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IntroductionTens of different Prostate Specific Membrane Antigen (PSMA) targeting radiopharmaceuticals for both imaging and therapy have been synthesized. Although variability in biodistribution and affinity for binding to the PSMA receptor between different PSMA targeting radiopharmaceuticals are known, little is known about the clinical implications of those variabilities. Therefore, in this study differences in interreader agreement and detection rate between two regularly used 18 F-labeled PSMA-receptor targeting radiopharmaceuticals [ 18 F]-DCFPyL and [ 18 F]-PSMA-1007 were analyzed. Material and methods One hundred and twenty consecutive patients scanned with [ 18 F]-PSMA-1007 were match-paired with 120 patients scanned with [ 18 F]-DCFPyL. All 240 PET/CTs were reviewed by two readers and scored according to PSMA-RADS reading criteria for PSMA PET/CT. Inter-reader agreement and detection rate of suspected lesions were scored for different anatomical locations including prostate/prostatic fossa, lymph nodes, bone, and other locations. ResultsLarge equality between [ 18 F]-DCFPyL and [ 18 F]-PSMA-1007 was found; however, some clinically relevant and statistically significant differences were observed. [ 18 F]-PSMA-1007 detected suspected prostatic/prostatic fossa lesions in a higher proportion of patients and especially in the subcohort of patients scanned for biochemical recurrence. [ 18 F]-DCFPyL and [ 18 F]-PSMA-1007 showed equal ability for detection of suspected lymph nodes, although inter-reader agreement for [ 18 F]-DCFPyL was higher. [ 18 F]-DCFPyL showed less equivocal skeletal lesions and higher inter-reader agreement for skeletal lesions.The majority of equivocal lesions found with PSMA-1007 (at least were determined to be aof nonmetastatic origin. ConclusionClinically relevant differences, which may account for diagnostic dilemmas, were observed between of [ 18 F]-DCFPyL and [ 18 F]-PSMA-1007. Those findings encourage further studies, as they may have consequences for selection of the proper PSMA targeting radiopharmaceutical.

Background 18 F-fluorocholine (FCH) PET/CT is a promising technique for visualizing hyperfunctioning parathyroid glands in hyperparathyroidism. It is still under debate whether to use this technique as a first-line imaging modality or to use it when conventional techniques such as 99m Tc-sestamibi scintigraphy or ultrasonography are inconclusive. This study evaluates FCH PET/CT as a first-line modality. Methods Patients with primary hyperparathyroidism, referred between June 2015 and December 2018 for FCH PET/CT as a first-line imaging method, were included in this study. Baseline characteristics, clinical data, scan results, and type of treatment were recorded. The rate of correct detection was calculated on a per patient-based and a per lesion-based analysis. The reference standard comprised histopathological results, intraoperative response to parathyroidectomy, and clinical follow-up. Results Two hundred and seventy-one patients were included, of which 139 patients underwent parathyroidectomy, 48 were treated with calcimimetics, and 84 patients received further follow-up without active treatment. In the surgically treated group, a single adenoma was suspected in 127 scans, double adenoma in three scans, and one scan showed evidence of three hyperfunctioning glands. In eight scans, no lesions were visualized. A total of 154 parathyroid glands were surgically removed. The rate of correct detection was calculated at 96% and 90%, on a per patient-based and per lesion-based analysis, respectively. Conclusion This retrospective study in a large cohort shows high detection rates of FCH PET/CT in primary hyperparathyroidism, which is in accordance to literature. The use of FCH PET/CT as a first-line imaging modality in preoperative planning of parathyroid surgery may therefore be a suitable choice.

18 F-fluorocholine ( 18 F-FCH) PET/CT is a promising and increasingly used scan technique in the preoperative imaging of parathyroid adenoma. Several acquisition methods have been evaluated in the literature, but the optimal image acquisition time point after administration of the tracer is still under debate. Methods: Patients who had hyperparathyroidism, underwent dual-time-point 18 F-FCH PET/ CT (image acquisition, 5 min; 60 min after injection), and had histologically proven pathologic parathyroid glands were retrospectively included in the study. Early and late images were compared both visually and quantitatively. Results: Sixty-four patients were included, and a total of 71 parathyroid glands were surgically removed. Visually, there were no differences between early and late images of hyperfunctioning parathyroid glands in 44 patients (69%); in 13 patients (20%), visualization on early images was better; in 6 patients (9%), visualization of hyperfunctioning glands was best on late images; and in 1 patient (2%), the lesion was exclusively visualized on late images. For the total cohort, there was a significant decrease in 18 F-FCH uptake in the glands on late versus early time points (P 5 0.001), but there was a significant increase in the ratio of parathyroid uptake to thyroid uptake (P 5 0.037). The group of patients with better visualization on early images showed a decrease over time in both parathyroid uptake and the ratio of parathyroid uptake to thyroid uptake, significant in comparison to those in both the group with better visualization at later time points and the group in which visualization was similar at both time points (P values of 0.000-0.018). There were no significant differences in 18 F-FCH uptake and the ratio of parathyroid uptake to thyroid uptake between the latter 2 groups (P values of 0.200-0.709). Conclusion: In most patients (89%), hyperfunctioning parathyroid glands were adequately visualized on early imaging; however, in a subset of patients (11%), such glands were best visualized at later time points. Therefore, we recommend the acquisition of dual-time-point images in parathyroid imaging with 18 F-FCH PET/CT or the creation of an opportunity to acquire additional late images after review of early images when findings are inconclusive.

Radioisotope-labeled prostate-specific membrane antigen PET/CT is increasingly used for detection of prostate cancer most often in the setting of biochemical recurrence or in primary staging. This report shows increased PSMA expression in lymph node metastases 3 months after initiation of enzalutamide for castration-resistant prostate cancer, whereas lymph node volume and serum prostate-specific antigen decreases over time. This case demonstrates that increasing 18F-DCFPyL uptake after initiation of androgen deprivation therapy should not be confused with disease progression.