(P23) Toxicity of Post-Operative Intensity Modulated Radiation Therapy in Patients With Endometrial Cancer

Abstract

The purpose of this study was to evaluate the acute and late genitourinary (GU) and gastrointestinal (GI) toxicity of post-operative intensity modulated radiation therapy (IMRT), delivered in 160cGy daily fractions, for patients with endometrial cancer. This retrospective study included 103 patients treated between 2006-2016 for endometrial cancer. All patients underwent a surgical staging with central review of pathology. Indications for post-operative IMRT included histology subtype, histological grade, advanced age, lymphovascular space invasion, depth of myometrial invasion, and/or lymph node involvement. All patients received IMRT interdigitated with weekly high-dose rate intracavitary brachytherapy (BT). The median IMRT dose, delivered in 160 cGy daily fractions, was 5120 cGy (range, 3520-5120). The median BT dose prescribed to the vaginal surface, delivered in six weekly fractions, was 2400 cGy (range, 1200-4800). A total of 86 (78%) patients received chemotherapy at the discretion of the treating gynecologic oncologist. The rate of GU and GI toxicities, overall survival (OS), distant free survival (DFS), and local control (LC) were calculated via Kaplan-Meier method. The log-rank test and Cox proportional hazard models were used to evaluate the impact of collected parameters on OS. The median follow-up was 25.2 months (range, 1.3-25.2). The median age at diagnosis was 61 years (range, 36-85). The FIGO pathologic stages were IA in 6 patients, IB in 11, IC in 13, II in 8, IIIA in 2, IIIC1 in 39, and IIIC2 in 24 patients. Histological subtypes included endometrioid adenocarcinoma (n=68), carcinosarcoma (n=14), clear cell (n=2), serous (n=9), and mixed histology (n=10). There were no acute grade > 3 GU or GI toxicities as well as no late grade > 3 GU toxicities. Late grade > 3 GI toxicity occurred in 2 patients; both developed a small bowel obstruction (SBO) with one requiring surgical intervention and the other requiring gastrostomy tube placement. Both of these patients received concurrent chemotherapy. The 2-year actuarial rate for grade ≥3 GI toxicity was 2.5%. The 2-year actuarial rates for OS, DFS, and LC were 84.7 %, 69.8% and 87.1%, respectively. On multivariate analysis non-endometrioid histology (HR 2.53, 95% CI 0.97-6.91, p = 0.07) was predictive of worse OS. Post-operative IMRT for endometrial cancer patients delivered in 160 cGy daily fractions is associated with excellent outcomes and limited rates of radiation-related GU and GI toxicities.