Salvage Involved-Field and Extended-Field Radiation Therapy in Positron Emission Tomography–Positive Nodal Recurrent Prostate Cancer: Outcomes and Patterns of Failure

PURPOSE: The optimal salvage pelvic treatment for nodal recurrences in prostate cancer is not yet clearly defined. We aimed to compare outcomes of salvage involved-field radiation therapy (s-IFRT) and salvage extended-field radiation therapy (s-EFRT) for positron emission tomography/computed tomography–positive nodal-recurrent prostate cancer and to analyze patterns of progressions after salvage nodal radiation therapy. METHODS AND MATERIALS: Patients with (18)F-fluorocholine or (68)Ga prostate-specific membrane antigen ligand positron emission tomography/computed tomography–positive nodal-recurrent prostate cancer and treated with s-IFRT or s-EFRT were retrospectively selected. Time to biochemical failure, time to palliative androgen deprivation therapy (ADT), and distant metastasis–free survival were analyzed. RESULTS: Between 2009 and 2019, 86 patients were treated with salvage nodal radiation therapy: 38 with s-IFRT and 48 with s-EFRT. After a median follow-up of 41.9 months (5.4-122.1 months), 47 patients presented a further relapse: 31 after s-IFRT and 16 after s-EFRT, with only 1 in-field relapse. The median time to palliative ADT was 24.8 months (95% confidence interval [CI], 13.3-93.5 months) in the s-IFRT group and not yet reached (95% CI, 40.3 months to not yet reached) in the s-EFRT group (P = .010). The 3-year biochemical failure–free rate was 70.2% (95% CI, 51.5%-82.9%) with s-IFRT and 73.9% (95% CI, 55.4%-85.7%) with s-EFRT (P = .657). The 3-year distant metastasis–free survival was 74.1% (95% CI, 56.0%-85.7%) with s-IFRT and 82.0% (95% CI, 63.0%-91.8%) with s-EFRT (P = .338). CONCLUSIONS: s-EFRT and s-IFRT for positron emission tomography–positive nodal-recurrent prostate cancer provide excellent local control. Time to palliative ADT was longer following s-EFRT than following s-IFRT.