逆向计划调强放射治疗的临床验证

Clinical Verification of Inverse Intensity Modulated Radiation Therapy

目的:探讨逆向计划调强放射治疗IMRT临床治疗前的验证方法。方法:用胶片法验证Cadplan(包括Helios逆向计划系统)三维治疗计划系统生成的各个照射野注量图与在Varian23EX直线加速器(安装120叶MLC)照射中实际释放的注量图的一致性;用电离室法验证等中心绝对剂量计算值与实测值的符合性。结果:等中心绝对剂量的误差小于5%,符合临床要求;各射束轴垂直方向测得的注量图与计划系统计算的注量图一致;等中心位置验证显示,CT模拟的正侧位DRR片与加速器正侧位验证片误差在±2 mm以内。结论:Varian逆向调强放射治疗系统符合临床要求。

Objective： To evaluate Clinical verification of inverse intensity modulated radiation therapy（IMRT）, Methods： To verify whether the fluence map of each beam desired by Helios inverse planning system was actually delivered in Varian 23 EX Linear accelerator with 120 leafes collimatorMLC, a piece of film under a homogeneous polystyrene phantom was irradiated vertically with each of the beams to record the deposited dose, which is the fluence map actually deliverd. The ionization chamber in a water phantom was used to measure the central point dose and another point dose. Results： The fluence maps measured by the film were well consistent with that predicted by the planning. The error between measured dose and predicted dose in the central poifit was less than 3%, but the error of dose in another point varied more widely. The film measurements of the isodose distributions （on axial plane） coincided with the predicted distributions. Verification on Accuracy of isocenter location was done by measurement and comparing the distance between the isocenter and anatomy mark in DRR films from CT simulator and verification films from Varian 23 EX Linear accelerator. The difference in setup is less than ±2 mm. Conclusions： the present investigation shows that the IMRT delivered by Varian 23 EX Linear accelerator with 120 leafs collimator（MLC） is available.