Post-operative flank irradiation using conformal versus highly conformal radiotherapy techniques for paediatric renal tumours: Results from the French registry PediaRT.

PURPOSE: Three-dimensional conformal RT (3D-RT) techniques are gold standard for post-operative flank radiotherapy (RT) in paediatric renal tumours. Recently, highly conformal RT (HC-RT) techniques have been implemented without comparative clinical data. The main objective of this multicentre study was to compare locoregional control (LRC) in children treated either with HC-RT or 3D-RT techniques. METHODS: Patients treated with post-operative flank RT for renal tumour registered in the national cohort PediaRT between March 2013 and September 2019 were included. Treatment and follow-up data, including toxicities and outcomes, were retrieved from the database. LRC was calculated, and dose reconstruction was performed in case of an event. RESULTS: Seventy-nine patients were included. Forty patients were treated with HC-RT and 39 with 3D-RT. Median follow-up was 4.5 years. Three patients had locoregional failure (LRF; 4%). HC-RT was not associated with a higher risk of LRF. Three-year LRC were 97.4% and 94.7% in the HC-RT and 3D-RT groups, respectively. The proportion of planning target volumes receiving 95% or more of the prescribed dose did not significantly differ between both groups (HC-RT 88%; 3D-RT 69%; p = .05). HC-RT was better achieving dose constraints, and a significant mean dose reduction was observed in the peritoneal cavity and pancreas associated with lower incidence of acute gastrointestinal toxicity. CONCLUSION: LRF after post-operative flank RT for renal tumours was rare and did not increase using HC-RT versus 3D-RT techniques. Dose to the pancreas and the peritoneal cavity, as well as acute toxicity, were reduced with HC-RT compared to 3D-RT.