放射治療劑量分布驗證之研究：探討凝膠劑量計照射後最佳量測時間

Study of Dose Distribution Verification for Radiation Therapy: Optimal Readout Time of Imaging Modalities for Post-irradiated Gel Dosimeters

施煥達(Hsau-Dar Shy) ； 黃琮傑(Tsung-Chieh Huang) ； 史天宇(Tian-Yu Shih) ； 謝玲鈴(Ling-Ling Hsieh)

《臺灣醫事放射期刊》 6卷2期 (2018/12) Pp. 8-16

https://doi.org/10.6717/JTMRT.201812_6(2).0002

摘要

本研究以NIPAM (N-isopropyl acrylamide)凝膠劑量計為研究對象，搭配磁振造影(magnetic resonance imaging, MRI)作為凝膠劑量計的測量工具，並運用凝膠的遲豫率R_2(= 1/T2 )值與照射劑量關係、三個切面等劑量曲線圖及伽馬評估等方法探討小體積與大體積凝膠劑量計經照射後輻射訊號最佳量測時間。研究數據顯示小體積劑量計照射後2小時即可達到很好的線性度，敏感度則隨時間會些許增加，線性相關係數(2~168小時)約為0.9989到0.9997的範圍，具有很好的線性關係且照射後12小時開始凝膠敏感度及線性關係趨近最佳值。另外，以臨床治療計畫照射大體積的凝膠假體，比較治療計畫與凝膠量測所得三個切面最接近腫瘤中心（靶中心）位置的水平切面、冠狀切面和矢狀切面分析出照射後的劑量分布，隨時間變化仍然有非常高的穩定度，兩者的曲線具有高吻合度。以距離一致性為3mm，劑量通過率3%條件下進行伽馬評估，本研究發現突破性結果，凝膠劑量計於照射後12小時，劑量通過率可高達95%以上。因此，以MRI作為凝膠劑量計量化計讀的測量工具，可提前於照射後12小時進行訊號量測，縮短照射後凝膠至訊號量測時間，提升凝膠劑量計之實用性。

關鍵字

聚合物凝膠劑量計 ； NIPAM ； 等劑量曲線 ； 伽馬評估

並列摘要

In this study, dose calibration curves, dose distributions, and gamma evaluation were utilized to investigate the optimal readout time of various post-irradiated sizes by using N-isopropyl acrylamide (NIPAM) gel dosimeters with magnetic resonance imaging (MRI). The results of the current experiment demonstrated that good linearity could be achieved 2 h after irradiation with a small volume of gel and that sensitivity increased slightly with time with high linear correlation coefficients of approximately 0.9989-0.9997 (2~168 h). Gel sensitivity and linearity approached optimal values 12 h after irradiation. Large-volume gel phantoms were irradiated by intensity-modulated radiation therapy (IMRT), and the dose distributions measured in the axial, coronal, and sagittal directions were compared with those calculated using a treatment planning system. Results showed that the dose distributions were highly stable over time, and good agreement among all selected planes was obtained. The passing rate of 3 mm and 3% polymer gel dosimetry exceeded 95%, thereby indicating that the large-volume gel phantoms have high accuracy and spatial stability. Taken together, the results demonstrate that NIPAM gel dosimeters with MR readouts could accurately provide the entire dose volume after a 12 h reaction time. NIPAM gel dosimeters with MR readouts could be useful and convenient in dose verification of clinical IMRT.

並列關鍵字

polymer gel dosimeter ； NIPAM ； dose distribution ； polymer gel dosimeter