Pelvic Regional Control With 25 Gy in 5 Fractions in Stereotactic Radiation Therapy for High-Risk Prostate Cancer: Pooled Prospective Outcomes From the SHARP Consortium.

Purpose: To evaluate the efficacy of 25 Gy in 5 fractions (25 Gy/5#) prophylactic pelvic nodal irradiation for regional control during stereotactic radiation therapy (SBRT) for high-risk prostate cancer.

Methods And Materials: The multinational SHARP consortium database of patients treated with curative-intent prostate SBRT for high-risk prostate cancer was queried for prophylactic radiation therapy 25 Gy/5# to the pelvic lymph nodes. Details of Phoenix-defined biochemical failure and location of recurrence (local, regional, or distant) were extracted. Five-year biochemical failure-free survival (BFFS), metastasis-free survival, and overall survival were estimated by Kaplan-Meier method. Impact of potential prognostic factors (tumor stage, grade group [GG], prostate radiation therapy dose, and Androgen Deprivation Therapy (ADT) duration) was analyzed using Cox proportional hazards model.

Results: A total of 171 patients were eligible for analysis. Two-thirds of the patients had GG 4-5 cancer. Prostate was irradiated to 40 Gy/5# in 51.5% of the cohort, whereas the rest received 35 to 36.25 Gy/5#. Median ADT duration was 15 months (IQR, 9-24). Over a median follow-up of 51 months, biochemical failure was recorded for 19 (11.1%) patients. Restaging with Prostate Specific Membrane Antigen (PSMA)-Positron Emission Tomography Computed Tomography (PETCT) showed recurrence within the pelvic nodes in 3 patients, all with co-occurring distant metastases. Overall pelvic control was 98.2%, with 5-year BFFS and overall survival being 86.1% and 89.3%, respectively. None of the prognostic factors showed a statistically significant impact on BFFS, except GG (adjusted HR 3.6 [95% CI, 0.9-13.0], P = .06).

Conclusions: For high-risk prostate cancer treated with SBRT, prophylactic pelvic nodal irradiation with 25 Gy/5# achieved near universal regional control.