Multimodal conservative local treatment based on combined brachytherapy and external beam radiation therapy for paediatric pelvic and perineal rhabdomyosarcoma.

[PURPOSE] In pediatric pelvic or perineal rhabdomyosarcoma, organ preservation rates are high following neoadjuvant chemotherapy. We assessed the impact of combining external beam radiation therapy (EBRT) and brachytherapy (BT) on local control and functional outcomes.

[METHODS] We retrospectively analyzed records of all children who received both EBRT and a BT boost in our department from 2005 to 2023. Data collected included tumor relapse, local control, survival and late toxicity rates. Treatment was administered as part of a multimodal conservative radio-surgical approach.

[RESULTS] Eighteen patients were identified, with a median age of 4 years (range, 2.9 - 8.6 years). According to the Intergroup Rhabdomyosarcoma Study (IRS) risk groups, 10 patients were classified as IRS-III and 8 as IRS-IV. Seven patients had metastases at diagnosis. The median number of chemotherapy cycles prior to local treatment was 8 (range, 5-10). Nine patients (50 %) underwent prior conservative surgery, followed by radiation therapy consisting of both BT and EBRT. This combination was indicated for at least one the following reasons: nodal invasion (n = 11, 61 %), risk of peritoneal dissemination (n = 3, 17 %) and/or local extension (n = 7, 39 %). The median prescribed dose was 20 Gy (range 12-30 Gy) for BT and 50.4 Gy (range, 18.8-55 Gy) for EBRT. Two patients were treated with HDR BT, while the remaining received LDR (n = 4) or PDR (n = 12).The median follow-up period was 4.6 years (range, 2.9-6.6 years). At the last follow-up, failure free-survival was 67 %, local control was 78 % and overall survival was 83 %. Four patients experienced grade II late urinary toxicities, including dysuria or incontinence in two patients. One patient required secondary cystectomy, and another received botulinum toxin injections in the bladder neck.

[CONCLUSION] Organ preservation with favorable functional outcome can be achieved in pelvic and perineal rhabdomyosarcoma by combining BT and EBRT, with or without prior surgery. This approach requires close collaboration to develop customized radiation therapy plans. Extended follow-up is necessary to assess long-term functional outcomes.