使用電子影像驗證裝置在弧形強度調控放射治療之劑量驗證

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

李秉倫(Pin-Lun Li)

指導教授 ： 趙敏

中臺科技大學/健康科學院/醫學影像暨放射科學系暨研究所/碩士(2012年)

https://doi.org/10.6822/CTUST.2012.00045

摘要

本研究分為兩大部分，先以田口方法探討電子影像驗證裝置的解析度，再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。
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位其它部位癌症。
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癌症平均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），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 ； 弧形強度調控放射治療 ； 加馬吻合指數 ； 劑量驗證

並列摘要

This thesis consists of two parts, one is investigate the resolution of Electronic Portal Imaging Device (EPID) using the Taguchi methodology, and the other part is dosimetry verification of RapidArc volumetric modulated arc therapy with EPID.
Dose distributions verification for RapidArc VMAT treatment plans can be done with EPID and its associated software, Epiqa. Epiqa software coverts the EPID images into dose map based on the GLAaS theory. 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 contributions of primary and transmitted radiations. By applying the conversion factors to all pixels of the EPID images, a planar dose distribution at the dmax in water is obtained. Twenty patients (70 arcs in total) were included in this study, 7 with prostate cancer, 2 with breast cancer, 4 with rectal cancer, 4 with NPC, and 4 with other sites. The Distance to Agreement (DTA) and the Dose Difference (ΔD) for The Gamma Agreement Index (GAI) of dosimetry parameters with EPID technique were set as 3 mm and less than 3%, respectively. The average GAI (%) 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. 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) ； Dosimetry Verification ； Volumetric Modulated Arc Therapy(VMAT) ； Gamma Agreement Index(GAI)

參考文獻

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