follows the scope and fundamental principles of targeted precision and personalized medicine. Although the term theranostic was noted in medical literature in the early 2000s, the principle is not at all new to nuclear medicine. The first example of theranostic dates back to 1941 when Dr. Saul Hertz first applied radioiodine for radionuclide treatment of thyroid cells in patients with hyperthyroidism. Ever since, theranostics has been an integral element of nuclear medicine and molecular imaging. The more we understand tumor biology and molecular pathology of carcinogenesis, including specific mutations and receptor expression profiles, the more specific these 'molecular spies' can be developed for diagnostic molecular imaging and subsequent radionuclide targeted therapy (radiotheranostics). The appropriate selection of the diagnostic and therapeutic radionuclide for the 'theranostic pair' is critical and takes into account not only the type of cytotoxic radiation emission, but also the linear energy transfer (LET), and the physical half-lives. Advances in radiochemistry and radiopharmacy with new radiolabeling techniques and chelators are revolutionizing the field. The landscape of cytotoxic systemic radionuclide treatments has dramatically expanded through the past decades thanks to all these advancements. This article discusses present and promising future theranostic applications for various types of diseases such as thyroid disorders, neuroendocrine tumors (NET), pediatric malignancies, and prostate cancer (PC), and provides an outlook for future perspectives.

Background Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin receptor (SSR) analogs is now an established systemic treatment for neuroendocrine tumors (NET). However, more short- and long-term data about renal and hepatotoxicity is needed. Here we present our experience in this clinical scenario. Methods Eighty-six patients with progressive SSR-expressing malignancies underwent PRRT with Lu-177 Dotatate and were followed up for up to 2 years. Laboratory tests were done 1 week before each cycle and every 2 months at follow-up. Hepatic and renal toxicity was determined based on NCI CTCAE V5.0. Results 55/86 (64%) patients completed all 4 cycles of PRRT; 18/86 (20.9%) are currently being treated; 13/86 (15.1%) had to discontinue PRRT: 4/13 (31%) due to hematologic toxicity, 9/13 (69%) due to non-PRRT-related comorbidities. Out of the patients who finished treatment, only transient grade 2 toxicities were observed during PRRT: hypoalbuminemia in 5.5% (3/55), and renal toxicity (serum creatinine and estimated glomerular filtration rate) in 1.8% (1/55). No grade 3 or 4 liver and renal toxicity occurred. Patients presenting with impaired liver or renal function prior to PRRT, either improved or had stable findings. No deterioration was observed. Conclusion Peptide receptor radionuclide therapy does not have a negative impact on liver and renal function, even in patients with pre-existing impaired parameters. No grade 3 or 4 hepatic or renal toxicity was identified. Only transient grade 2 hypoalbuminemia in 5.5% and nephrotoxicity in 1.8% of patients were seen during PRRT.

One of the great strengths of positron emission tomography (PET) is its ability to quantitatively image a wide array of molecular targets for disease evaluation. However, multi-tracer PET imaging is hindered because current technology permits only one PET tracer to be imaged at a time. The aim of this study was to develop a deep learning system that uses a PET image obtained with one tracer to predict a synthetic PET image of a different tracer without having to actually inject the second tracer. Deep neural networks were designed to generate synthetic 3 $$'$$ -deoxy-3 $$'$$ -[ $$^{18}$$ F]-fluorothymidine ( $$^{18}$$ F-FLT) PET images from 3,4-dihydroxy-6-[ $$^{18}$$ F]-fluoro-L-phenylalanine ( $$^{18}$$ F-FDOPA) PET and magnetic resonance imaging scans of nineteen patients with glioblastoma. Here, we show that the proposed image synthesis method closely predicts the ground truth $$^{18}$$ F-FLT PET images (MAE = 0.024 ± 0.004, SSIM = 0.832 ± 0.035, PSNR = 27.521 ± 1.606). Moreover, a blinded image evaluation by three nuclear medicine physicians determined that the synthetic images were rated significantly better on spatial resolution (p < 0.015), image noise (p < 0.001) and overall image quality (p < 0.0001) than the true PET images. This study offers a new strategy for multi-tracer PET imaging using machine learning and reduces radiation dose to the patient by at least 50%.

ABSTRACTPeptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE has shown great treatment efficacy in patients with well-differentiated metastatic neuroendocrine tumors and a metastatic size reduction of ~20% for metastatic lesions <3 cm in size. We present a 66-year-old man with pancreatic neuroendocrine carcinoma, who had a rapidly growing metastatic nodal conglomerate, which measured close to 10 cm in size. After only 2 cycles of PRRT with 177Lu-DOTATATE, the nodal conglomerate had a striking size reduction greater than 75%. This case highlights the potential efficacy of PRRT with 177Lu-DOTATATE for treatment of aggressive neuroendocrine neoplasms.

Background: The goal of this study is to demonstrate the feasibility of [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) for non-invasive visualization of muscular, neurovascular, and skin changes secondary to complex regional pain syndrome (CRPS). Methods: Seven adult patients with CRPS in the lower extremity and seven healthy adult controls participated in our [18F]FDG PET/MRI study. All participants received whole-body PET/MRI scans one hour after the injection of 10mCi [18F]FDG. Resulting PET/MRI images were reviewed by two radiologists. Metabolic and anatomic abnormalities identified, were grouped into muscular, neurovascular, and skin lesions. The [18F]FDG uptake of each lesion was compared with that of corresponding areas in controls using a Mann-Whitney U-test. Results: On PET images, muscular, neurovascular, and skin abnormalities were found in 5, 4 and 2 patients, respectively. However, on MRI images, no muscular abnormalities were detected. Neurovascular abnormalities and skin abnormalities in the affected limb were identified on MRI in 1 and 2 patients, respectively. The difference in [18F]FDG uptake between the patients and the controls was significant in muscle (p = 0.018) and neurovascular bundle (p = 0.0005).Conclusions: The increased uptake of [18F]FDG in the symptomatic areas likely reflects the increased metabolism due to the inflammatory response causing pain. Therefore, our approach combining metabolic ([18F]FDG PET) and anatomic (MRI) imaging may offer non-invasive monitoring of the distribution and progression of inflammatory changes associated with CRPS. Trial registration: ClinicalTrials.gov, NCT03195270. Registered 19 June 2017 - Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03195270

Visual Abstract Targeting of lesions seen on multiparametric MRI (mpMRI) improves prostate cancer (PC) detection at biopsy. However, 20%–65% of highly suspicious lesions on mpMRI (PI-RADS [Prostate Imaging-Reporting and Data System] 4 or 5) are false-positives (FPs), while 5%–10% of clinically significant PC (csPC) are missed. Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptors (GRPRs) are both overexpressed in PC. We therefore aimed to evaluate the potential of 68Ga-PSMA11 and 68Ga-RM2 PET/MRI for biopsy guidance in patients with suspected PC. Methods: A highly selective cohort of 13 men, aged 58.0 ± 7.1 y, with suspected PC (persistently high prostate-specific antigen [PSA] and PSA density) but negative or equivocal mpMRI results or negative biopsy were prospectively enrolled to undergo 68Ga-PSMA11 and 68Ga-RM2 PET/MRI. PET/MRI included whole-body and dedicated pelvic imaging after a delay of 20 min. All patients had targeted biopsy of any lesions seen on PET followed by standard 12-core biopsy. The SUVmax of suspected PC lesions was collected and compared with gold standard biopsy. Results: PSA and PSA density at enrollment were 9.8 ± 6.0 (range, 1.5–25.5) ng/mL and 0.20 ± 0.18 (range, 0.06–0.68) ng/mL2, respectively. Standardized systematic biopsy revealed a total of 14 PCs in 8 participants: 7 were csPC and 7 were nonclinically significant PC (ncsPC). 68Ga-PSMA11 identified 25 lesions, of which 11 (44%) were true-positive (TP) (5 csPC). 68Ga-RM2 showed 27 lesions, of which 14 (52%) were TP, identifying all 7 csPC and also 7 ncsPC. There were 17 concordant lesions in 11 patients versus 14 discordant lesions in 7 patients between 68Ga-PSMA11 and 68Ga-RM2 PET. Incongruent lesions had the highest rate of FP (12 FP vs. 2 TP). SUVmax was significantly higher for TP than FP lesions in delayed pelvic imaging for 68Ga-PSMA11 (6.49 ± 4.14 vs. 4.05 ± 1.55, P = 0.023) but not for whole-body images, nor for 68Ga-RM2. Conclusion: Our results show that 68Ga-PSMA11 and 68Ga-RM2 PET/MRI are feasible for biopsy guidance in suspected PC. Both radiopharmaceuticals detected additional clinically significant cancers not seen on mpMRI in this selective cohort. 68Ga-RM2 PET/MRI identified all csPC confirmed at biopsy.

Objectives: Ga-68-PSMA11 PET/CT is excellent for evaluating biochemically recurrent prostate cancer (BCR PC). Here, we compared the positivity rates of dual-time point imaging using a PET/CT scanner (DMI) with silicon photomultiplier (SiPM) detectors and a PET/CT scanner (D690) with photomultiplier tubes (PMT), in patients with BCR PC. Methods: Fifty-eight patients were prospectively recruited and randomized to receive scans on DMI followed by D690 or vice-versa. Images from DMI were reconstructed using the block sequential regularized expectation maximization (BSREM) algorithm and images from D690 were reconstructed using ordered subset expectation maximization (OSEM), according to the vendor's recommendations. Two readers independently reviewed all images in randomized order, recorded the number and location of lesions, as well as standardized uptake value (SUV) measurements. Results: Twenty-eight patients (group A) had DMI as first scanner followed by D690, while 30 patients (group B) underwent scans in reversed order. Mean PSA was 30 +/- 112.9 (range 0.3-600.66) ng/mL for group A and 41.5 +/- 213.2 (range 0.21-1170) ng/mL for group B (P = 0.796). The positivity rate in group A was 78.6% (22/28 patients) vs. 73.3% (22/30 patients) in group B. Although the performance of the two scanners was equivalent on a per-patient basis, DMI identified 5 additional sites of suspected recurrent disease when used as first scanner. The second scan time point did not reveal additional abnormal uptake. Conclusions: The delayed time point in Ga-68-PSMA11 PET/CT did not show a higher positivity rate. SiPM-based PET/CT identified additional lesions. Further studies with larger cohorts are needed to confirm these results.

Visual Abstract Focal therapy for localized prostate cancer (PC) using high-intensity focused ultrasound (HIFU) is gaining in popularity as it is noninvasive and associated with fewer side effects than standard whole-gland treatments. However, better methods to evaluate response to HIFU ablation are an unmet need. Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptors are both overexpressed in PC. In this study, we evaluated a novel approach of using both 68Ga-RM2 and 68Ga-PSMA11 PET/MRI in each patient before and after HIFU to assess the accuracy of target tumor localization and response to treatment. Methods: Fourteen men, 64.5 ± 8.0 y old (range, 48–78 y), with newly diagnosed PC were prospectively enrolled. Before HIFU, the patients underwent prostate biopsy, multiparametric MRI, 68Ga-PSMA11, and 68Ga-RM2 PET/MRI. Response to treatment was assessed at a minimum of 6 mo after HIFU with prostate biopsy (n = 13), as well as 68Ga-PSMA11 and 68Ga-RM2 PET/MRI (n = 14). The SUVmax and SUVpeak of known or suspected PC lesions were collected. Results: Pre-HIFU biopsy revealed 18 cancers, of which 14 were clinically significant (Gleason score ≥ 3 + 4). Multiparametric MRI identified 18 lesions; 14 of them were at least score 4 in the Prostate Imaging–Reporting and Data System. 68Ga-PSMA11 and 68Ga-RM2 PET/MRI each showed 23 positive intraprostatic lesions; 21 were congruent in 13 patients, and 5 were incongruent in 5 patients. Before HIFU, 68Ga-PSMA11 identified all target tumors, whereas 68Ga-RM2 PET/MRI missed 2 tumors. After HIFU, 68Ga-RM2 and 68Ga-PSMA11 PET/MRI both identified clinically significant residual disease in 1 patient. Three significant ipsilateral recurrent lesions were identified, whereas 1 was missed by 68Ga-PSMA11. The pretreatment level of prostate-specific antigen decreased significantly after HIFU, by 66%. Concordantly, the pretreatment SUVmax decreased significantly after HIFU for 68Ga-PSMA11 (P = 0.001) and 68Ga-RM2 (P = 0.005). Conclusion: This pilot study showed that 68Ga-PSMA11 and 68Ga-RM2 PET/MRI identified the target tumor for HIFU in 100% and 86% of cases, respectively, and accurately verified response to treatment. PET may be a useful tool in the guidance and monitoring of treatment success in patients receiving focal therapy for PC. These preliminary findings warrant larger studies for validation.

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Rationale and Objectives: High-grade gastroenteropancreatic neuroendocrine neoplasms (G3 GEP-NENs) are pathologically classified into well differentiated neuroendocrine tumors (G3 NETs) and poorly differentiated neuroendocrine carcinomas (G3 NECs). Using a novel parameter, we examined the prognostic value of F-18-FDG and Ga-68-DOTATATE PET/CT quantification in comparison to pathologic assessment in G3 GEP-NENs. Materials and Methods: A total of 31 patients with G3 GEP-NENs were reviewed. For each patient, the SUVmax on 18F-FDG and 68Ga-DOTATATE PET/CT were used to calculate the FDG-DOTATATE-Z (FDZ) score: a continuous parameter that increases with Ga-68-DOTATATE uptake and decreases with F-18-FDG uptake. The variation in the FDZ score with respect to pathologic variables was examined. Kaplan-Meier and Cox regression analyses were performed to evaluate the effect of FDZ score on overall survival. An external cohort of 21 patients was used for validation. Results: The FDZ score was significantly higher in G3 NETs compared to G3 NECs (p<0.001), and was inversely correlated with Ki67 index ( R-2=0.33, p<0.001). Patients in the FDZ>0.05 group showed significantly longer survival compared to those in the FDZ <= 0.05 group, with median of 34.9 vs. 12.0 months (p<0.001). On univariate regression, FDZ>0.05 (p=0.005), well differentiated disease (p=0.044), and lower Ki67 index (p=0.042) were predictors of survival. On multivariate regression, only FDZ>0.05 could independently predict longer survival with HR=0.16 (p=0.018), which was reproduced in the external validation cohort. Conclusion: Combined quantification of F-18-FDG and Ga-68-DOTATATE PET/CT into a novel parameter, the FDZ score, reflects the pathologic characteristics of G3 GEP-NENs and is a prognostic indicator of overall survival independent of differentiation.