2841 - Long Term Outcomes of the First 100 Patients Treated with Vaginal Electronic Brachytherapy in the Management of Endometrial Cancer

Purpose/Objective(s): We evaluated long-term vaginal toxicity and disease outcomes in women treated with vaginal electronic brachytherapy (EBT) following surgical management of endometrial cancer.

Materials/Methods: Women with endometrial cancer treated with adjuvant EBT were included in this study. Women diagnosed with uterine cancer of high-risk histology or advanced stage received EBT following completion of adjuvant chemotherapy. EBT was performed using a miniature low-energy (50-kV peak) X-ray source with a single-channel vaginal cylinder applicator to deliver radiation to the vagina along a specified length of the cylinder. EBT was delivered either as monotherapy or as a sequential boost following completion of pelvic external beam radiation (EBRT). EBT was delivered to 4 cm treatment length prescribed as 7 Gy to 5 mm depth x 3 fractions or 6 Gy to vaginal surface x 5 fractions in the EBT alone group or 6 Gy to vaginal surface x 3 fractions in the EBT boost group. Following completion of EBT, patients were evaluated for toxicities and recurrences. In this study, treatment related vaginal toxicity (atrophy/stenosis) was scored according to the Common Terminology Criteria for Adverse Events version 5.0. Multivariable analysis (MVA) of prognostic factors was performed with Cox Proportional-Hazards Model using data management and decision management software, and disease-free survival (DFS) and overall survival (OS) were estimated from date of surgery with Kaplan-Meier Method using R 4.3.0 software.

Results: 100 women were treated from 12/2017-12/2020 with EBT following hysterectomy. Median age of the cohort was 68 years (range, 30-88 years). 59 presented with endometrioid histology. 44 received adjuvant chemotherapy. 29 presented with at least stage II disease, and 28 received EBRT prior to EBT boost. EBT was delivered over a median interval of 1.3 weeks (range, 0.3-3.1 weeks). At a median follow-up of 55.0 months (range, 7.0-82.3 months), no patients were found to have = grade 3 vaginal toxicity. The cumulative risk of developing gr 1 and 2 vaginal toxicity at 48 months was 40%. 1 vaginal cuff recurrence, 1 locoregional recurrence, and 12 distant recurrences were observed. Advanced tumor stage, cervical stroma involvement, & treatment with EBRT were associated with inferior DFS without adjustment of confounding variables. After adjusting for all confounding variables, advanced tumor stage was significantly associated with inferior DFS on MVA. DFS at 19 & 38 months were 91.9% and 83.6%, respectively. OS at 19 & 38 months were 93.9% & 88.7%, respectively.

Conclusion: EBT appears to be a safe, well-tolerated, and a promising alternative treatment option to traditional vaginal brachytherapy using a radioactive source. One local recurrence was observed at 55 months follow-up. Cumulative risk of developing vaginal toxicity, DFS, and OS, following treatment with EBT in this heterogeneous population appears to be acceptable and comparable to patients treated with vaginal brachytherapy in PORTEC 2.