Study on the feasibility of the HgI2 dosimeter for quality assurance of radiotherapy

In radiotherapy, a variety of detectors such as ionization chambers, films, TLDs, diodes, and OSL, are being used for quality assurance (QA). Owing to its high sensitivity and feasibility to operate at low voltages, silicon (Si) photoconductors, which are used as detection material of a diode, are currently being used as relative dosimeters. In addition, other materials such as amorphous selenium (a-Se), cadmium telluride (CdTe), lead iodide (PbI2), and mercury iodide (HgI2) were also being investigated for their feasibility as diagnostic radiation detector. Among these materials, HgI2 has been reported to show remarkable properties including high spatial resolution and high stopping power. Hence In this study, we have verified the feasibility of HgI2 dosimeter for quality assurance of radiotherapy. In order to fabricate the detector, HgI2 was mixed with TiO2 to minimize the signal reduction. Following this, the resulting mixture was deposited onto indium tin oxide (ITO) coated glass by particle-in binder (PIB) method. Finally, the top ITO electrode was coated by magnetron sputterring system. Subsequently, we measured the electrical properties generated by high-energy radiation from linear accelerator (LINAC), and analyzed the reproducibility, linearity, and percent depth dose (PDD) of the fabricated detoctor. In addition, we have determined the build-up materials in experimental setup, since the thickness of build-up region, where the secondary electron emission equilibrium occurs, changes depending on radiation energy. It was observed that the relative variations measured as standard deviation divided by the average value among repeated measurements was approximately 1%. Deviations from linearity are smaller than 5%. Finally, we compared the experimental data of the detector fabricated in this study with those of the farmer-type ionization chamber. Base on the results obtained from this study, it could be realized that HgI2 could be used as dosimeter for QA of radiotherapy.