Stereotactic Body Radiation Therapy for Pediatric, Adolescent, and Young Adult Patients With Osteosarcoma: Local Control Outcomes With Dosimetric Analysis.
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BACKGROUND/OBJECTIVES: Osteosarcoma is a radioresistant tumor that may benefit from stereotactic body radiation therapy (SBRT) for locoregional control in metastatic/recurrent disease. We report institutional practice patterns, outcomes, toxicity, and failures in osteosarcoma patients treated with SBRT. DESIGN/METHODS: We reviewed cases of recurrent/metastatic osteosarcoma treated with SBRT from 2015 to 2023. Outcomes included local control, overall survival (OS), and toxicity. Local failures (LFs) were categorized as in-field (≥80% of recurrence within the 95% isodose line), marginal (20%-80%), or out-of-field (<20%). RESULTS: Twenty-four patients (71 lesions) met eligibility. Mean imaging follow-up was 5.9 months (range, 0.6-57.1), and overall mean follow-up was 10.7 months (2.8-57.6). Lesions were osseous (66%), parenchymal (17%), or soft tissue (17%). Median SBRT dose was 40 Gy/5 fractions (range, 16-60 Gy in 1-5 fractions); 32 lesions received concurrent chemotherapy. Eleven LFs occurred: 4 in-field, 3 marginal, and 4 out-of-field. The 6- and 12-month cumulative LF incidences were 10.3% (95% CI 4.5-18.9) and 13.6% (95% CI 6.6-23.2). On multivariable analysis, spine SBRT (HR 3.39, 95% CI 1.03-11.14) and larger planning target volume (HR 1.003, 95% CI 1.001-1.006) were associated with LF. The 6- and 12-month OS rates from first treatment were 87.5% (95% CI 66.1-95.8) and 64.1% (95% CI 40.6-80.3). Grade 2 acute toxicity occurred in 5.6% of cases with no acute grade ≥3 events. CONCLUSIONS: SBRT for recurrent/metastatic osteosarcoma is safe and effective, achieving a 13.6% 1-year LF rate. LFs were evenly distributed amongst in-field, marginal, and out-of-field. Spine SBRT had the highest LF risk, suggesting the need for tailored strategies near critical structures.