Clinical Impact of PSMA PET Fusion-Based RT Planning on Dosimetry and PSA Response in Prostate Cancer

Background: This study aimed to assess the impact of PSMA-PET/CT fusion imaging on target volume delineation in prostate cancer RT and to evaluate its effects on dosimetric parameters and PSA response, including intraprostatic boost. Methods: This single-center, retrospective study included 138 prostate cancer patients treated with definitive RT. Patients were evaluated according to the use of PSMA-PET/CT fusion-based planning and an intraprostatic focal boost, and dosimetric parameters for target volumes and organs at risk were compared. Results: PSMA-PET/CT fusion-based planning significantly increased the minimum dose coverage of the prostate target volume (96.7% vs. 95.5%, p = 0.003) while reducing the maximum dose (104.8% vs. 106.1%, p < 0.001). At 1 year after RT, the median change in PSA from baseline was 0.08 ng/mL (range, -0.44-2.12) in patients who underwent PSMA PET imaging-based fusion planning compared with 0.01 ng/mL (range, -0.049-4.07) in those who did not (p = 0.010). In patients receiving the intraprostatic focal boost with PSMA-PET/CT fusion, rectal maximum dose percentages were significantly lower than in those without the boost (103.2% [98.9-106.7] vs. 103.8% [95.7-107.4], p = 0.026). Rectal V65 and V50 values were also significantly reduced in the fusion group (7.0% [0.7-19.8] vs. 5.2% [1.2-21.7], p = 0.007; and 13.6% [6.3-21.9] vs. 11.4% [4.4-29.2], p = 0.027, respectively). Bladder maximum dose percentages were significantly lower in patients receiving the PSMA-PET/CT fusion-guided intraprostatic boost compared with those without the boost (102.6% [99.7-107.9] vs. 104.5% [99.1-108.5], p = 0.001). Conclusions: PSMA-PET/CT fusion-based planning improves biologically guided target delineation and dose homogeneity and suggests potential for better early biochemical response while reducing normal tissue exposure, whereas the intraprostatic focal boost improves dose distribution but is not associated with a significant short-term (1-year) PSA benefit.