The Effect of MRI Parameters on the Sensitivity and Dose Resolution of PASSAG Polymer Gel Dosimeter

Magnetic resonance imaging (MRI) system is used as one of the most common methods to read out the response of polymer gel dosimeters. The imaging protocols can have a remarkable effect on the response of polymer gel dosimeters; hence, the impact of imaging parameters on the response of each type of polymer gel dosimeter should be addressed. This study aims to investigate the effect of MRI parameters on PASSAG polymer gel dosimeter response. PASSAG gel dosimeter was first fabricated and then, these gel samples were irradiated by a 6 MV X-rays. Thereafter, the MRI responses (R2) of the gel samples were analyzed. In addition, the impact of MRI parameters, including number of echoes (NOE), echo spacing (ES), repetition time (TR), and matrix size, on the sensitivity and dose resolution of the gel samples were evaluated. The findings showed that the highest R2–dose sensitivity belongs to the gel samples imaged with 32 NOE. It was also found that the dose resolution value improves with the increase of NOE. The R2–dose sensitivities and dose resolution values obtained from PASSAG gel samples imaged with ESs of 16.8, 22.0, and 27.2 ms were almost the same. Furthermore, the R2–dose sensitivities of gel vials imaged with TRs of 2000, 4000, and 6000 ms are almost the same (a 0.00–0.80% difference range), while the R2–dose sensitivity of gel vials imaged with 8000 ms was remarkably different from the sensitivities of gel vials imaged with other TRs (a 7.85–8.65% difference range). In addition, the dose resolution values of PASSAG gel dosimeter are almost the same for the evaluated TRs. There was a 0.80–11.58% difference range between the R2–dose sensitivities of gel vials at different matrix sizes, as these findings represent that the R2–dose sensitivity of PASSAG gel dosimeter is dependent on the matrix size. In addition, the dose resolution values of PASSAG gel dosimeter vary over the matrix size. According to the obtained results, it can be concluded that the TR and matrix size affect the response (R2–dose sensitivity and dose resolution) of PASSAG gel dosimeter more than the NOE and ES.