(P 208) STEREOTACTIC ABLATIVE BODY RADIOTHERAPY FOR PEDIATRIC OSTEOSARCOMA LUNG METASTASES

Objective: Osteosarcoma is a rare, primary malignant bone tumor that accounts for only 3% of all childhood cancers. Patients with metastatic osteosarcoma have a 3-year survival rate of 20-45%, with pulmonary metastases being the most common site of spread. Pulmonary metastases are commonly treated with wedge resection for peripheral lesions; the 5-year survival for patients with solitary pulmonary metastases is roughly 30%. In patients with multiple metastases, it’s often difficult to justify surgical interventions, as such there is a need for minimally invasive treatments to provide patients with a life prolonging opportunity. Stereotactic Ablative Body Radiotherapy (SABR) is an effective and proven local therapy for lung metastases of various cancers. Hence, we evaluated the efficacy of SABR in pediatric patients with lung metastases from osteosarcoma, a histology commonly considered to be radioresistant. This is a report on a pilot study of SABR treatment for pediatric patients with more than one lung metastases and who were not deemed to be candidates for surgery.

Methods: The medical records of 3 pediatric patients with primary left distal femur osteosarcoma treated with SABR for their non-resectable lung metastases at time of relapse were reviewed. Primary endpoints were tumor response and adverse events. Secondarily, we analyzed overall survival which we defined as the date of first SABR treatment until the last clinic follow-up visit. Tumor volumes were measured using on the simulation CT scans prior to SABR treatment and on follow-up CT scans. Local control was evaluated using RECIST 1.1 criteria.

Results: We analyzed the results from 3 patients, all female, two age 17 and one age 23, harboring 9 pulmonary lesions treated with SABR. Median dose was 50 Gy ranging from 45-55 Gy in 5 fractions to the planning tumor volume (PTV). With a mean follow up time of 435 days, complete response rate was 33%, partial response 22%, stable disease 33%, and progressive disease 12%. There were no adverse events noted related to lung radiotherapy treatment including radiation pneumonitis. Two out of three patients were treated with concurrent targeted oral therapy. We defined concurrent therapy as being instituted within one month of SABR. One patient did not receive concurrent medical therapy, the second patient was receiving Pazopanib and the third Regorafenib. The mean overall survival from day 1 of SABR was 458.7 days (range 80-955 days). The patients died of disease 20, 56, and 73 months after diagnosis.

Conclusion: With an overall response rate of 88% (including stable disease), SABR provided a non-invasive effective palliative treatment option with few side effects in this pilot trial of 3 patients. A larger clinical trial is warranted to evaluate the role of SABR in the treatment of non-resectable metastatic sarcomas. The only complete response was noted anecdotally in the patient who received concurrent SABR and regorafenib. Therefore, additional studies are needed to determine optimal concurrent medical therapy as an adjunct to SABR.

Pulm Lesion Table.xlsx