Development and evaluation of a thallium (I) bromide dosimeter for intracavitary radiotherapy quality assurance

Abstract

In intracavitary radiotherapy, incorrect source locations can result in excessive doses to normal tissues. Therefore, it is essential to accurately evaluate the source location. In this study, we investigated a digital line dosimeter based on thallium (I) bromide (TlBr) to improve the existing analogue verification method. Therefore, a polycrystalline TlBr unit cell dosimeter was manufactured, and the measurement performance of iridium-192 (Ir-192) sources was evaluated. We found that the dosimeter's reproducibility satisfied the evaluation criteria of 1.5% with a relative standard deviation of 1.44%. Moreover, the linearity showed excellent results (linear coefficient, R 2 = 0.9999). The distance dependence showed a difference of 0.03 cm at 50% intensity when compared to the inverse square value, whereas the angular dependence showed a large difference when compared to a diode. As the angle increased, the intensity gradually decreased, resulting in a difference of up to 41.9%. These results demonstrate the excellent performance of the TlBr dosimeter. However, because of the significant influence of angular dependence, a measurement distance that minimises this error should be applied when manufacturing line dosimeters in the future.

Feasibility study of perovskite film dosimeter for radiotherapy quality assurance

“…The reproducibility evaluation results showed a RSD of 1.058% at 6 MV and 1.003% at 15 MV, which is within 1.5% of the evaluation criteria [17]. The linearity evaluation result was R 2 0.9999 at 6 MV and 15 MV respectively, and R 2 satisfied the evaluation criteria with 0.9990 or higher [7]. The dose rate dependence evaluation showed RSD results of 1.242% and 0.628% at 6 MV and 15 MV, respectively.…”

“…The dose rate dependence evaluation showed RSD results of 1.242% and 0.628% at 6 MV and 15 MV, respectively. This demonstrates a dose rate dependence suitable for application to QA dosimeters [7].…”

“…For linearity evaluation, we obtained a signal while gradually increasing the dose irradiated intensity from 3, 10, 50, 100, 300, 500, to 1000 MU at 500 MU/min. The linearity was evaluated with the coefficient of determination (R 2 ) calculated from linear regression analysis [7]. The closer R 2 is to 1, the better the linearity.…”

“…Dose rate independence was evaluated by gradually examining doses from 1 MU to 1000 MU at each dose rate of 100, 200, 300, 400, 500, and 600 MU/min. The measured signal was normalized based on that for 300 MU, and the RSD for the 100 MU measured values was calculated and evaluated [7]. The PDD was calculated by measuring the dose of the slab phantom at a depth of 1 mm to 250 mm.…”

“…However, when the silicon diode is damaged by radiation, performance degradation such as leakage current, bulk resistance, space charge concentration, and free carrier trapping occurs [2,3]. Consequently, research on developing materials to replace existing semiconductor dosimeters is being conducted [4][5][6][7][8][9][10][11][12][13][14][15][16]. In particular, perovskite is widely used in devices owing to its simple manufacturing process, excellent x-ray detection capability, and excellent thermal safety [8][9][10][11][12][13][14][15][16].…”