Salvage Interstitial Brachytherapy for Isolated Local Recurrence of Cervical and Endometrial Cancer: A Retrospective Analysis Stratified by Type of Pelvic Irradiation History

<b>Background/Objectives</b>: This study evaluated the efficacy and safety of salvage interstitial brachytherapy (S-ISBT) for isolated local recurrence (ILR) of cervical and endometrial carcinoma, stratifying patients by pelvic irradiation history (PIH). <b>Methods</b>: Patients with ILR treated with S-ISBT were retrospectively reviewed and categorized by initial treatment: Group A (surgery alone); Group B (surgery + postoperative radiotherapy (RT)); and Group C (definitive RT). Overall survival (OS), progression-free survival (PFS), local control (LC) rates, and the cumulative incidence functions (CIFs) for Grade ≥ 3 late adverse events (AEs) were estimated. Multivariate analysis identified prognostic factors. <b>Results</b>: The study included 70 patients (A: 28, B: 17, C: 25) with a median follow-up of 33.4 months. The 3-year OS, PFS, LC, and CIFs for Grade ≥ 3 late AEs for Groups A, B, and C were 80.8%, 66.7%, and 30.4% (<i>p</i> < 0.001); 56.4%, 41.5%, and 11.6% (<i>p</i> < 0.001); 89.1%, 61.4%, and 43.0% (<i>p</i> = 0.002); and 26.4%, 13.3%, and 32.0% (<i>p</i> = 0.40), respectively. Multivariate analysis suggested the type of PIH, disease-free interval, and tumor volume as independent prognostic factors. While no significant differences were observed between Groups A and B (OS: HR = 0.47, <i>p</i> = 0.19; PFS: HR = 0.60, <i>p</i> = 0.28), Group C exhibited a significantly higher risk than Group B (OS: HR = 3.08, <i>p</i> = 0.018; PFS: HR = 3.41, <i>p</i> = 0.004). <b>Conclusions</b>: S-ISBT could be considered for patients with prior postoperative RT, whose outcomes are significantly better than those with prior definitive RT.