(UroToday.com) The Society of Nuclear Medicine & Molecular Imaging (SNMMI) 2024 Annual Meeting held in Toronto, ON between June 8th and June 11th, 2024 was host to a prostate cancer imaging session. Dr. Isabel Rauscher presented the results of an analysis of 18F-rhPSMA-7 and 18F-flotufolastat PET-guided salvage radiotherapy in recurrent prostate cancer.
Traditionally, prostate cancer patients with biochemical recurrence following radical prostatectomy have received salvage radiotherapy to the prostate bed. However, PSMA-PET/CT is now approved in the biochemically recurrent setting owing to its improved performance characteristics that may alter treatment decision-making and, theoretically, improve oncologic outcomes. 18F-rhPSMA-7.3 (18F-flotufolastat) was recently approved by the United States Food and Drug Administration (FDA) and demonstrates lower urinary excretion compared to most other PSMA-PET ligands. In this study, the investigators compared disease outcomes of patients who underwent 18F-rhPSMA-7 or 18F-flotufolastat PET-guided salvage radiotherapy to those undergoing conventional salvage radiotherapy.
This was a retrospective study of 110 patients with biochemical recurrence following a radical prostatectomy, defined as PSA ≥0.2 ng/ml, who received image-guided intensity-modulated salvage radiotherapy to the prostate bed and/or pelvic lymphatics. Of these 110 patients, 28 underwent conventional salvage radiotherapy without PET guidance. The remaining 82 patients received 18F-rhPSMA-7 or 18F-flotufolastat PET-guided salvage radiotherapy with dose escalation to PET avid lesions. The primary study endpoint was biochemical failure-free survival at 48 months post-salvage radiotherapy, defined as PSA nadir + 0.2 ng/ml. The median patient follow-up was 22.6 months.
Among the 82 patients undergoing PET/CT, the following disease spread patterns were observed:
- Local recurrence only: 61/82 (74%)
- Lymph node metastases only: 12/82 (15%)
- Local recurrence and lymph node metastases: 9/82 ( 11%)
Salvage radiotherapy was directed as follows:
- Prostate bed alone: 52/82 (63%)
- Pelvic lymphatics alone: 5/82 (6.1%)
- Both prostate bed and pelvic lymphatics: 25/82 (30%)
In the conventional salvage radiotherapy group, 25/28 (89%) received salvage radiotherapy to the prostate bed only, and 3/28 (11%) received salvage radiotherapy to both the prostate bed and pelvic lymphatics.
Overall, biochemical failure-free survival was non-significantly longer in the PET-guided salvage radiotherapy group (p=0.101):
- PET-guided group: Median not reached
- Conventional salvage radiotherapy group: 45.6 months (95% CI: 27.5–63.7)
The 12, 24, and 36 months biochemical-failure free survival rates for the PET-guided and conventional salvage radiotherapy groups were as follows:
- 12 months: 95% versus 87%
- 24 months: 90% versus 75%
- 36 months: 89% versus 68%
When analysis was limited to patients receiving salvage radiotherapy to the prostate bed only, biochemical failure-free survival was similarly longer in the PET-guided salvage group (median: not reached versus 55.1 months, p=0.063).
The study investigators concluded that 18F-rhPSMA-7 or 18F-flotufolastat PET-guided salvage radiotherapy results in more favorable disease outcomes than conventional salvage radiotherapy without PET guidance, although statistical significance was not reached most likely due to the limited sample size. However, these data illustrate the potential of 18F-flotufolastat-guided salvage radiotherapy for a personalized radiotherapeutic management approach.
Presented by: Isabel Rauscher, MD, Senior Physician, Clinic for Nuclear Medicine at Klinikum Rechts der Isar, Technical University of Munich, Germany
Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting, Chicago, IL, Fri, May 31 – Tues, June 4, 2024.