18F-rhPSMA-7 Versus Conventional Salvage Radiotherapy for BCR

New research presented at the 2024 Society of Nuclear Medicine and Molecular Imaging Annual Meeting provides evidence of ¹⁸F-rhPSMA-7 or ¹⁸F-flotufolastat positron emission tomography (PET)-guided salvage radiotherapy (SRT) leading to more favorable disease outcomes than conventional SRT (C-SRT) for patients with biochemical recurrence (BCR) of prostate cancer after radical prostatectomy (RP).

Patients with BCR after RP have traditionally received SRT. However, prostate-specific membrane antigen (PSMA) PET has evolved as a resource to guide treatment and may lead to improved patient outcomes. One such PSMA PET imaging product, ¹⁸F-rhPSMA-7.3, was recently approved by the US Food and Drug Administration with lower urinary excretion than most other PSMA PET ligands.

Isabel Rauscher, MD, of the Technical University of Munich (Germany), and colleagues designed a study to explore disease outcomes of patients who underwent ¹⁸F-rhPSMA-7 or ¹⁸F-flotufolastat PET-guided SRT compared with those undergoing C-SRT. The retrospective analysis included 110 patients with BCR (prostate-specific antigen [PSA] ≥0.2 ng/mL) after RP who received image-guided intensity-modulated SRT to the prostate bed and/or pelvic lymphatics.

Patients were treated with ¹⁸F-rhPSMA-7 or ¹⁸F-flotufolastat PET-guided SRT with dose escalation to PET-avid locations (n=82) or with C-SRT without PET guidance and dose escalation (n=28). Researchers evaluated biochemical failure-free survival (bFFS)—where biochemical failure is defined as PSA nadir +0.2 ng/mL—and overall rates of bFFS at time points up to 48 months post-SRT.

Patients were followed up for a median of 22.6 months. Dr. Rauscher and colleagues found that in patients receiving PET-guided imaging, local recurrence only, lymph node metastases (LNM) only, and both local recurrence and LNM were present in 74%, 15%, and 11%, respectively.

SRT to the prostate bed alone, pelvic lymphatics alone, and both the prostate bed and pelvic lymphatics was performed in 63.0%, 6.1%, and 30.0% of these patients, respectively. In the C-SRT group, 89.3% received SRT to the prostate bed alone, and 10.7% received SRT to the prostate bed and pelvic lymphatics.

Researchers reported that overall bFFS was longer with ¹⁸F-rhPSMA-7 or ¹⁸F-flotufolastat PET-guided SRT compared with C-SRT (not reached vs 45.6 months, respectively), though they noted that this was not statistically significant (P=.101). For ¹⁸F-rhPSMA-7 or ¹⁸F-flotufolastat PET-guided SRT versus C-SRT at 12, 24, 36, and 48 months, the bFFS was 95% versus 87%, 90% versus 75%, 89% versus 68%, and 100% versus 57%, respectively.

Furthermore, they added that among patients treated in the prostate bed only, a longer bFFS was noted for ¹⁸F-rhPSMA-7 or ¹⁸F-flotufolastat PET-guided SRT (n=52; median bFFS not reached) compared with C-SRT (n=25; median bFFS, 55.1 months; P=.063).

“These data illustrate the potential of ¹⁸F-flotufolastat-guided SRT to be considered as part of personalized radiotherapeutic management,” Dr. Rauscher and colleagues concluded.