Estimation of detailed cardiac doses for pediatric radiotherapy patients in National Wilms Tumor Study.

Abstract

Substructure-level heart dosimetry may improve the evaluation of long-term cardiac toxicity in childhood cancer survivors, but detailed pediatric heart models are limited. We developed age-specific heart models (1, 5, 10, and 15 years) using high-resolution imaging and integrated them into computational phantoms to estimate cardiac substructure doses in patients treated on the National Wilms Tumor Study (NWTS) protocols and evaluate the impact of anatomical detail on radiotherapy dose estimates. Heart models with detailed substructures including chambers, myocardium, arteries, valves, and conduction nodes were developed from pediatric MR and adult CT images. These were incorporated into a size-dependent phantom library representing a wide range of pediatric body sizes. Patient-specific radiotherapy plans were reconstructed using the Pinnacle treatment planning system, and heart doses were calculated using both treatment planning system (TPS) and Monte Carlo (MC) methods. The developed heart models closely matched ICRP reference masses (within 2%). TPS and MC dose calculations showed strong agreement (median difference <2%) so that MC-based doses were used for further analysis. Among 4,716 NWTS patients treated with radiotherapy, the median whole-heart dose was 4.2 Gy. Cardiac and substructure doses varied by treatment region with the right atrium and left ventricular myocardium receiving higher doses (up to 5.1 and 4.5 Gy), while coronary arteries and valves received lower doses (<1 Gy). In non-chest fields, substructure doses differed significantly from whole-heart doses (p < 0.001), reflecting steep intra-cardiac dose gradients. Chest fields alone resulted in uniformly high cardiac doses with minimal variation. Our results demonstrate that relying solely on whole heart dose may obscure clinically relevant exposure to critical substructures. Detailed heart models enable more accurate dosimetry and support improved risk assessment and safer pediatric radiotherapy planning to reduce long-term cardiac toxicity.