Development and evaluation of polycrystalline semiconductor dosimeter for quality assurance application in high-dose-rate brachytherapy

초록

This study aims to develop and evaluate polycrystalline semiconductor dosimeters (PSDs) to establish a digital quality assurance (QA) system for high-dose-rate (HDR) brachytherapy. PSDs were fabricated using four polycrystalline materials: mercury(II) iodide (HgI2), lead(II) iodide (PbI2), lead(II) oxide (PbO), and thallium(I) bromide (TlBr). To evaluate the performance of the fabricated dosimeters, dosimetric parameters, including reproducibility, dose-response linearity, distance dependence, and angular dependence, were measured using an Iridium-192 (Ir-192) radioisotope source and compared with corresponding parameters measured by a parallel-plane ionization chamber. For reproducibility, each PSD was irradiated 10 consecutive times. Dose-response linearity was assessed for doses ranging from 0.1 to 10 Gy. Distance dependence was evaluated by administering a dose of 1 Gy at source-to-dosimeter distances ranging from 1 to 12 cm, in increments of 0.25 cm. Angular dependence was assessed by positioning the PSDs 1 cm below the Ir-192 source and measuring signals at angles of 15 degrees, 30 degrees, and 45 degrees relative to the reference angle of 0 degrees, where the PSD's central axis was parallel to the source. Signals measured at 15 degrees, 30 degrees, and 45 degrees were normalized to those measured at 0 degrees. The PSD using PbO demonstrated the best reproducibility, with a coefficient of variation of 0.85%, and showed a minimal difference of-0.03% compared with the ionization chamber. Other PSDs also achieved excellent reproducibility, with relative standard deviations within 1.5%. For dose-response linearity, all PSDs achieved an R2 value of 0.9993 or higher, outperforming the ionization chamber, which had an R2 value of 0.9983. Regarding distance dependence, the slope of the power function and the distance corresponding to 50% intensity (D50) were analyzed in comparison with the ionization chamber. The PSD using PbI2 exhibited the closest agreement, with a slope difference of 0.103 and a difference of 0.003 cm for D50. For angular dependence, the PSD using PbI2 demonstrated the least attenuation, with a redcution of 13.2% in signal intensity at 45 degrees compared with 0 degrees. The findings of this study indicated that PbI2 was the most suitable material for PSDs by comparing with the ionization chamber in terms of measurement characteristics. Furthermore, this study provided valuable insights into optimizing semiconductor materials for various applications in HDR brachytherapy QA.

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