As radiation therapy (RT) for Wilms tumor (WT) evolves with more conformal techniques, it is necessary to evaluate patterns of failure and toxicity. We sought to determine the rate of local failure (LF) after abdominal RT in WT, specifically focusing on those with contained rupture treated with whole abdominal and pelvic RT (WAPRT) vs flank RT. Secondary objectives were to determine overall survival (OS), distant failure (DF), and late toxicities.

A single institution retrospective study of 54 pediatric patients with WT treated with abdominal RT between May 2000 and October 2022. LF and DF were calculated through cumulative incidence function and OS by Kaplan-Meier method.

The median age was 4.5 years and the median follow-up was 6 years. Most patients (91%) had favorable histology. Only 1 patient experienced LF, 15 months from completion of RT (cumulative incidence 2% at 5 y). All patients who received unilateral flank radiation for contained rupture/spillage (n=13) experienced long-lasting intra-abdominal tumor control. A total of 5 patients experienced a DF at a median of 7 months, all in the lung. No patient relapsed in the lungs after upfront whole lung irradiation (n=16). OS was 96% at 5 years. Among 28 patients who followed through puberty, 4 female patients with prior WAPRT experienced hormonal irregularities/infertility.

Unilateral flank radiation may be a viable alternative to WAPRT for contained rupture/spillage and should be further explored prospectively. Our results may also be utilized in the future for outcome and toxicity comparison as conformal radiation techniques evolve.