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

Area of Science:

• Radiation Oncology
• Pediatric Oncology
• Medical Physics

Background:

• Ewing sarcoma (ES) treatment aims to minimize local recurrence.
• Dose escalation for definitive radiation therapy (DE-RT) may improve local control in larger ES.
• Understanding the impact of tumor size on DE-RT outcomes is crucial.

Purpose of the Study:

• To evaluate treatment and toxicity outcomes of DE-RT in ES.
• To assess the impact of tumor size on local failure (LF) after DE-RT.
• To analyze outcomes with conventional and hypofractionated DE-RT approaches.

Main Methods:

• Retrospective review of 47 ES patients treated with DE-RT (≥55.8 Gy).
• Analysis of local failure (LF) using competing risks.
• Tumor size stratification using maximally selected rank statistics.

Main Results:

• DE-RT was administered to 28 patients, including 6 with hypofractionation.
• Median equivalent dose (Gy) for DE-RT was 60 Gy (conventional) and 62.2 Gy (hypofractionation).
• Ultralarge tumors (>11.8 cm, >569.2 cm³ pre-chemo, or >288.9 cm³ post-chemo) showed higher LF risk.
• Five-year cumulative incidence of LF was 11.7% for DE-RT vs. 35.6% for non-DE-RT (P=.098).

Conclusions:

• DE-RT demonstrated a trend toward improved local control without increased toxicity.
• Ultralarge ES tumors represent a subgroup with poor local failure rates.
• Further research is needed to optimize DE-RT for ultralarge ES tumors.