Prostate Cancer Recurrence: Examining the Role of Salvage Radiotherapy Field and Risk Factors for Regional Disease Recurrence Captured on 18F-DCFPyL PET/CT

Abstract

PurposeThe role of elective pelvic nodal irradiation in salvage radiotherapy (sRT) remains controversial. Utilizing 18F-DCFPyL PET/CT, this study aimed to investigate differences in disease distribution after whole pelvic (WPRT) or prostate bed (PBRT) radiotherapy and to identify risk factors for pelvic lymph node (LN) relapse. MethodsThis retrospective study included patients who underwent 18F-DCFPyL PET/CT with a PSA > 0.1 ng/mL after either radical prostatectomy (RP) or RP and sRT. Disease distribution on 18F-DCFPyL PET/CT in patients after salvage PBRT and WPRT was compared using Chi-square tests for independence. Risk factors were tested for association with pelvic LN relapse after RP and after salvage PBRT using logistic regression. Results979 18F-DCFPyL PET/CTs performed at our institution between 1/1/2022 – 3/24/2023 were analyzed. There were 246 patients meeting criteria, of which 84 received salvage RT after RP (post-salvage RT group) and 162 received only RP (post-RP group). Salvage PBRT patients (n = 58) had frequent pelvic nodal (53.6%) and nodal-only (42.6%) relapse. Salvage WPRT patients (n = 26) had comparatively lower rates of pelvic nodal (16.7%, p = 0.002) and nodal-only (19.2%, p = 0.04) relapse. The proportion of distant metastases in the salvage PBRT (34.5%) and WPRT (46.2%) groups did not differ (p = 0.309). Multiple patient characteristics were associated with pelvic LN disease in the post-RP group, including ISUP grade (Odds Ratio 2.01, p = 0.001) and seminal vesicle invasion (OR 3.85, p = 0.021). ConclusionAt PSA persistence or progression, salvage WPRT in this cohort resulted in lower rates of nodal involvement than salvage PBRT, but did not reduce distant metastases. Certain risk factors increase the likelihood of pelvic LN relapse after RP and can help inform salvage RT field selection. MicroAbstractOptimal patient selection for salvage whole pelvic radiotherapy (WPRT) remains uncertain. This study utilized 18F-DCFPyL PET/CT, a novel and highly sensitive imaging modality, to compare disease distribution after prostate bed (PBRT) or WPRT. PBRT resulted in higher rates of pelvic nodal and nodal-only recurrences, indicating that WPRT may benefit patients at higher risk for lymph node disease.