Encouraging Local Control With Pediatric Spatially Fractionated Radiation Therapy

Purpose Spatially fractionated radiation therapy (SFRT) is a promising treatment involving the delivery of discrete spheres of high-dose radiation, potentially enhancing treatment response. Despite encouraging results for adult patients, no SFRT data exist in pediatric patients. Methods and Materials All pediatric patients receiving radiation therapy from 2019 to 2025 with at least 1 follow-up imaging study were considered. Patient characteristics and outcomes were recorded via institutional review board–approved retrospective chart review. Results Five pediatric patients who received SFRT were identified, with a median age of 15.7 years (range, 6.5-17.2 years). Three were alive at last follow-up (median, 13 months; range, 3-18 years). Neither tumor progression nor grade ≥ 2 toxicity was identified at SFRT sites. One recurrent wound infection occurred after enoxaparin sodium injection in the high-dose radiation therapy field. Two patients received upfront SFRT for pelvic osteosarcoma, followed by 74.8 Gy in 34 fractions and 69 Gy in 30 fractions. The treatment volume was over 600 cm 3 in both cases, allowing for delivery of 26 and 46 high-dose spheres. Both patients remain alive with primary tumor control; however, both have metastatic disease. Three other cases treated metastatic and/or recurrent disease: Ewing sarcoma, anaplastic ependymoma, and renal cell carcinoma. Sites included chest wall (n = 2), lung (n = 5), and pelvis (n = 1). One patient had 4 courses of SFRT, including 3 small lung volumes < 20 cm 3 allowing delivery of 2 to 5 spheres per treatment. Conclusions We present one of the first case series of SFRT in pediatric patients, with favorable local control and toxicity results. Further study of SFRT for radioresistant or recurrent tumors is required.