Study of secondary neutron and γ dose distribution based on a TLD array and 3D-printed tissue-equivalent phantom.

Abstract

Secondary neutron and gamma radiation in proton therapy raise concerns regarding out-of-field doses and heightened risks of secondary malignancies, particularly in pediatric cases. This study aims to develop and validate a novel 3-dimensional (3D) printed, tissue-equivalent phantom designed to enhance the precision of absorbed dose measurements and improve treatment planning in proton therapy. The phantom was fabricated using advanced 3D printing technology to mimic the radiological properties of human tissues, including electron density and proton stopping power. Thermoluminescent detectors (TLDs) were embedded at designated locations to measure doses resulting from proton irradiation. The γ-ray dose distribution inside the phantom was verified by comparison with Monte Carlo simulations using the GATE toolkit to ensure consistency and reliability. Measured dose distributions demonstrated strong consistency with simulations. Within the treatment field, the dose distribution exhibited high precision, while secondary doses featured a sharp decline beyond 6 cm from the target center. Doses fell below 5 mSv/Gy(RBE) within 1 cm of the boundary and continued to taper off to 0.05∼0.15 mSv/Gy(RBE) further away. Neutron dose equivalents were recorded at less than 1.5 mSv/Gy(RBE) between 5∼10 cm, declining below 1.0 mSv/Gy(RBE) beyond 10 cm. The 3D-printed phantom demonstrated high reliability and accuracy in dosimetry. It represents a robust tool for quality assurance in proton therapy planning and for evaluating patient-specific out-of-field doses. The model is expected to improve the safety and efficacy of radiation therapy, addressing critical concerns relevant to vulnerable populations. Furthermore, the measured out-of-field neutron doses were compared with the results from published studies to verify the rationality of the experimental data, which could provide a reference for the secondary neutron risk assessment of low-energy proton radiotherapy.