Updated Results of Proton Radiation Therapy for Pediatric Rhabdomyosarcoma Phase II Trial

To report updated enrollment and 5-year survival and disease control data in children with rhabdomyosarcoma (RMS) treated with proton radiation therapy on an institutional prospective phase II study. Seventy-five patients with localized RMS (<21 years) or metastatic embryonal RMS (2-10 years) were enrolled between 1/2005 and 11/2017. All patients were treated with either neoadjuvant or concurrent chemotherapy regimens of vincristine, actinomycin, and cyclophosphamide; or vincristine, actinomycin, and ifosfamide, and proton radiation. Surgical resection was based on tumor site and accessibility. Adverse effects of treatment were assessed and graded using CTCAE version 3.0. Patients were allowed concurrent enrollment onto Children's Oncology Group or European Pediatric Sarcoma Study Group protocols. Since last reported, median follow-up for survivors increased from 47 to 67 months (range, 1 to 176 months). Five-year event-free survival (EFS), overall survival (OS), and local control (LC) with this additional enrollment and follow-up are 67%, 77%, and 76% respectively, compared to 69%, 78%, and 81% at last reporting. The 5-year LC rates by Children’s Oncology Group risk classification were 94% and 70% for low- and intermediate-risk groups, respectively, compared to previous rates of 93% and 77%. There were 18 patients with grade 3 acute toxicities and 6 patients with grade 3 late toxicities. No patients experienced acute or late grade 4 toxicities. With more comprehensive and durable clinical follow-up data, five-year EFS, OS, and LC rates remain similar to those observed in trials of pediatric RMS patients treated with photon radiation. Treatment of pediatric RMS with proton radiation is well tolerated and an effective radiation therapy modality.