3523 - Eight-Year Results of a Phase II Prospective Trial of Proton Therapy for Non-Metastatic Pediatric Non-Rhabdomyosarcoma Soft Tissue and Bone Sarcomas

S. Kang¹, B. Bajaj¹, K. W. Allison¹, C. B. Hess^1,2, B. Y. Yeap³, J. Marinelli⁴, S. M. MacDonald¹, K. J. Marcus⁵, M. Huang⁶, A. Friedmann⁶, D. H. Ebb⁷, T. F. DeLaney¹, Y. L. E. E. Chen¹, N. J. Tarbell¹, and T. I. Yock¹; ¹Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, ²Department of Radiation Oncology, Winship Cancer Institute, Atlanta, GA, ³Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, ⁴Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, Boston, MA, ⁵Department of Radiation Oncology, Brigham and Womens Hospital/Dana-Farber Cancer Institute, Boston, MA, ⁶Department of Pediatric Hematology/Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, ⁷Department of Pediatric Hematology & Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA

Purpose/Objective(s): This prospective phase II trial was designed to assess disease control and late effects following proton radiotherapy in children and young adults with non-metastatic Ewing Family of Tumors (EFT) or other bone sarcomas and non-rhabdomyosarcoma soft tissue sarcomas (NRSTS). Materials/

Methods: Sixty-nine pediatric and young adult patients (age<30) with NRSTS or bone sarcomas were enrolled between September 2006 and July 2016. Chemotherapy and surgery were administered to patients in accordance with current standard practices or according to co-enrollment on cooperative group protocols.
Results: Median follow-up was 7.7 years (range 0.4-15.7). 39 patients had EWS sarcoma, 5 patients had osteosarcoma, and 25 patients had other histologies. Eight-year overall survival (OS), event-free survival (EFS), local regional control (LC), and distant control (DC) rates for the whole cohort were 77.5%, 67.2%, 82.1%, and 87.9%, respectively and 81.0%, 76.8%, 92.3%, and 89.7% for EWS and 73.2%, 56.5%, 69.7%, and 86.3% for other histologies. The median age at the time of radiation therapy was 12.3 years (range 1-22). The most common primary tumor locations were head and neck (42%); abdomen/pelvis (26%) and paraspinal (23%). Seventy percent of patients had gross residual disease at the time of radiotherapy. The median radiation dose was 55.8GyE (range 41.4-72). Patients with a GTR had no difference in EFS (8-year: 69.9% vs 65.8%, p=0.9) or LC (8-year: 74.7% vs 85.3%, p=0.4). The non-significant relationship between surgical extent and EFS/LC did not change across histology (among EWS, 8-year EFS was GTR: 85.7% vs STR 75.0%, p=0.6 and 8-year LC was GTR: 85.7% vs STR 93.8%, p=0.5; among all other histologies, 8-year EFS was GTR: 64.3% vs STR 49.2%, p=0.6 and 8-year LC was GTR: 71.4% vs STR 68.8%, p=0.8). Eight-year follow-up toxicity assessments showed 22 patients (31.9%) with at least one grade 2 toxicity and 13 patients (18.8%) with at least one grade 3 toxicity, both at least partially attributable to radiation therapy. There were no grade 4 toxicities reported.
Conclusion: Eight-year OS, EFS, LC, and DC rates were similar to those observed in comparable studies of photon radiation. Proton radiation represents a safe and effective radiation modality for pediatric non-rhabdomyosarcoma bone and soft tissue sarcomas.