摘要
目的 基于XiO计划系统研究加速器碳素纤维治疗床对放射治疗剂量分布的影响，并通过在XiO计划系统中构建虚拟治疗床来模拟加速器治疗床对剂量的衰减。方法 使用大孔径螺旋CT扫描加速器治疗床的延长板，勾画轮廓并保存为床模型。将固体水模置于治疗床的中心，测量不同机架角度（100°～180°）下等中心处的吸收剂量，并在XiO计划系统中加与不加床模型的情况下分别进行剂量计算，得到治疗床的剂量衰减系数。通过不断调整外层碳素纤维（CF）和内层填充泡沫（FC）的相对电子密度（RED）值，得到能最好模拟治疗床剂量衰减的CF和FC的RED值。选取10例肺癌患者计划，使用Octavius 4D模体进行剂量验证，评估在剂量计算中考虑治疗床对计划通过率的改善。结果 CF和FC的最优化RED分别为0.75和0.10 g/cm^3。不考虑治疗床，计算值的偏差在120°达到最大值4.84%；考虑治疗床后，误差由（2.54±1.48）%降至（-0.04±0.36）%，差异有统计学意义（Z=-3.621，P〈0.05）。三维剂量验证的γ通过率（3 mm/3%标准）由（91.79±1.25）%提高至（94.74±1.69）%，差异有统计学意义（t=6.027，P〈0.05）。结论 治疗床对剂量的衰减不应被忽略，在XiO计划系统中构建虚拟治疗床可以很好地模拟衰减，提高剂量计算的准确性。
Objective To investigate the dosimetric effect of carbon fiber couch through virtual simulation in the XiO treatment planning system （TPS）. Methods A treatment couch model of iBEAM evo Extension 650 was scanned with a big bore spiral CT and its contour was stored in the XiO TPS. The attenuation coefficient of couch was obtained by measuring the attenuated dose with and without a solid water phantom on the couch at different gantry angles （100°-180°）. The optimal relative electron density （RED） values of the carbon fiber （CF） cover and foam core （FC） were adjusted according to the comparison between measured and simulated attenuation dose. The effects of the couch in the TPS on pass rate were evaluated by Octavius 4D phantom with 10 cases with lung cancer. Results The optimal RED values of CF and FC were 0.75 and 0.10 g/cm^3, respectively. The measured attenuation error was the maximal at gantry angle of 120° （4.84%） without the treatment couch in the TPS. The average measured attenuation errors without the couch in the TPS dropped significantly from （2.54±1.48）% to （-0.04±0.36）% after inclusion of the treatment couch during dose calculation （Z=-3.621, P〈0.05）. The three-dimensional dose verification γ pass rate （3 mm/3%） without the couch increased significantly from （91.79±1.25）% to （94.74±1.69）% after inclusion of the couch in the dose calculation （t=6.027, P〈0.05）. Conclusions The effect of couch on the attenuation dose is significant. Inclusion of a virtual model of couch in XiO TPS can simulate the attenuation effect properly and improve the accuracy of dose calculation.
出处
《中华放射医学与防护杂志》
CAS
CSCD
北大核心
2018年第1期21-25,共5页
Chinese Journal of Radiological Medicine and Protection
基金
国家自然科学基金（81227902）
