Prognostic value of quantitative PSMA-PET parameters during chemotherapy in prostate cancer.

33 Background: PSMA-PET/CT is increasingly being used to monitor chemotherapy in prostate cancer and shows promise for predicting outcomes and improving response evaluation. This retrospective study aimed to determine the prognostic value of quantitative tumor burden parameters derived from PSMA-PET/CT for overall survival (OS) during taxane-based chemotherapy. Methods: Databases from 6 institutions were screened for patients who underwent[ 68 Ga]Ga-PSMA11-PET and serum PSA measurements at baseline and within three months after last taxane based chemotherapy dose. Tumor segmentation was performed using DeepPSMA software and PSMA-PET whole-body quantitative parameters were obtained: PSMA-positive tumor volume (PSMA-VOL) and maximum/average standardized uptake value (SUV max , SUV mean ). Univariate Cox-regression analyses by hazard ratio (HR) with 95% confidence interval (CI) were used to evaluate association of whole-body quantitative PSMA parameters and PSA levels with OS. Harrell’s concordance index (C-index) was used to determine prognostic accuracy. Optimal cut points were determined by maximizing the log-rank statistic. Results: A total of 128 patients were included, of whom 62/128 (48%) had castration-sensitive prostate cancer and 66/128 (52%) castration-resistant prostate cancer. At baseline, PSMA-VOL numerically reached the highest prognostic value for OS (C-index: 0.88) followed by PSA (C-index: 0.80, p = 0.85), while the percentage change in PSA levels had the highest prognostic value during treatment (C-index: 0.94) significantly higher than percentage change in PSMA-VOL (C-index: 0.85, p = 0.02), (complete data shown in Table 1). Conclusions: Baseline and post-therapeutic PSMA-PET/CT quantitative parameters are prognostic for OS after taxane-based chemotherapy in prostate cancer. Baseline PSMA-VOL had the highest prognostic value for OS, while changes in PSA levels outperformed changes in quantitative PSMA-PET parameters during treatment. Parameter Cut point HR (95% CI) P-value C-index (95% CI) PSMA vol , baseline > 28 ml 5.59 (2.77 – 11.27) < 0.001 0.88 (0.81 – 0.96) SUV mean , baseline < 13.2 2.00 (0.96 – 4.15) 0.06 0.29 (0.13 – 0.45) SUV max , baseline > 71 2.18 (1.23 – 3.86) 0.007 0.69 (0.57 – 0.82) PSA, baseline > 3.9 ng/ml 3.53 (1.75 – 7.13) < 0.001 0.80 (0.69 – 0.92) PSMA vol , relative change > -21 % 4.48 (2.80 – 7.17) < 0.001 0.85 (0.78 – 0.91) SUV max , relative change > -70 % 2.42 (1.50 – 3.82) < 0.001 0.76 (0.67 – 0.86) SUV mean , relative change > -44 % 5.98 (2.57 – 13.88) < 0.001 0.85 (0.73 – 0.98) PSA, relative change > -97 % 7.03 (3.20 – 15.43) < 0.001 0.94 (0.88 – 0.99)