| Summary: | 碩士 === 中國醫藥大學 === 生物醫學影像暨放射科學學系碩士班 === 104 === In current study, dose characteristics and verification of both brachytherapy and external beam radiotherapy was compared by using N-isopropylacrylamide (NIPAM) gel dosimeter and optical computed tomography (optical-CT).
NIPAM polymer gel dosimeter was adopted to record three-dimensional (3D) dose distribution. A CCD-based parallel-beam optical-CT scanner developed by ourselves to perform dose measurement. The gamma evaluation technique was used to calculate the pass rate by comparing the measured data and TPS point by point. The criteria is 3% dose-difference (DD) and 3 mm dose-to-agreement (DTA).
For external beam radiotherapy, two different kinds of cancer cases were chosen including a simple lung cancer and a more complex larynx cancer. In addition, two radiation techniques were used to generate the TPS including intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) with Elekta accelerator (Elekta Axesse™, Sweden).
The result show that NIPAM polymer gel dosimeter showed good agreement for simple lung cancer TPS and for complex larynx cancer TPS. For a complex larynx cancer TPS, although VMAT can provides more conformal dose irradiation than IMRT, the gel dosimeter seems show disagreement in high dose gradient region where high dose rate irradiation was issued.
For high dose rate brachytherapy, the NIPAM gel phantom with horizontal plastic source catheter was irradiated by using Nucletron micro-Selectron with radiation source Ir-192. The results showed that the dose measured at 2 cm from seed center showed good agreement for HDR brachytherapy. However, the refraction and scattering caused by source catheter affected the dose distribution measured by gel dosimeter. Therefore, the measured dose distribution showed disagreement near the seed center. Besides, streak artifact was observed during image reconstruction and it needed to improve in the future study.
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