治疗床及体位固定装置对放疗剂量精确性的影响及解决方法  

Evaluating the impact of treatment table and immobilization device in IMRT planning accuracy

作　　者：郭妍妍[1] 蒋胜鹏[2] 戴越[1] 毕平[3] 李小东[1] 

机构地区：[1]天津医科大学第二医院放疗科,300211 [2]天津医科大学肿瘤医院放疗科,300060 [3]天津医科大学生物医学工程学院,300070

出　　处：《国际生物医学工程杂志》2015年第4期214-217,I0006,共5页International Journal of Biomedical Engineering

摘　　要：目的研究医科达PRECISE加速器C型臂型治疗床及体位固定装置对治疗计划射野剂量传递精确性的影响，并探索一种消除该影响的方法。方法将固体水和电离室进行cT扫描并将扫描图像传到治疗计划系统（TPS）中。在TPS中设置照射参数：选用6MV的x射线、100MU机器跳数，射野大小分别为5cm×5cm和10cm×10cm，从机架角0°开始，在0°～180°区间内每隔5°为间隔定义射野入射方向进行等中心照射。按照TPS中设置的条件分别测量带有及无治疗床C型臂和体位固定装置时的绝对剂量，将测量结果进行记录并分析。在MatriXX二维电离室矩阵系统上执行同样的照射野计划，使用OmniProFmRT软件中“add constant value”功能，找出最合适的增加总剂量的系数因子。选取6例盆腔肿瘤患者剂量增加前后的调强放疗计划验证该因子能否消除治疗床及体位固定装置对治疗计划射野剂量的衰减。结果放射治疗中加速器治疗床及体位固定装置对后斜野照射剂量衰减有一定的影响，在65°～70°和115°～125°两个人射范围对剂量的影响最大。根据实验分析结果，将计划的总剂量等比例向上归一，将总剂量增加2％，可弥补治疗床和体位固定装置对放疗剂量的衰减，提高总的射野通过率。结论在设计治疗计划中照射野的入射方向时，应尽量使机架角度避开65°～70°和115°～125°及对侧的290。～295。和230°～245°两个人射范围。由于治疗床和体位固定装置对后斜野照射剂量衰减有影响，因此应在TPS中针对剂量衰减值进行相应的剂量补偿。Objective To investigate the influence of treatment table with C-arm and immobilization device in IMRT planning accuracy, and to explore methods to solve this problem. Methods The solid water slabs and the ionization chamber was scanned and images were transmitted to the treatment planning system （TPS）. Beam parameters in the TPS were set with 6 MV beam and 100 MU exposures were used. Measurements were performed at two different sizes of 5cm×5 cm and 10cm×10cm. The grntry was rotated through angles from 0° to 180° with measurements taken at 5° increments. The measure point was set at center of the ionization chamber＂ measure point, which was also the central point of planning. The center axis of Matrix was aligned with the center of couch and was irradiated in accordance with the same conditions. OmniPro-I＇mRT software was used to compare and analyze the dose distribution of the radiation field of measurement and the treatment planning system output. Using the function of add constant value to find the appropriate coefficient to improve the plan total dose. The dose distributions for each beam in IMRT plans which was increased or unincreased total dose were measured for 6 patients with pelvic tumor respectively. Results In radiation therapy, treatment couch and immobilization device may attenuate radiotherapy dose. The impact of the incident range from 65°-70° and 115°-125° were the largest. Increasing the total dose of the treatment plan by 2% could compensate the attenuation of the treatment table and immobilization device. Conclusions In radiation therapy, the impact of the incident range from 65°-70°, 115°- 125° and another side of 2900-295° and 2300-245° should be avoided. The attenuation should not be neglected in the TPS and dose should be compensated by adjusting beams＇ MU.

关 键 词：治疗计划系统 治疗床 精确性 衰减 

分 类 号：R730.55[医药卫生—肿瘤]