Impact of Body Composition on Dosimetry of 177Lu-PSMA Radioligand Therapy

Prostate-specific membrane antigen (PSMA) is highly expressed in metastatic castration-resistant prostate cancer. 177Lu-PSMA-617 is a radioligand therapy delivering beta-particle radiation to PSMA-expressing cells. The VISION trial demonstrated significant improvement in progression-free and overall survival compared to standard of care. Hypotheses: patients with higher fat mass may have better treatment response due to higher tumor dose; discordance between BMI-based and CT-based body composition measurements; SUV quantification in PET/CT and SPECT/CT depends on patient morphology; dosimetry of organs at risk depends on morphology; body composition changes during treatment; PSA kinetics are modified by dosimetry. Study design: patients scheduled for 177Lu-PSMA treatment (4 or 6 cycles, 7400 MBq IV every 6 weeks) are enrolled. After cycle 1, SPECT/CT is performed at 72-96H (all patients) and additionally at 4-24H and 168-196H (40 patients for multipoint dosimetry). Body composition is extracted from the non-injected CT component of SPECT/CT using Anthropometer3DNet. Nutritional assessment (MNA questionnaire, blood tests including albumin, transthyretin, CRP, PSA) is performed at baseline (C1) and end of treatment (C4 or C6).