Evaluation of distance and angular dependence of polycrystalline semiconductor dosimeters for Ir-192 brachytherapy source using experimental measurements and Monte Carlo simulations

초록

Background: This study evaluates the distance and angular dependence of polycrystalline semiconductor-based dosimeters (PSDs) using lead (II) iodide (PbI 2) (PbI2 PSD) and lead (II) oxide (PbO) (PbO PSD) for Ir-192 brachytherapy source. Experimental measurements were compared with Monte Carlo (MC) simulations to verify the dosimeters' performance and accuracy. Materials and Methods: PSDs were fabricated using PbI2 and PbO as photoconductive materials, with a thin-film deposition process ensuring uniformity. Distance dependence was assessed by measuring dosimeter responses at source-to-surface distances ranging from 1 cm to 8 cm at 0.25 cm intervals, while angular dependence was evaluated at angles from 0 degrees to 60 degrees in 15 degrees increments. MC simulations using the Geant4 Application for Tomographic Emission (GATE) v9.1 were conducted under identical conditions to validate the experimental measurements. Results: The experimental and simulated data demonstrated a strong agreement with the inverse-square law, with determination coefficient (R-2) exceeding 0.98 for PbI2 and PbO PSDs. The distance at which the signal intensity dropped by 50% (D50) for measurements and simulations was 1.493 cm and 1.487 cm for PbI2 PSD, respectively, and 1.488 cm and 1.481 cm for PbO PSD. Angular dependence analysis showed a decrease in response with increasing angle, with PbO PSD exhibiting slightly larger discrepancies (maximum difference of 5.48%) compared to PbI2 PSD (maximum difference of 4.56%) between measurements and simulations. Conclusion: PbI2 and PbO PSDs demonstrated predictable distance and angular dependence, closely aligning with MC simulations. However, angular correction factors may be necessary to improve dosimetric accuracy in clinical applications.

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