Clinical Outcomes and Efficacy of Stereotactic Body Radiation Therapy in Metastatic Pediatric Solid Tumors

Purpose/Objective(s) Pediatric patients with metastatic solid tumors historically have a poor overall survival. Some pediatric patients may still be potentially curable with aggressive local therapy to metastatic disease, and adult trials have defined a group of oligometastatic patients, where the use of stereotactic body radiation therapy (SBRT) has an overall survival benefit. The purpose of this study is to report results of the use of SBRT in the treatment of pediatric metastatic disease. Materials/Methods All pediatric and adolescents and young adult (AYA) patients age 3-40 years who received SBRT were included between the years 2000-2020. SBRT included radiation treatments with 3-5 fractions and ablative doses above conventional palliative radiation. Study endpoints included local control (LC), progression free survival (PFS), overall survival (OS), cumulative incidence (CI) of death or local failure and toxicity. The endpoints with respect to survival and LC were calculated using the Kaplan-Meier estimate. The cumulative incidence of local failure was calculated using death as a competing risk. Toxicity was scored using CTCAE v5.0. Results Thirty-six lesions in 16 patients were treated with SBRT and comprised the overall cohort. The most common pediatric solid tumors treated were Ewing's Sarcoma (n = 3), Osteosarcoma (n = 3), and Rhabdomyosarcoma (n = 2). The majority of lesions irradiated were in the spine (n = 11), lung (n = 8), pelvis (n = 7), and brain (n = 5). The median follow up was 12 months. The median OS and PFS for the entire cohort were 17 months and 15.7 months, respectively. Patients were treated to a median dose of 25 Gy in 5 fractions. The 1-year OS for the entire cohort was 75%. The 6- and 12-month local control was 85% and 78%, respectively. There were no local failures in irradiated lesions for patients who received a BED10≥100 Gy. Patients treated with SBRT who had ≤5 metastatic lesions at first recurrence had a superior 1-year OS of 100% versus 50% for those with > 5 lesions. No patients experienced a grade 4 or 5 toxicity in our cohort. One patient (6.3%) experienced a CTCAE grade 3 toxicity (seizure) which resolved after anti-epileptic medications. Conclusion Local control was excellent with SBRT delivered to metastatic disease, particularly for lesions receiving a BED10≥100 Gy. High-grade toxicity was rare in our patient population. Patients with 5 or fewer metastatic sites have a significantly better OS compared to > 5 sites. Future prospective trials with multi-institutional collaboration will be necessary to evaluate appropriate patient selection and the optimal radiation dose regimen.