Abstract Introduction Semi-quantitative uptake measurements are part of the PROMISE framework for PET/CT interpretation of tracers targeting the prostate-specific membrane antigen (PSMA), where tumor uptake is compared to uptake in reference tissues. 18FPSMA-1007 has primarily hepatobiliary excretion and it is suggested to use spleen as reference tissue instead of liver. The aim of this study is to investigate the normal range and interpatient variability of 18FPSMA-1007 uptake in reference tissue for prostate cancer patients, with particular focus on the splenic uptake. Materials and methods A total of 102 18FPSMA-1007 PET/CT scans of prostate cancer patients with biochemical recurrence (BCR) from three hospitals were included in the analysis. SUV max and SUV mean measurements were performed in the blood pool, liver, spleen, and parotid glands. Results are reported as median with percentiles 5th, 95th. Results For 15/102 (15%) and 20/102 (20%) of the patients, the SUV max and SUV mean , respectively, were higher in the spleen than in the parotid glands. Median SUV max of the reference tissues were 1.2 0.6, 2.2 for blood, 15.8 8.9, 26.2 for spleen, and 26.6 14.5, 40.4 for the parotid glands. Median SUV mean were 11.9 6.6, 20.7 for spleen and 19.3 11.2, 32.1 for the parotid glands. Conclusion In this multicenter cohort of BCR patients, 18FPSMA-1007 reference tissue uptake is reported in accordance with the PROMISE protocol. A substantial number of patients present with higher uptake in the spleen than in parotid glands, for reasons that are currently unexplained. Care should be taken when interpreting these values until further studies are conducted. Key Points Question The normal range for 18FPSMA-1007 uptake values in PROMISE reference tissues are not well documented, challenging standardized lesion categorization in prostate cancer PET interpretation . Findings In a multicenter cohort, splenic 18FPSMA-1007 uptake exceeded parotid gland uptake in a notable subgroup (15%), leading to situations where PSMA expression scoring according to the PROMISE framework cannot be applied as intended . Clinical relevance Unexpectedly high splenic uptake relative to parotid gland uptake of 18FPSMA-1007 in some patients may affect lesion categorization; careful interpretation is advised . Graphical Abstract
Abrahamsen et al. (Thu,) studied this question.