The feasibility Assessment of the Dynamic Prosthesis Treatment Planning Dose Verification of NIPAM Gel Dosimeter

• Main Authors: Cheng, Chih-Wu, 鄭智武
• Other Authors: Hsieh, Bor-Tsung
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/69139100354022172984

碩士 === 中臺科技大學 === 醫學影像暨放射科學系暨研究所 === 103 === Purpose：Evaluation of NIPAM gel dosimeter under respiratory motion to verify radiotherapy treatment plan. Materials and Methods：We used a self-designed NIPAM gel dosimeter and a set of NIPAM gel calibration tubes to perform the experiment. The calibration tubes and gel dosimeter were set on a movable device which simulated respiratory movement of the chest. The movement parameters of the calibration tubes and the gel dosimeter were: ±10mm cephalic and caudal displacement (20mm in total), and a period of 4 seconds. Correction and gel dosimeter before irradiation CT images were taken by CT simulator. The calibration tube was made by filling NIPAM gel into a test tube. For each calibration tube, a specific radiation dose of 0,1, 2, 5, 8,10Gy (6MV photon) was given respectively by a Varian iX Linear accelerator. MRI scan was then performed to each calibration tube after irradiation and the T2 value obtained was converted to R2 value before a calibration curve was plotted. Another cylinder was also filled with NIPAM gel. A treatment plan of bilateral tangential forward field-in-field IMRT was done by Varian Eclipse planning system. The gel dosimeter was then irradiated up to 5.4Gy (6MV photon) with Varian iX linear accelerator using the treatment plan generated by the treatment planning system. A MRI scan was then performed, and the image data was than analyzed with MATLAB to evaluate dose curve change between the treatment plan and the gel dosimeter. Results：The sensitivity of the calibration gel dosimeter was 0.1353 s-1/Gy. The correlation coefficient (R2) of the calibration curve was 0.9952. In axial sections, when comparing dose distribution of the treatment plan and the gel dosimeter, 70% and 80% isodose curves were in high concordance. In sagittal and coronal views, the area of low dose region (<60% isodose curves) in the gel dosimeter was larger than that of the treatment plan. In addition, the area of high dose region in the treatment plan was larger than that of the gel dosimeter. Conclusion：We demonstrated three-dimensional dose distribution of the NIPAM gel dosimeter with respiratory motion, had high concordance with that of the calculated treatment plan. Therefore using NIPAM gel dosimeter to verify radiotherapy treatment plan with respiratory motion is feasible.