Utility of whole-body 68GA-PSMA-11 PET/CT parameters in predicting response to 177Lu-PSMA-617 radioligand therapy in chemotherapy and castration-resistant prostate cancer: A single center, retrospective study

Objective: The aim of the study was to investigate the predictive value of 68Ga-PSMA-11 PET/CT in patients with chemotherapy and castration resistant prostate cancer who underwent 177Lu-PSMA-617 radioligand therapy, concerning molecular response or progression. Materials and Methods: 48 patients who underwent 177Lu-PSMA-617 radioligand therapy between April 2019 and August 2023, were retrospectively analyzed. Demographic, clinical, and laboratory data, along with pre- and post-treatment 68Ga-PSMA-11 PET/CT images, were evaluated for associations, concerning molecular response and progression. Whole-body segmentation on pre-treatment PET/CT images were performed via METAVOL software. Parameters assessing total tumor burden and location-weighted metastatic burden were measured, with predictive values analyzed using SPSS 22.0, setting the significance level at p<0.05. Results: Among 48 patients, 58.3% of patients (n=28) were responsive while 41.7% (n=20) were not, and 29.2% (n=14) showed progression, while 70.8% demonstrated non-progression. Prostate cancer diagnosis duration over 12 months (OR=0.235, p=0.049), parotid SUVmax (OR=1.099, p=0.047) and SUVmean (OR= 1.137, p= 0.047) values, and the highest miM1 stage (OR=0,241, p=0,046) were found to be associated with molecular response. Molecular progression was significantly associated with the presence of lymph node metastasis (OR=0.144, p=0.006), bone-only metastasis (OR=4.333, p=0.030), ln/metTL-PSMA ratio (OR= .070, p=0.042), b/metTL-PSMA ratio (OR=13.085, p=0.040), and the distribution of bone/lymph node metastasis favoring lymph nodes according to TL-PSMA parameter (OR=0.385, p=0.044). Conclusion: The study suggests the potential utility of evaluating characteristics of disease extension, distribution of PSMA expression, and location-weighted metastatic burden for predicting molecular response and progression. Keywords: 177Lu-PSMA, PET/CT, RECIP 1.0, PSMA-TV, TL-PSMA