Author: Woong Cho, Jin-Beom Chung, Moo-Jae Han, Sang Won Kang, Boram Lee 👨🔬
Affiliation: Department of Radiation Oncology, Seoul National University Boramae Medical Center, Department of Radiation Oncology, Seoul National University Bundang Hospital, Department of Radiation Oncology, Inha University Hospital 🌍
Purpose: This study aims to establish a digital quality assurance (QA) system for high-dose-rate (HDR) brachytherapy by evaluating self-developed polycrystalline semiconductor dosimeters (PSDs).
Methods: PSDs were fabricated using four polycrystalline materials: mercury(II) iodide (HgI₂), lead(II) iodide (PbI₂), lead(II) oxide (PbO), and thallium(I) bromide (TlBr). Their dosimetric performance was assessed based on reproducibility, dose-response linearity, distance dependence, and angular dependence, using an Ir-192 source. Measured dosimetric parameters were compared to those from a parallel-plane ion chamber. Reproducibility was tested by irradiating each PSD 10 times consecutively. Dose-response linearity was evaluated for doses from 0.1 to 10 Gy. Distance dependence was measured at source-to-dosimeter distances of 1 to 12 cm, in 0.25 cm increments for a 1 Gy dose. Angular dependence was assessed by placing the PSDs 1 cm below the source and normalizing measured signals at angles of 15°, 30°, and 45° relative to the signal at 0° as a reference.
Results: The PbO-based PSD demonstrated the best reproducibility, with a coefficient of variation of 0.85% and a minimal difference of -0.03% compared to the ion chamber. Other PSDs also exhibited 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 chamber’s R² value of 0.9983. In distance dependence, PbI₂-based PSD showed the closest agreement with the ion chamber, with a slope difference of 0.103 and a the distance of 50% intensity (D₅₀) difference of 0.003 cm. PbI₂-based PSD also had the least angular attenuation, with a 13.2% reduction in signal intensity at 45° compared to 0°.
Conclusion: PbI₂ was identified as the most suitable material for PSD when compared to ion chamber in terms of measurement characteristics. This study provides valuable insights into optimizing polycrystalline materials for various PSDs in HDR brachytherapy QA.