High-Dose-Rate Brachytherapy for Vaginal Rhabdomyosarcoma (RMS): Lessons Learned at a Single Institution

Abstract

Botryoid RMS is a rare pediatric tumor most commonly arising within the vaginal wall of girls under age three. Most patients are successfully treated with low-risk chemotherapy protocols but local treatment is required to minimize risk of local relapse. Intravaginal brachytherapy is an effective local therapy that can minimize sequelae in these very young patients. We reviewed records of all patients with RMS who received intravaginal high-dose-rate brachytherapy from 2010-2022 at a single institution. All were treated with multiagent chemotherapy with or without minor surgical procedures, and had no gross disease prior to intravaginal brachytherapy. All patients underwent CT simulation under anesthesia and optimal-sized cylindrical applicators were chosen based on patient anatomy. Twelve girls, median age 23 months (range 3-33), were treated with daily anesthesia. All were Stage 1 and 92% had Group III disease. A single patient had Group IIA disease based on up-front resection. Early in the series, 5 patients received 21 Gy in 7 fractions according to COG protocol guidelines. Subsequent patients received higher doses of 28-30 Gy in 7-10 fractions. Custom sized cylinders were used with diameters ranging from 1.2-1.6 cm and dose was prescribed to a median depth of 3 mm. Median mean dose to the rectum, bladder, uterus, and bilateral ovaries was 8.7 Gy, 7.2 Gy, 6.9 Gy, and 5.0 Gy, respectively. Median follow-up was 4 years (range 1-10). No acute or late side effects have occurred. At follow-up, three girls were of pubescent age, all three exhibited signs of puberty and two had reached menarche. Three girls (25%) suffered local relapse at a median of 15 months (range 5-16 months) after brachytherapy. One-year and five-year local control rates were 92% (95% CI 54-99%) and 70% (95% CI 32-89%), respectively. All relapses were in patients receiving 21 Gy and two were beyond full dose coverage of brachytherapy at the introitus and in the uterus. Subsequent patients receiving higher doses and full coverage of the vagina have had no local failures. Two of three patients who failed were cured with salvage therapy resulting in one-year and five-year overall survival rates of 100% and 86% (95% CI 33-98%), respectively. Intravaginal high-dose-rate brachytherapy is an excellent option for local control of vaginal RMS with fewer long-term risks than external beam proton therapy or radical surgery. A dose of 28 Gy in 7 fractions prescribed to the entire vagina is necessary for optimal prevention of relapse. Longer follow-up is needed to confirm preservation of ovarian, reproductive, and sexual function.