Speaker
Description
High-dose-rate (HDR) brachytherapy using Iridium-192 (Ir-192) sources is widely adopted in the treatment of various cancers due to its ability to deliver concentrated radiation doses with high spatial precision. Accurate dose verification is essential in this modality to ensure both treatment efficacy and patient safety. In this study, we investigate the feasibility and performance of polycrystalline semiconductor dosimeters (PSDs) fabricated with lead (Ⅱ) iodide (PbI₂) and lead oxide (PbO) materials for use in HDR brachytherapy dosimetry. Specifically, we evaluated the distance and angular dependence of these PSDs when exposed to an Ir-192 source, and validated the results through comprehensive Monte Carlo (MC) simulations using the GATE v9.1 toolkit.
The PbI₂ and PbO materials were fabricated with dimensions of 0.2 cm x 0.2 cm through a polymer mixture, and gold electrodes were formed to construct the detector. Experimental measurements were performed to assess the PSDs’ responses at source-to-surface distances (SSD) ranging from 1 cm to 8 cm and at incident angles from 0° to 60°. In parallel, MC simulations replicated these conditions to model radiation interactions and validate the experimental results.
For distance dependence, both PSD types showed signal attenuation consistent with the inverse-square law, with power-law exponents of approximately -1.9 for PbI₂ and -1.8 for PbO, in both measurements and simulations. High coefficients of determination (R² > 0.98) confirmed the strong correlation between distance and signal intensity. Additionally, the D50 values, representing the distance at which the normalized signal dropped by 50%, were closely matched between measurement and simulation, with discrepancies less than 0.01 cm for both PSD types. In evaluating angular dependence, both PSDs demonstrated a gradual decline in normalized signal intensity as the irradiation angle increased. The maximum signal reduction at 60° was approximately 25%, indicating significant angular sensitivity. The difference between experimental and simulation data remained within 5% for all angles, with the PbI₂-based PSD exhibiting slightly better agreement than the PbO counterpart. These findings highlight the reproducibility and reliability of the fabricated PSDs and their potential for accurate dosimetry. The use of PbI₂ and PbO as photoconductive materials is particularly promising due to their high atomic numbers and favorable charge transport properties, contributing to efficient photon absorption and stable signal generation. This study is among the first to report on the fabrication of PbI₂ and PbO-based PSDs and their comprehensive characterization under HDR Ir-192 irradiation through both experimental and simulated approaches. Compared to prior works that utilized TlBr or CsPbBr₃ without simulation validation, our dual-method approach enhances confidence in the clinical applicability of these PSDs.
In conclusion, PbI₂ and PbO-based PSDs demonstrated reliable and predictable responses to Ir-192 irradiation in both distance and angular dependence measurements. The consistency with MC simulations supports the robustness of the fabrication and evaluation methodology. However, the observed angular sensitivity suggests that implementing angular correction factors would be necessary for clinical dosimetry applications. Future studies should focus on optimizing the PSD design for real-time monitoring and incorporating correction algorithms to enhance accuracy in complex treatment geometries.
| Workshop topics | Sensor materials, device processing & technologies |
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