3530 - Hybrid Intracavitary-Interstitial High-Dose-Rate Brachytherapy for Vaginal Recurrence from Endometrial Cancer

P. Kumar¹, Y. Gokun², T. Andraos¹, and A. M. Quick¹; ¹Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, OH, ²Center for Biostatistics, Department of Biomedical Informatics, The Ohio State University Wexner Medical Center, Columbus, OH

Purpose/Objective(s): Salvage radiation therapy with brachytherapy (BT) +/- external beam radiotherapy (EBRT) is preferred treatment for locally recurrent endometrial cancer (EC). For bulky tumors (= 5 mm), interstitial brachytherapy (ISBT) is preferred for optimal target coverage and OAR sparing but is more complex, invasive, labor and source intensive. We sought to report clinical outcomes and dosimetric analysis of image guided hybrid intracavitary-interstitial (IC/IS) BT for treatment of EC with vaginal recurrence as an alternative approach to ISBT. Materials/

Methods: Institutional database was used to identify patients with EC vaginal recurrence treated using combined IC/IS high-dose-rate (HDR) BT +/- EBRT from 2021-2023. Hybrid brachytherapy was delivered using a technology company universal interstitial cylinder. Applicator insertion was done under general anesthesia. CT and MRI guidance was used to confirm applicator position, delineate target/OARs, and plan 3-dimensional treatment. The dose was prescribed to the high-risk CTV. Treatment was delivered using remote afterloader with Ir-192. Kaplan-Meier method was used to calculate survival estimates.
Results: We identified 10 patients who received HDR BT using IC/IS applicator for EC vaginal recurrence. Median age at initial diagnosis was 65 years. Clinical characteristics are presented in table 1. All patients completed hybrid BT treatments. Most patients (8/10) received pelvic EBRT 45Gy in 25 fractions before BT. Median BT dose was 21Gy most commonly delivered in 3 fractions. Median total EQD2_10 dose to high-risk CTV was 33.90Gy (range 6.90-47.40) for BT alone and 77.10Gy (range 35.10-97.40) for combined EBRT/BT. Respective median total EQD2_3 doses to 2 cc of rectum, bladder, sigmoid colon were 7.05Gy, 10.75Gy, 6.95Gy from BT alone and 50.25Gy, 55.45Gy, 50.85Gy from combined EBRT/BT. Median follow-up after BT was 14.28 months and 6 out of 10 patients were free from loco-regional disease at last follow up. One-year loco-regional PFS was 63% (95% CI: 23%-86%). At last follow-up 7 out of 10 patients were alive. There was no grade >2 toxicity.
Conclusion: Hybrid intracavitary/interstitial brachytherapy is a promising and safe treatment option for vaginal recurrence of endometrial cancer with good local control and acceptable toxicity. To our knowledge, this is the first report of use of hybrid IC/IS BT for treatment of vaginal recurrence from EC.

Abstract 3530 – Table 1

Characteristic	Number of patients
Initial stage IA IB IIA	8 1 1
Initial grade 1 2 3	8 1 1
Adjuvant RT after initial surgery No Vaginal brachytherapy alone EBRT+Vaginal brachytherapy	7 2 1
Recurrence site prior to hybrid brachytherapy Vagina Locoregional Vagina + Distal	7 2 1
Systemic therapy prior to hybrid brachytherapy Yes No	5 5
EBRT with hybrid brachytherapy Yes No	8 2
Pelvic EBRT dose 45Gy in 25 fractions SIB 55Gy to gross nodes 14Gy boost to vaginal disease	6 1 1
Concurrent chemotherapy with EBRT Yes No	2 8