ESTRO 2024 - Abstract Book

S2384

Clinical - Urology

ESTRO 2024

specific membrane antigen-positron emission tomography (PSMA-PET) has emerged as the most powerful tool to guide treatment of the macroscopic disease (local recurrence or pelvic lymph nodes) with higher doses. In recent years, radiohybrid PSMA-(rhPSMA)-ligands have been developed as truly theranostic agents. 18 F-rhPSMA-7 and its single isomer derivate 18 F-rhPSMA-7.3 are high-affinity PSMA-targeting radiopharmaceuticals for PET imaging. 18 F rhPSMA-7.3 has been recently approved by the FDA under the drug name 18 F-flotufolastat and has been included in the updated NCCN guidelines. Clinical data show 18 F-flotufolastat to have lower average urinary excretion than values reported for most other PSMA-PET radiopharmaceuticals potentially improving imaging in the pelvis.

We aimed to explore disease outcomes from patients who underwent 18 F-flotufolastat and 18 F-rhPSMA-7 PET-guided SRT compared with those undergoing conventional SRT (C-SRT) without PET.

Material/Methods:

We retrospectively evaluated biochemical failure-free survival (bFS; PSA nadir + 0.2 ng/mL and one confirmation value) and overall rates of bFS at time points up to 48 months post-SRT. We included 110 evaluable patients with BCR (PSA ≥0.2 ng/mL) after RP who received image -guided intensity-modulated SRT to the prostate bed and/or pelvic lymphatics. Patients had a median age of 72.0 years (range 50.0-84.0 years) and were followed up for a median 22.6 months (range 1.0 – 139.0 months). Patients were treated with PET-guided SRT with dose escalation to PET-avid locations (n=82) or with C-SRT without PET guidance and dose escalation (n=28).

Results:

In patients who received PET imaging, local recurrence only, lymph node metastases only, and both local recurrence and lymph node metastases were present in 61/82 (74%), 12/82 (15%), and 9/82 (11%) patients, respectively.

In the PSMA PET-guided group, SRT to the prostate bed alone, pelvic lymphatics alone, and both prostate bed and pelvic lymphatics were performed in 52/82 (63%), 5/82 (6%), and 25/82 (31%) patients, respectively. In the C-SRT group, 25/28 (89%) received SRT to the prostate bed alone, and 3/28 (11%) received SRT to the prostate bed and pelvic lymphatics. Overall bFS was longer with PSMA PET-guided SRT than C-SRT (p=0.101), although statistical significance was not reached. The median bFS was 45.6 months (95%-CI: 27.5 – 63.7 months) in the C-RT group and was not reached in the PSMA PET-guided SRT cohort. The %bFS was 95% (52/55) vs. 87% (20/23), 90% (27/30) vs. 75% (15/20), 89% (16/18) vs. 68% (13/19) and 100% (3/3) vs. 57% (8/14) for PSMA PET-guided SRT vs. C-SRT at 12, 24, 36, and 48 months, respectively. For the subgroup of patients with treatment of the prostate bed only, a clear trend towards a longer bFS was noted for PSMA PET-guided SRT (n=52) compared with C-SRT (n=25; p=0.063). The median bFS in the C-SRT cohort was 55.1 months (95%-CI: 40.9 – 69.3 months) and was not reached in the PSMA PET-guided SRT cohort. The %bFS was 97% (31/32) vs. 85% (17/20), 95% (20/21) vs. 82% (14/17), 92% (11/12) vs. 75% (12/16) and 100% (2/2) vs. 67% (8/12) at 12, 24, 36, and 48 months, respectively.

Conclusion: