應用NIPAM凝膠劑量計在呼吸運動下驗證放射治療計畫的可行性研究

ApplicAtion of nipAM gel dosiMeter to verify rAdiotherApy treAtMent plAn in siMulAted breAthing Motion: A feAsibility study

鄭智武(Chih-Wu Cheng) ； 謝栢滄(Bor-Tsung Hsieh) ； 曾玉華(Yuk-Wah Tsang) ； 孫榮章(Jung-Chang Sun) ； 張志嘉(Chih-Chia Chang) ； 謝志明(Chih-Ming Hsieh) ； 林秉津(Ping-Chin Lin) ； 梁恆(Joseph Hang Leung)

《放射治療與腫瘤學》 22卷4期 (2015/12) Pp. 297-306

https://doi.org/10.6316/TRO/201522(4)297

摘要

目的：利用NIPAM凝膠劑量計進行呼吸情況下放射治療計畫劑量驗證的可行性評估。材料與方法：本實驗使用校正試管和凝膠劑量計分別設置於自行設計的模擬胸部呼吸運動的可移動設備上進行實驗。校正管和凝膠劑量計的運動參數為：±1 cm頭腳向位移（總長2 cm），每4秒來回一次。照射前校正管和凝膠劑量計經由CT simulator取的CT影像，由Varian的Eclipse計劃系統完成治療計畫及計算MU值。NIPAM凝膠校正管為一玻璃試管，使用Varian iX直線加速器照射，照射劑量分別為0、1、2、5、8、10 Gy（6 MV光子）。然後進行MRI掃描，取得每個校正管照射後所獲得MRI的T2值並將其轉換為R2值，繪製劑量校正曲線。另外，將圓柱型空瓶內填充NIPAM凝膠，使用Varian iX直線加速器執行bilateral tangential forward field-infieldIMRT治療計畫，照射劑量5.4 Gy（6 MV光子）。然後進行MRI掃描，使用MATLAB軟件進行分析比較，評估治療計畫和凝膠劑量計的劑量曲線的變化。結果：校正結果靈敏度為 0.1353 s-1/Gy，劑量曲線的相關係數（correlation coefficient, R2）為0.9952。軸向切面比較治療計劃和凝膠劑量計的劑量分佈，在70%至80%的劑量曲線有較高吻合度。矢狀面和冠狀面治療計畫和凝膠劑量計的低劑量區（＜ 60%劑量曲線）其劑量曲線面積大於治療計畫面積。此外，高劑量的區域中的治計療計劃的面積比凝膠劑量劑量曲線面積大。結論：本模凝實驗證明了NIPAM凝膠劑量計搭配可移動設備所取得三維劑量分佈變化與治療計畫計算值是一致，因此使用NIPAM凝膠劑量計來驗證呼吸情況下的放射治療計劃是可行的。

關鍵字

三維劑量分佈 ； 劑量驗證 ； NIPAM凝膠劑量計 ； 劑量曲線

並列摘要

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: ±10 mm cephalic and caudal displacement (20 mm 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, 8,10 Gy (6 MV 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 5.4 Gy (6 MV 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 (R^2) 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.

並列關鍵字

Three-dimensional dose distribution ； Dose verification ； NIPAM gel dosimeters ； Dose curve