逆向计划调强适形放射治疗的质量保证

Clinical quality assurance of intensity modulated radiation therapy

目的 通过一系列调强验证方法的研究 ,探讨逆向计划调强适形放射治疗 (IMRT)的质量保证方法是否可行。方法 用VarianCadplan三维治疗计划系统中Helios逆向计划系统对前列腺癌、鼻咽癌、脑瘤、胰腺癌、椎骨转移癌等设计并进行IMRT。为验证计划系统生成的各个照射野注量图与实际注量图的一致性 ,将剂量胶片放在平板有机玻璃体模下 ,使计划中的各个照射野始终垂直于体模表面 ;调用患者治疗数据分别单独照射 ,冲洗胶片后与计划得出的注量图进行比较。将剂量胶片夹在仿真体模适当的部位 ,调用患者治疗数据对体模进行模拟照射 ,由此得出轴向截面上的等剂量分布 ,与计划的等剂量曲线拟合比对。用电离室和水箱验证等中心和偏离点的绝对剂量。在模拟机或加速器上拍正侧位照射野验证片 ,与CT模拟数字重建的射线影像片比较 ,验证等中心位置。结果 各射线束轴垂直方向测得的注量图与计划系统计算的一致 ;等中心点绝对剂量测量的结果与计划计算的误差在 3%以内 ,偏离点绝对剂量误差较大 ;轴向截面等剂量曲线分布的胶片测量结果与计划计算的很接近 ;等中心位置误差在 3mm以内。

Objective To evaluate the clinical feasibility of quality assurance of intensity modulated radiation therapy(IMRT) through a series of clinical case studies. Methods Helios inverse planning system was used to provide optimized IMRT treatment plans for brain tumor, nasopharyngeal carcinoma, pancreatic cancer, spinal metastatic tumor and prostatic cancer. To verify the conformation between the fluence map of each beam predicted by the planning system and that actually delivered, a piece of film under a homogeneous polystyrene phantom was irradiated vertically with each of the beams to record the deposited dose. This measured fluence map was compared with that predicted by the planning. The dose distribution was recorded by irradiating the film in an anthropomorphic phantom using patients' treatment plan, then compared with that predicted by the planning. An ionization chamber in a water phantom was used to measure the central point dose and another eccentric point dose. Results The fluence map measured by the film was well consistent with that predicted by the planning. The error between the measured dose and predicted dose in the central point was less than 3%, whereas the error of the dose in another eccentric point varied greatly. The isodose distribution (on axial plane) measured by the film was consisent with the predicted one. Conclusions The procedures for quality assurance of IMRT are feasible in our experience.