ESTRO 2024 - Abstract Book

S2519

Clinical - Urology

ESTRO 2024

ADT, and 5/25 pts received SRT, SBRT and ADT. Exclusive MDT approaches included: salvage pelvic lymph node dissection (s-PLND)in 3 cases and SBRT in 6 pts. In one case, ADT was combined with whole-brain RT. In 7/32 pts, the uptake was detected exclusively within the P-bed, and SRT was delivered (with ADT in 4/7 cases). Overall, the median bPFS for PSMA-positive pts was 11.9 months. 23/32 pts relapsed after a median interval of 10.4 months. Among the six pts receiving SBRT alone, 1/6 is currently in biochemical-control (52 months ADT-free). 5/6 recurred after a median interval of 10.4 months: 2/6 treated with a second-round of SBRT (1/2 with ADT), 2/6 observed, 1/6 treated with SRT+ADT. PSMA-PET was negative in 76/108 pts (70.3%) of whom 82.9% (63 patients) received SRT (3/63 with ADT). Among the remaining 13 patients, one died due to non-oncological causes, and 12 were further observed. Median bPFS for PSMA-negative pts undergoing SRT (n=63) was 35.7 months. Overall, a statistically significant difference (p<0.001) in terms of bPFS (Fig.1) was observed between PSMA-negative pts treated with SRT and PSMA-positive pts receiving tailored treatments. 20/63 pts treated with SRT experienced a recurrence after a median interval of 6.9 months. For this cluster of pts (20/63), patterns of failure were evaluated with either a second PSMA-PET (10/20 patients, with 6/10 exams resulting positive) and/or other imaging (10/20, with 8/10 resulting positive). Among the 14/20 positive exams, the sites of failure were as follows: 2 patients recurred within the P-bed, 4 had regional nodal recurrences, 2 patients had distant nodal recurrences, 3 patients had bone mets, and 3 patients had a recurrence in multiple sites.

Figure 1. bPFS, PSMA-negative vs PSMA-positive pts.

Conclusion:

A high proportion of PSMA-positive pts had an actually delivered RT plan different from the standard/intended P bed SRT plan. PSMA-PET negativity at first BCR following RP strongly relates to better prognosis compared with the cluster of PSMA-positive pts. P-bed exclusive SRT (with no ADT nor elective nodal irradiation) appeared to achieve suboptimal bPFS rates. Exclusive SBRT can delay ADT-initiation, but should be evaluated carefully. The optimal approach in this oncologic scenario remains to be fully defined [1,2]. Along with modern molecular imaging, genetic predictors are set to recover a major role in treatment guidance.

Keywords: Prostate Cancer, PSMA, SBRT