Long-term locoregional control and pattern of recurrences after implementation of highly conformal flank target volumes and image-guided Intensity-Modulated Arc Therapy for pediatric Wilms tumors

INTRODUCTION: Excellent outcomes in Wilms tumors (WT) have allowed efforts to reduce toxicity and treatment burden while sustaining effectiveness. Concerning radiotherapy, 'conventional' flank target volumes combined with two opposing photon beams are now being replaced by highly conformal flank target volumes combined with image-guided Intensity Modulated Arc Therapy (IMAT), allowing better sparing of the organs at risk, but outcome descriptions based on large cohorts are scarce. Previously a cohort of 36 patients with excellent locoregional control at 2 years from diagnosis using 'modern' flank irradiation has been described. This study aims to investigate locoregional control outcomes, patterns of recurrence, and toxicity in an extended national cohort of WT with a longer follow-up period. MATERIALS AND METHODS: : ≤19.9%). RESULTS: Seventy patients received post-operative flank irradiation only (n=50) or combined with metastatic site irradiation (n=20). With a median follow-up of 4.7 years, the estimated 4-year LCR, DFI, EFS, and OS were 93.7%, 86.4%, 83.7% and 93.7%, respectively. Four patients developed a locoregional recurrence, of whom one (marginal recurrence) could have been better covered by the conventional approach. Nausea ± vomiting requiring anti-emetics developed in 34/63 (54%) patients. In 24/70 (34%) patients, major constraints violations, mainly involving pancreatic tail and spleen, were observed. CONCLUSION: This extended national cohort of WT patients confirms the excellent locoregional control rate, using modern flank irradiation, even after a long-term follow-up.