Biochemical Relapse-Free Survival in Postprostatectomy Patients Receiving 18F-Fluciclovine-Guided Prostate Bed-Only Radiation: Post Hoc Analysis of a Prospective Randomized Trial

Abstract

PurposeWhole pelvis (WP) radiation therapy (radiation) improved biochemical relapse free survival (bRFS) compared to prostate-bed (PB)-only radiation in RTOG 0534 but was performed in an era prior to PET staging. Separately, 18F-fluciclovine PET/CT (PET)-guided post-prostatectomy radiation improved 3-year bRFS versus radiation guided by conventional imaging alone. We hypothesized that patients who were changed from WP to PB-only radiation after PET would have bRFS3 that was (a) no higher than patients initially planned for PB-only radiation & (b) lower than patients planned for WP radiation without PET guidance. Methods and MaterialsWe conducted a post-hoc analysis of a prospective, randomized, trial comparing conventional (Arm 1) v. PET-guided (Arm 2) post-prostatectomy radiation. In Arm 2, pre-PET treatment field decisions were recorded & post-PET fields were defined per protocol: pathologic node negative (pN0) without pelvic or extrapelvic PET uptake received PB-only radiation. Three-year bRFS was compared in patients planned for WP with change to PB-only radiation [Arm 2 (WP:PB)] v Arm 2 patients planned for PB-only with final radiation to PB-only [Arm 2(PB:PB)] & Arm 1 pN0 patients treated with WP radiation [Arm 1(WP)] using Z test and log-rank test. Demographics were compared using Chi-square test, Fisher's exact test, or ANOVA as appropriate. ResultsWe identified 10 Arm 2(WP:PB), 31 Arm 2(PB:PB) and 11 Arm 1(WP) patients. Androgen deprivation was used in 50.0% of Arm 2(WP:PB) & 3.2% of Arm 2(PB:PB) patients, p<0.01. Median pre-radiation PSA was higher in Arm 2(WP:PB) vs Arm 2(PB:PB) patients (0.4 v 0.2 ng/mL, p=0.03), however, there were no significant differences in T-stage, Gleason score, or margin positivity. Three-year bRFS was 80% in Arm 2(WP:PB) vs 87.4% in Arm 2(PB:PB), p=0.47, respectively. Arm 1(WP) patients had significantly worse three-year (23%) bRFS vs Arm 2(WP:PB), p<0.01. ConclusionsPatients initially planned for WP radiation with field decision change to PB-only radiation after PET showed (a) no significant difference in 3-year bRFS compared to patients initially planned for PB-only radiation and (b) improved bRFS compared with patients receiving WP radiation without PET guidance. PET-guided volume de-escalation in selected patients may be one approach to mitigating toxicity without compromising outcomes.