目的：電腦斷層治療為一種旋進式的強度調控放射治療技術，藉由多葉式準直儀搭配治療床的連 續移動來達到高度順型的劑量分佈，本實驗的目的為肝腫瘤使用不同射束阻擋方式所呈現的治療 計劃結果比較與劑量驗證準確度之評估。 材料與方法：本次實驗是利用回溯性的方式選取 10 位肝腫瘤病人之電腦斷層影像重新執行治療計 劃，每位病人分別使用None（without block）、Directional block 及Complete block ，來限制射 束進出的角度，以保護鄰近的器官。治療計劃劑量驗證使用Exradin A1SL 游離腔量測絕對點劑量 及使用EBT3 底片來做二維相對劑量之量測。 結果：治療計劃結果顯示沒有使用任何射束阻擋的治療計劃能提供較佳的計劃靶體積包覆及劑量順 型度與均勻度，治療計劃平均監測單位（monitor unit, MU）數 none（without block）、directional block 及complete block 依序為3338.1 、3871.7 、4761.4 MU， 平均治療時間為237.26 、 273.64、334.29 秒，正常肝組織的V5 依序為81.8%、71.8%、57.5%，其他鄰近危急器官胃、 十二指腸、腎臟、小腸、脊椎的劑量都遠低於劑量限制，治療計劃驗證結果在點劑量皆符合 ±3% 的基準內，二維相對劑量之伽傌通過率分別為 96.7±2.2%、95.8±2.8%、94.6±3.8%。 結論：使用射束阻擋directional block 能提供不錯的腫瘤劑量順型度與劑量均勻度，也顯著地減 少正常肝組織所接受到的劑量，治療時間增加的比例約比without block 增加15%，對於整體的治 療時間增加不多，在劑量驗證的結果不論在絕對點劑量與平面劑量的量測與治療計劃的結果一致 性皆很高，directional block 對於慢性肝炎帶原肝腫瘤的病人提供一個可選擇的治療方式。

Purpose : Helical tomotherapy (HT) is a intensity-modulated radiotherapy treatment (IMRT) delivery system that achieves high dose conformality by multileaf collimator motion during treatment. The goal of this study was to evaluate the plan quality and delivery accuracy of the Hi-Art system with different plan parameters for the treatment of hepatocellular carcinoma. Materials and Methods : A total of 10 cases were analyzed in this study. Three HT treatments plans were generated for each case in the setting of without block, directional block and complete block respectively to adequately treat the planning target volume and spare the organ at risk. Patient delivery quality assurance (DQA) is an essential task to ensure the accuracy of doses delivered to the patients. The absolute point dose was measured with an Exradin A1SL ion chamber and Tomoelectrometer (Standard Imaging, Middleton, WI) which can be positioned anywhere along the central axis of the phantom, and Gafchromic EBT3 films were placed in the coronal orientation to acquire the planar representations of dose distribution. The measurements were analyzed using the gamma evaluation with the 3% dose and 3 mm distance criteria. Results : The results demonstrate that without block was capable of providing more uniform target doses. The conformation number and homogeneity index of plans without block were better than directional block and complete block. The average MUs was 3338.1, 3871.7, 4761.4 MU, and the delivery times was 237.3, 273.6, 334.3 seconds respectively. The V5 values for the normal liver was 81.8%, 71.8%, 57.5%. All of the cases passed the 3% point dose difference criteria. The 3% / 3 mm average gamma passing rate was 96.7 ± 2.2%, 95.8 ± 2.8%, 94.6 ± 3.8% for without block, directional block and complete block respectively. Conclusions : The results of this study had demonstrated that the three types of plans can be delivered accurately based on their own QA standards. The major advantage of directional block is to reduce the low dose region of normal liver and just increased approximately 15% of delivery time. The directional block can provide a good choice to the HCC patients with chronic hepatitis.