PURPOSE This study aimed to report on the institutional outcomes after proton therapy for pelvic rhabdomyosarcoma (RMS). METHODS AND MATERIALS Thirty-one children (≤21 years old) with group III pelvic RMS were enrolled on a prospective outcome study and treated between 2007 and 2018. Patients with vaginal/cervical RMS were excluded. The median age was 2.6 years. Twenty-four patients had embryonal RMS. At diagnosis, the median tumor volume was 185 cm3 and the median maximum diameter was 9.4 cm. Seven patients had N1 disease. Nineteen and 12 patients received European Pediatric Soft Tissue Sarcoma Study Group- and Children's Oncology Group-based chemotherapy, respectively. Fourteen patients underwent resection of the primary tumor after induction chemotherapy, including 6 patients who had a total cystectomy. The median radiation dose was 50.4 Gy relative biological effectiveness. RESULTS With a median follow-up of 4.2 years, the 5-year local control, progression-free survival, and overall survival rates were 83%, 80%, and 84%, respectively. Patients <3 years old had better local control (100% vs 68%; P = .02), and patients with embryonal histology had better survival (96% vs 54%; P = .02). No other factors were significantly associated with disease control or survival. Specifically, no statistically significant difference was observed in local control, progression-free survival, or overall survival when comparing patients who underwent biopsy versus gross total resection (75% vs 93%, 68% vs 93%, 75% vs 93%, respectively). Excluding patients who underwent cystectomy, urinary toxicity was limited to 2 patients with nocturnal enuresis. Exploratory surgery to address a persistent mass or thickened bladder wall after radiation was the most common source of serious toxicity. CONCLUSIONS This cohort of young children with large pelvic tumors treated with proton therapy demonstrates similar local control with less toxicity than historic reports. Functional bladder preservation is possible in most patients. Exploratory biopsy in the 18 months after radiation should be approached with caution.

中文翻译：

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质子疗法治疗III组骨盆横纹肌肉瘤的结果。

目的本研究旨在报告质子治疗盆腔横纹肌肉瘤（RMS）后的机构疗效。方法和材料2007年至2018年，对31例年龄≤21岁的第三组骨盆RMS的儿童进行了一项前瞻性研究，并对其进行了治疗。阴道/宫颈RMS的患者被排除在外。中位年龄是2.6岁。24例患者具有胚胎RMS。在诊断时，中位肿瘤体积为185 cm3，中位最大直径为9.4 cm。7例患者患有N1疾病。分别有19例和12例患者接受了欧洲儿科软组织肉瘤研究组和儿童肿瘤学组的化疗。诱导化疗后有14例患者接受了原发性肿瘤切除，其中6例行了全膀胱切除术。中值辐射剂量为50。4 Gy相对生物学有效性。结果中位随访期为4.2年，其5年局部控制率，无进展生存期和总生存率分别为83％，80％和84％。<3岁的患者具有更好的局部控制（100％vs 68％； P = .02），具有胚胎组织学的患者具有更好的生存率（96％vs 54％； P = .02）。没有其他因素与疾病控制或生存显着相关。具体而言，当比较接受活检与总切除的患者时，局部控制，无进展生存期或总生存期无统计学差异（分别为75％对93％，68％对93％，75％对93％） ）。除进行膀胱切除术的患者外，尿毒症仅限于2例夜间遗尿症患者。放射治疗后持续性肿物或膀胱壁增厚的探索性手术是最常见的严重毒性反应。结论该队列研究表明，质子疗法治疗的盆腔大肿瘤患儿具有相似的局部控制作用，且毒性低于历史报道。大多数患者可以进行功能性膀胱保存。放疗后18个月应进行探查活检。