CT-guided Adjuvant Vaginal Brachytherapy for Endometrial Cancer: Efficacy and Sites of Failure with a Low-Dose Regimen

Abstract

To evaluate clinical outcomes and sites of failure for women with early stage endometrial adenocarcinoma treated with adjuvant vaginal brachytherapy (VB) with a low dose scheme. Retrospective review identified 318 patients with FIGO stage I-II endometrioid endometrial cancer who received adjuvant VB to a dose of 24 Gy in 6 fractions from 2005-2017. Patients with less than 6 months (mo) follow-up were excluded (n=75). Dose was prescribed to cylinder surface and median activation length was 4.5 cm. Full vaginal length was treated for LVI. CT imaging was performed prior to each fraction to assess cylinder depth, diameter and vaginal length. Kaplan-Meier method was used to estimate rates of vaginal relapse (VR), pelvic nodal relapse (PNR), distant metastasis including para-aortic relapse (DM), recurrence-free survival (RFS) and overall survival (OS). Univariate analysis was performed by logrank test or Cox proportional hazards. Pre-treatment CT images were analyzed for patients with VR. Clinical characteristics of the 243 eligible patients are summarized in the Table. With median followup of 42 mo, 16 patients had recurrence at a median 21 mo after surgery. At 3 years, rates of VR, PNR, DM, RFS and OS were: 1.9%, 1.5%, 4.3%, 94.1% and 98.9%. By GOG-99 risk groups, 3-year RFS rates were 100%, 95.8% and 90% for low, low-intermediate (LIR) and high-intermediate risk (HIR) disease, respectively (p=0.19). Age, stage, BMI and LVI were not associated with RFS (all p>0.2). On pre-treatment CT images, 3 patients had distal VR at the introitus, which did not receive the prescription dose. Three patients recurred at the vaginal cuff or fornix. Patients with VR had higher BMI than those without VR (median 34 vs. 28, respectively, p=0.05). Cervical mucosal or stromal involvement was also associated with VR (3-year: 10% vs. 1% with none, p=0.06). Age, grade, LVI, and time to brachytherapy were not associated with VR (all p>0.2). The 3-year VR rates by GOG-99 risk groups were 0%, 1.4% and 3.2% for low, LIR, and HIR disease (p=0.5). By PORTEC, 3-year VR rate was 1.3% for HIR disease. Adjuvant vaginal brachytherapy with a low dose regimen results in excellent clinical outcomes for patients with early stage endometrial cancer. Patients with higher BMI and cervical extension may be at increased risk of VR, and additional study is needed to determine optimal brachytherapy treatment parameters.Abstract TU_19_3504: Table 1Age (median)63.1 years (range, 29.7 - 89.2)Body Mass Index (median)28,8 kg/m2 (range, 18.4 - 57.5)FIGO 2009 Stage IA IB II: 51% (124) 42% (103) 7% (16)GOG-99 Risk Group Low-Risk Low-intermediate risk (LIR) High-intermediate risk (HIR): 3% (7) 66% (161) 31% (75)PORTEC HIR group38% (92)Pelvic lymph node evaluation91% (221)Tumor grade 1 2 3: 34% (81) 42% (101) 24% (59)Depth of MMI (median)40% (range, 0-100)Cervical stromal involvement Cervical mucosal involvement7% (16) 2% (6)Lymphovascular invasion (LVI)20% (49) Open table in a new tab