使用電子影像驗證裝置在弧形強度調控放射治療的驗證

Dosimetry Verification of RapidArc Volumetric Modulated Arc Therapy with Electronic Portal Imaging Device

李秉倫(Pin-Lun Li) ； 鄭梅君(Mei-Chun Cheng) ； 趙良曉(Liang-Hsiao Chao) ； 劉晉昇(Ching-Sheng Liu) ； 劉雪君(Shueh C. Liou) ； 李玉麟(Yuh-Lin Lee) ； 劉裕明(Yu-Ming Liu) ； 王令瑋(Ling-Wei Wang) ； 顏上惠(Sang-Hue Yen) ； 黃英強(David Y. C. Huang) ； 陳信雄(Hsin-Hsiung Chen) ； 趙敏(Max M. Chao)

《放射治療與腫瘤學》 20卷1期 (2013/03) Pp. 49-56

https://doi.org/10.6316/TRO/201320(1)49

摘要

目的：使用電子影像驗證裝置（EPID, VARIAN aS-1000）設備，配合 Epiqa 劑量驗證軟體來驗證弧形強度調控治療計畫的劑量分布。材料與方法：Epiqa是一套基於GLAaS理論將電子影像驗證裝置影像轉換成劑量圖（dose map）的軟體，可用來驗證弧形強度調控（RapidArc）放射治療。將劑量影像轉換為劑量圖，必需透過校正的程序取得不同大小開放照野及穿透照野（transmission field）的影像，並輸入使用游離腔測量的輸出因子係數表；建立電子影像驗證裝置每一個像素（pixel）的校正因子，將像素的讀值轉換為在水中dmax深處的劑量。透過這樣的轉換，可以將電子影像驗證裝置的所有像素轉換成在水中dmax深度處的平面劑量分布圖；便可將治療計畫與電子影像驗證裝置兩者劑量分布比對進而與之驗證。本研究針對20位弧形強度調控放射治療案例進行劑量驗證，其中有7 位攝護腺癌、2位乳癌、3位直腸癌、4位鼻咽癌與4位其它部位。結果：電子影像驗證裝置劑量參數的加馬值（Gamma Agreement Index, GAI）設定吻合距離（DTA）為3毫米，劑量差異（ΔD）3%下，病患的平均GAI[%] 為94.32±3.19（99.06-81.31），而攝護腺癌、乳癌、直腸癌、鼻咽癌與其它部位的平均GAI[%]分別為93.62±4.03（99.06-81.31）、97.43±1.14（98.86-96.24）、92.96±2.51（97.19-89.01）、94.98±2.31（97.64-89.09） 與94.95±2.48（98.9-90.76），乳癌的GAI[%]呈現較好的結果（最低值達到96.24），其中攝護腺癌的1位患者在3個Arc中，有2個Arc的GAI[%]值在90%以下。結論：利用Epiqa這套軟體驗證治療計畫運算所得的劑量，作為劑量驗證的工具是一種簡單且可行的的方法，希望累積更多臨床的驗證資料，使未來劑量驗證的程序更加理想。

關鍵字

電子影像驗證裝置 ； 加馬吻合指數 ； 弧形強度調控放射治療 ； 劑量驗證

並列摘要

Purpose: Verification of dose distributions for RapidArc Volumetric Modulated Arc Therapy (VMAT) treatment plans with Electronic Portal Imaging Device (EPID) and its associated software.Materials and Methods: Epiqa is software to covert the EPID images into dose map based on the GLAaS theory. It can be used to verify the dose distributions for RapidArc therapy. To convert images into dose map, we need to have calibration factors for each pixel to covert the pixel values into dmax dose in water. For the purpose of calibration, a set of integrated images for open and transmission fields of different field sizes are acquired and consequently imported into Epiqa together with the output factor table to establish basic algorithm configuration data. A calibration factor can then be determined for every pixel of EPID images by weighting the contribution of primary and transmitted radiation. The pixel based calibration relates the readout of a pixel to a dose at the depth of dmax in water equivalent homogenous medium. By applying the conversion factors to all pixels of the EPID images, a planar dose distribution at the dmax in water is obtained. A total of 20 patients (70 arcs in total) were included in this study, 7 with prostate cancers, 2 with breast cancer, 4 with rectal cancer, 4 with NPC, and 4 with other sites.Results : The Distance to Agreement (DTA) and the Dose Difference (ΔD) for The Gamma Agreement Index (GAI) of dosimetry parameters with EPID were set as 3 mm and less than 3% respectively. The average GAI (%) of patients in our study is 94.32 ± 3.19 (99.06-81.31). GAI (%) for prostate cancer, breast cancer, rectal cancer, NPC, and other sites is 93.62 ± 4.03 (99.06-81.31), 97.43 ± 1.14 (98.86-96.24), 92.96 ± 2.51 (97.19-89.01), 94.98 ± 2.31 (97.64-89.09), and 94.95 ± 2.48 (98.9-90.76), respectively. The GAI (%) for breast cancer had a better result, with a lowest value of 96.24. For one of the prostate cancer patient treated with 3 arcs, there are two arcs had a GAI value below 90%.Conclusions: It is an easy and feasible way to apply the EPID with Epiqa software as dosimetry verification tool for VMAT. We will gather more clinical data to come out a better dosimetry verification procedure for VMAT in the near future.

並列關鍵字

Electronic Portal Imaging Device (EPID) ； Gamma Agreement Index (GAI) ； Volumetric Modulated Arc Therapy (VMAT) ； Dosimetry Verification