Image Guided Brachytherapy for Pediatric Bladder and/or Prostate Rhabdomyosarcoma: Toward an Increased Personalization of Treatment.

Purpose: Rhabdomyosarcoma (RMS) is the most common soft tissue cancer in children. Around 15% of RMS involve the bladder and/or prostate (BP). Overall survival is around 85%. After chemotherapy, patients receive local treatment based on surgery and/or radiation therapy. In recent decades, image guidance and pulsed-dose rate (PDR) brachytherapy have made it possible to personalize treatment and reduce radiation-related toxicity while maintaining good tumor control. We report one of the largest series of image guided brachytherapy for pediatric RMS BP.

Methods And Materials: The clinical and dosimetric parameters of children treated with brachytherapy for BP RMS between July 2014 and September 2020 were retrospectively reviewed. Patients were treated with a multimodal conservative approach, combining partial conservative surgery (preservation of the bladder neck and urethra), followed by an interstitial brachytherapy procedure. Iridium-192 PDR treatment was administered on the basis of computed tomography and magnetic resonance imaging planning. Toxicities were reported according to version 4.0 of the Common Terminology Criteria for Adverse Events.

Results: A total of 75 patients were identified, with a median age of 29 months (range, 2-84) at diagnosis. The median brachytherapy dose was 60.06 Gy (143 pulses, 0.42 Gy/pulse). With a median follow-up of 44.1 months (range, 0.7-90), the 5-year overall survival and progression-free survival rates were 97.3% and 92%, respectively. Median D for the bladder and D for the rectum were 38.6 Gy and 49 Gy, respectively. The 5-year probability of survival without severe late urinary toxicity (grade 3 or higher) was estimated at 78.8% (95% CI, 68.1-91.1). A total of 9.3% of children experienced grade 2 or 3 late rectal toxicity.

Conclusions: Image guided PDR brachytherapy offers personalized treatment for pediatric BP RMS, with a favorable therapeutic index. No prognostic factors for urinary toxicity have been identified. Multicenter studies with larger numbers of patients are needed to clarify these data.