ESTRO 2022 - Abstract Book

S1369

Abstract book

ESTRO 2022

PO-1588 Dosimetric Characteristics of Photoconductive Material for High Energy Beam in Radiation Therapy

K.B. Kim 1 , G. Cho 2 , K. Kim 2 , S.H. Choi 2

1 Korea Institute of Radiological & Medical Sciences, Department of Radiation Oncology, Seoul, Korea Republic of; 2 Korea Institute of Radiological & Medical Sciences, Research Team of Radiological Physics & Engineering, Seoul, Korea Republic of Purpose or Objective To evaluate the dosimetry characteristics of photoconductive materials for high energy beam in radiation therapy, we fabricated detector unit-cell using the material such as HgI 2 (Mercuric Iodide), HgI 2 -TiO 2 (Mercuric Iodide–Titanium Oxide), PbO (Lead Oxide), PbI 2 (Lead Iodide) and HgO (Mercuric Oxide) by Particle-In-Binder method. Materials and Methods To evaluate the fabricated unit-cells, we measured the dosimetric characteristics that the radiation detector should have such as a high energy response, dose rate dependence, linearity, and reproducibility using 4 and 10 MV photon beam. The radiation field size and source-to-surface distance was 10x10 cm 2 and 100 cm, respectively. The unit-cells were placed in a dark room to make it only respond to the radiation because it has light sensitive property. To obtain output signals of the unit-cells, we use a current to voltage converter circuit because an initial output of the fabricated unit cell is the current. Then, the output signal with voltage was processed by NI DAQ (NI SCB-68). Also, the output signals of the LINAC (Linear Accelerator) beam pulse was obtained by NI DAQ (NI USB-6363) [Figure 1].

Figure 1 Schematic diagram of (a) measurement set-up and (b) signal acquisition circuit

Results As a result, HgI 2 and HgI 2 -TiO 2 cell shows a good response with 1.2, 2.5 and 1.4, 2.6 voltages at the 4 and 10 MV, respectively. Especially, the sensitivity of the HgI 2 unit-cell was higher than that of LINAC output at 10 MV. However, the PbO and PbI 2 unit-cell shows a poor response less than 0.1 voltage. Therefore, further measurement was done using the HgI 2 and HgI 2 - TiO 2 unit cell. The linearity measurement shows that R 2 value is 0.9999 (HgI 2 -TiO 2 ) and 0.9998 (HgI 2 ) at 10 MV. To evaluate the dose rate dependency, the result compared with the LINAC output. The results shows that the HgI 2 unit cell was almost same with the LINAC output as 0.0154 of the RMSE. The reproducibility of the HgI 2 and HgI 2 -TiO 2 unit cell was also compared with the LINAC beam pulse. All the RMSE value shows almost 0. And the standard deviation of the HgI 2 and HgI 2 -TiO 2 unit cell was 0.45% and 0.6% at the 4 MV beam and 0.95% and 0.48% at the 10 MV beam, respectively [Figure 2].