Validation of a cost-effective heterogeneous pediatric head phantom for CT-based HU-density calibration in radiotherapy treatment planning: A dosimetric evaluation in pediatric brain tumor cases

This study evaluates the clinical applicability of a novel heterogeneous pediatric head phantom for CT (Computed Tomography)-based Hounsfield Unit (HU)-density calibration in radiotherapy treatment planning. The phantom, made of a customized epoxy resin blend with tissue-equivalent inserts, addresses the limitations of existing phantoms in pediatric applications. The new calibration curve, derived from the pediatric phantom, was compared to the established EasyCube phantom curve in 10 pediatric brain tumor cases who underwent cerebrospinal irradiation (CSI). Treatment plans were generated using the RayStation TPS and dosimetric accuracy was assessed through dose-volume histogram (DVH) analysis and gamma index criteria (3 %/3 mm and 2 %/3 mm). Results showed high gamma index passing rates of 95.7 % (3 %/3 mm) and 93.4 % (2 %/3 mm), confirming the robustness of the new calibration curve. The pediatric phantom-based plans improved organs at risk (OARs) sparing, including the spinal cord, eyes, lenses and kidneys, while maintaining required PTV (Planning Target Volume) coverage (V_95 % = 98 ± 3 %) and dose homogeneity (homogeneity index 0.09 ± 0.010). The new plan achieved slight reductions in D_50 % and D_98 % for PTV CSI and SpinalCord (Thorax), while maintaining D_2 % at ∼37 Gy. For OARs, the right eye showed a minor decrease in D_50 % (13.11 ± 2.59 to 13.04 ± 2.39 Gy), while the left eye and lenses also exhibited mean reduction of ∼0.06 Gy. The kidneys demonstrated nearly identical dose distributions. The new calibration curve kept required dose homogeneity and conformity, with PTV coverage consistently above 90 %, aligning with the International Commission on Radiations Units and measurements (ICRU) recommendations. These findings highlight the clinical utility of the pediatric phantom in improving dose calculation precision for pediatric radiotherapy, offering a cost-effective and accessible solution for low-resource settings. The study highlightsthe importance of age-specific phantoms in optimizing treatment plans and reducing the risk of radiation-induced complications in pediatric patients. Further clinical validation is recommended to confirm the long-term benefits of this approach.