Definitive Radiation Therapy for Ewing Sarcoma: Outcomes Based on Tumor Volume, Dose, and Fractionation

Purpose

Dose escalation for definitive radiation therapy (DE-RT) in larger Ewing sarcomas (ESs) is associated with a lower risk of local recurrence. We report treatment and toxicity outcomes in ES tumors treated with DE-RT, including hypofractionated approaches and size stratification of analysis.

Methods and Materials

A retrospective review of ES patients treated with DE-RT to doses ≥55.8 Gy was performed. Local failure (LF) with death as a competing risk was assessed. Maximally selected rank statistics were used to determine the optimal stratification of patients by survival using tumor size measurements.

Results

In total, 47 patients were analyzed. Twenty-eight patients (59.6%) received DE-RT, of which 6 received hypofractionation. For DE-RT, median equivalent dose in 2 Gy fraction for α/β = 10 was 60 Gy (range, 56.2-62) with conventional fractionation and 62.2 Gy (range, 56.5-67.1) with hypofractionation. Empirically derived size cutoffs identified a subgroup of ultralarge tumors at higher risk of LF defined as >11.8 cm in the longest direction, 569.2 cm³ prechemotherapy volume, or 288.9 cm³ postchemotherapy volume. Five-year cumulative incidence of LF was lower in patients treated with DE-RT at 11.7% (95% CI, 3.16%-43.6%) versus 35.6% for non-DE-RT (95% CI, 17.4%-72.61%; P = .098). Multivariate analysis showed trends toward DE-RT benefiting tumors of all sizes and stages.

Conclusions

DE-RT was associated with a trend toward better LF in all tumors without toxicity or plan quality changes. Ultralarge tumors demonstrated poor LF rates and necessitate further study.