Dosimetry of lutetium-177 PSMA-targeted radiopharmaceutical therapies for prostate cancer patients: A comparative systematic review and meta-analysis.

e17033 Background: Novel theranostic approaches using radiopharmaceuticals targeting PSMA have emerged for treating metastatic castrate resistant prostate cancer (mCRPC). The physical properties and commercial availability of Lutetium-177 (Lu177) makes it one of the most used radionuclides for radiopharmaceutical therapy (RPT). In this review we aimed at comparing the dosimetry of the most used Lu177-PSMA RPT compounds. Methods: This is a systematic review and meta-analysis of Lu177-PSMA RPT (617, I&T, and J591) dosimetry for prostate cancer. Absorbed doses in Gy/GBq for each organ (kidney, parotid and submandibular glands, bone marrow, liver, lacrimal glands) and for tumor lesions (bone and non- bone lesions) were extracted. These were used to estimate the pooled average absorbed dose of each RPT, and normalize each to the respective injected activity (Gy/cycle) as determined by the dose per cycles used in VISION (7.4 GBq), SPLASH (6.8 GBq), and PROSTACT Trials (5.8 GBq). Results: 29 published manuscripts comprising 535 patients were included in the meta-analysis. The pooled dose was calculated for kidney based on (28 studies, 485 patients), parotid (20, 309), submandibular (7, 100) and lacrimal glands (9, 174), bone marrow (18, 293), and liver (14, 245) were 4.04 and 4.70, 5.85 and 2.62, 5.15 and 4.35, 11.03 and 19.23, 0.24 and 0.19 and 1.11 and 0.56 Gy respectively for Lu177-PSMA-617 and Lu177-PSMA-I&T. Lu177-PSMA-J591 reported absorbed doses to the kidney, bone marrow and liver were 3.95, 0.90, and 5.88 Gy respectively. There was no significant difference between Lu177-PSMA-I&T and Lu177-PSMA-617 for the dose to kidneys (p=0.10), submandibular glands (p=0.56), bone marrow (p=0.31), lacrimal glands (p=0.20), or tumors (p=0.16). However, parotid dose from Lu177-PSMA-617 was higher than that of Lu177-PSMA-I&T (p=<0.01). Average tumor doses tended to be higher for Lu177-PSMA-617 than for Lu177-PSMA-I&T, (27.94 vs. 21.31 Gy); p=0.16. Lu177-PSMA-J591 exposed the bone marrow and liver, to a significantly higher dose while resulting in a lower dose to the kidney than either of the two small molecule compounds. Absorbed doses to the salivary glands, lacrimal glands, and tumors after the treatment with Lu177-PSMA-J591 have not been published yet. Conclusions: The clinical impact of higher tumor to kidney dose ratio for Lu177-PSMA-617 than Lu177-PSMA-I&T has yet to be determined. Data for Lu177-PSMA-J591 are thus far too limited to draw firm conclusions.