PO05: The Utility of a Vaginal Brachytherapy Boost Following Pelvic External Beam Radiotherapy for Uterine Cancer

• Published in: Brachytherapy Vol. 22; no. 5; pp. S67 - S68
• Main Authors: Hazy, Allison, Ye, Hong, Mansour, Megan, Zureick, Andrew, Acosta-Torres, Stefany, Al-Wahab, Zaid, Gadzinski, Jill, McCool, Kevin, Rosen, Barry, Nandalur, Sirisha, Jawad, Maha Saada
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.09.2023
• ISSN: 1538-4721; 1873-1449
• DOI: 10.1016/j.brachy.2023.06.106

In the setting of adjuvant uterine cancer treatment, the indications for a vaginal brachytherapy boost (VBB) in addition to pelvic external beam radiation (EBRT) are not well described. The use of a VBB remains largely institutional- and physician-dependent. Current recommendations for VBB are not well supported or standardized; rather, they are often based on risk factors for a local recurrence. Here, we examine outcomes for uterine cancer patients treated with adjuvant EBRT followed by a VBB. We identified patients with stage I-III uterine cancer treated at our institution with adjuvant EBRT and a VBB from 1998-2021. A retrospective review was performed to identify patient and tumor characteristics and treatment details. Pelvic EBRT was prescribed to 45-50.4 Gy in 1.8-2 Gy per fraction. A sequential, high-dose rate VBB was delivered via a vaginal cylinder prescribed either to surface or to a depth of 5 mm, to a dose of 10-20 Gy in 2-4 fractions. We identified risk factors for vaginal cuff recurrence as: high grade disease, lymphovascular space invasion (LVSI), deep (outer half) myometrial invasion, lower uterine segment involvement, cervical stromal involvement, and positive surgical margins. Clinical endpoints analyzed were local control (LC), loco-regional control (LRC), distant metastases (DM), disease free survival (DFS), and overall survival (OS). Univariate (UVA) and multivariate analyses (MVA) were used to identify predictors for the clinical endpoints. 86 patients were identified and included, with a median age of 65 (33-86) at diagnosis. The median follow up was 7.2 years (0.35-18.6). Forty patients (46%) had high grade disease, 62 (72%) had LVSI, 63 (73%) had deep myometrial invasion, 54 (63%) had cervical stromal involvement, five (6%) had lower uterine segment involvement, and two (2%) had positive surgical margins (paracervical margin). At 5 years, the LC rate was 89.6%, LRC was 82.3%, DM was 27.7%, DFS was 57.1%, and OS was 69.5%. On UVA, high grade disease was significant for all outcomes. However, LVSI, deep myometrial invasion, lower uterine segment involvement, cervical stromal involvement, and positive surgical margins were not found to be significant. On MVA, high grade disease remained a significant factor for OS with a hazard ratio of 3.05 [1.40-6.65] (p=0.005). Patients at our institution with stage I-III uterine cancer treated with adjuvant pelvic EBRT followed by a VBB had at least one high risk feature (detailed above). Excellent vaginal and pelvic control rates were seen at 5 years. High-grade histology is a significant risk factor that warrants further exploration along with genomic evaluation. Additional study evaluating toxicity following this treatment regimen is currently ongoing. Further investigation is warranted to compare outcomes and toxicity for appropriately matched patients receiving adjuvant treatment with pelvic EBRT alone compared with EBRT plus VBB.