電腦斷層治療機以不同射束阻擋方式治療肝腫瘤之劑量學評估

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 V_5 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.