1419P Radiobiological parameters for the assessment of 177Lu-PSMA-617 radioligand therapy in patients with metastatic castration-resistant prostate cancer

The lack of robust radiobiological data hampers the further optimization emerging 177Lu-PSMA-directed radioligand therapy (RLT). This study aims to explore several conventional parameters in assessment outcomes tumor and normal organs at risk (OARs) for castration-resistant prostate cancer (CRPC) patients. 20 patients received a median 3 (range 1–6, totally 86 cycles) 177Lu-PSMA-617 RLT were retrospectively included. Hematological status, renal liver function, serum PSA test before within two weeks post-therapy documented. Pre-therapy PSMA-PET/CT image dates collected establish CT-based organ segmentation. dosimetry each patient was measured using least 3-time-points SPECT/CT imaging. used determine response, related adverse events Dose including such as absorbed dose, integral dose (D10/50/90), biologically effective doses (BED) cumulated BEDs (cBED) tested. All are well-tolerated 19/20 partial response post-therapy. evaluation demonstrated high tumors compared OARs (p<.0001). Dosemean/max/sum target decreases treatment cycle increases. non-tumor-bearing bones is significantly correlated with hematological AEs (G2-4) (p<.05). larger PET-based volumes present higher (also when normalized administered activity). highest D10/50/90 by tumor-bearing bone, whole-body lymph/visceral regions respectively OARs. BED1.5 (AUROC: 0.633) cBED1.5 0.714) aggregable diagnostic accuracy detecting better post-treatment outcomes. Despite limited number this study, preliminary results encourage exploration models PSMA-RLT. In-depth analysis interpretation these still ongoing.