Abstract
Polymer gels are three-dimensional dosimetric tools. The purpose of the present study was to investigate the temperature dependence of polymer gels during scanning Magnetic Resonance Imaging. Prepared gels were irradiated with a 6MV X-ray beam at intensities ranging from 0 to 20 Gy in order to investigate their dose-R2 and dose-R1 responses. Irradiated gels were evaluated from 1.5-T magnetic resonance R2 and R1 images for each 5°C change in temperature from 5°C to 41°C, and then the four-field box technique irradiation plan was used to deliver a total dose of 4 Gy using the same beam weight in each direction to the prepared gels. The profile of the dose map generated from the four-field irradiated gel data at 20°C was then compared with the planned data. The dose-R2 response curve was linear up to 20 Gy at 20°C, with a slope of 1.17 Gy-1˙s-1. The slopes of the fitted curves of the dose-R2 decreased as gel temperature increased. The slopes of the dose-R1 curves were more parallel than the slopes of the dose-R2 curves between 5 and 41°C. The difference in the full width of half maximum of the gel profile data obtained using the four-field box technique at 20°C and the planned data were below 5% on average. The dose map from the irradiated gels obtained using the dose-R2 curve was the same as that from the planned data under the same temperature conditions. Measurement of difference between various temperatures is significant with dose accuracy. It is suitable to evaluate the gel dosimeter under the thermal equilibrium condition, MRI room temperature from the point of view of the stability of the irradiated gels.
Highlights
Polymer gels provide new three-dimensional (3D) dosimetric tools that hold promise for the 3D measurement of 3D doses during clinical radiotherapy, enhancing quality assurance
The fitted straight line for photon dosimetry at 20 ̊C had a gradient of 1.17 Gy−1∙s−1 and an intercept of 3.87 s−1, and the coefficient of correlation was 0.998
This study revealed the temperature dependency of polymer gel dosimeters during scanning Magnetic Resonance Imaging (MRI)
Summary
Polymer gels provide new three-dimensional (3D) dosimetric tools that hold promise for the 3D measurement of 3D doses during clinical radiotherapy, enhancing quality assurance. Measurements using an ion chambers are precise, but an ion chamber is a point-detector, and is not suited to 3D dosimetry. The clinical use of current polymer gel dosimeters faces several problems, including the temperature stability of polymer gels under irradiation and during dosimetric evaluation using Magnetic Resonance Imaging (MRI). Polymer gel dosimetry evaluated using MRI is conducted in low temperature environments because the gels melt at temperatures over approximately 25 ̊C, providing poor spatial information and inaccurate dosimetric results. Precise measurements of polymer gels in clinical settings are needed in order to determine the temperature dependence of polymer gels
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