Elekta Infinity直线加速器治疗床对放疗剂量的影响

目的:研究Elekta Infinity直线加速器治疗床在常用X射线能量下对放疗剂量的影响。方法:将圆柱体模体分别置于碳纤维主治疗床、延长板以及治疗床与延长板衔接处正中,旋转机架,分别让6和10 MV高能X射线穿过治疗床,利用指形电离室测量固体水中间的绝对剂量,得出不同角度下的剂量分布,并计算治疗床对X射线的衰减因子。结果:治疗床与延长板衔接处在120°和240°两个机架角处的剂量衰减因子在6和10 MV两种治疗模式下分别达到了36.02%和36.01%以及30.46%和30.63%,而当机架角为140°~220°时,衔接处与主治疗床的剂量衰减因子相近,在6与10 MV能量下的剂量衰减因子平均值及标准差分别为2.56%±0.49%和2.14%±0.39%以及2.55%±0.48%和1.95%±0.41%,机架角由180°增大或减小时两处的剂量衰减均呈上升趋势,二者均在120°和240°附近达到最大;6和10 MV两种能量下延长板在该角度区间的剂量衰减因子平均值及标准差分别为1.55%±0.24%和1.07%±0.25%,并在115°和245°附近达到最大值,剂量衰减因子分别为4.08%和3.97%以及3.20%和3.34%。结论:后斜野主体部分在主治疗床与衔接处对剂量的衰减低于3%,在延长板处对剂量的衰减小于2%,但在120°和240°附近以及115°和245°附近3处位置的剂量衰减会达到最大,需在计划系统中考虑床的影响;此外,主治疗床与延长板衔接处在120°和240°附近对剂量的衰减急剧增大,不适合作为治疗区域,在治疗病人时需注意避免将靶区移到该区域。

Effects of the carbon fiber couch of Elekta Infinity linear accelerator on radiotherapy dose

Objective To investigate the effects of the carbon fiber treatment couch of Elekta Infinity linear accelerator on radiotherapy dose.Methods Polymethyl methacrylate cylinder phantoms were put on the centers of main treatment couch,extension board and the joint area of them,separately.The gantry was rotated at different angles to beam 6MV and 10MV X-rays to penetrate the carbon-fiber couch,and a thimble chamber was utilized to measure the absolute dose in the cylinder phantom.The dose distribution at each angle was recorded and the X-ray attenuation factor of the treatment couch was calculated.Results At the gantry angles of 120°and 240°,the attenuation factors at the treatment couch reached 36.02%and 36.01%under 6 MV,and those at the joint area were 30.46%and 30.63%under 10 MV.The attenuation factors at the joint area and main treatment couch were close during the gantry angle between 140°and 220°,and the average value and standard deviation of their attenuation factors were 2.56%±0.49%and 2.14%±0.39%under 6 MV,and 2.55%±0.48%and 1.95%±0.41%under 10 MV.The attenuation factors at the joint area and main treatment couch were both increased when the gantry angle was increased or decreased from 180°,and reached the maximum around the gantry angles of 120°and 240°.The average value and standard deviation of the attenuation factors at extension board under 6 MV and 10 MV in the same angular intervals were 1.55%±0.24%and 1.07%±0.25%,respectively,and the largest attenuation factors were found at the gantry angles of 115°and 245°,with 4.08%and 3.97%under 6 MV,and 3.20%and 3.34%under 10 MV.Conclusion For the main part of posterior oblique field,the X-ray attenuation factors were below 3%at main treatment couch and the joint area,while it was below 2%at extension board.However,the attenuation effect reached the maximum at the gantry angles of 120°and 240°,115°and 245°,which make the carbon fiber couch must be considered in treatment plan system.Moreover,the joint area is not suitable for clinical treatment for it dramatically affects the delivered dose at the gantry angles of 120°and 240°,and the target area should not appeared in this area.