碳纤床对光子射束的衰减及其修正因子

Attenuation of photon beam caused by carbon fiber treatment couch and related correction factor

目的:现今放射治疗使用的治疗床已改成质地更坚固且戴重负荷更佳的碳纤维材质。本实验主要探讨直线加速器的治疗射束经过碳纤床时的衰减性质及其修正因子。方法:本实验使用Varianix的直线加速器及其碳纤床,及一套自行设计的半径为11 cm的球形假体。把农夫型游离腔(Farmerion chamber)放置在直线加速器的等旋转中心点上,直线加速器机头以水平方向为初始角度,按顺时针旋转方向由下往上每隔5°照射一次,每次照射后测量射束在经过治疗床时的衰减系数,以及探讨如何修正此辐射剂量衰减值。结果:实验结果显示当治疗射束经过治疗床时最大的衰减量是4.9%,在经过配件的固定凹槽时会发生衰减量突减的现象。结论:当治疗病人的射束经过碳纤维床的固定凹槽时必须经过适当的射束衰减值修正量的修正才可得到正确的治疗监控单位。

Objective Nowadays, the treatment couch for radiotherapy is made from carbon fiber with stronger texture and better load capability. The attenuation of photon beam of linear accelerator caused by carbon fiber treatment couch and the related correction factors are discussed in the paper. Methods The linear accelerator and the carbon fiber treatment couch of Varianix, and a self-design ball phantom with a radius of 11 cm were applied in the study. Farmerion chamber was placed at the rotating isocenter of linear accelerator. The horizontal direction was taken as the initial gantry angle of the head of linear acceleration. Turn the head clockwise, irradiation from bottom to top was preformed every 5°. The attenuations of photon beam caused by carbon fiber treatment couch were measured after each irradiation. The method for correcting the attenuation was also discussed. Results The maximum attenuation of photon beam was up to 4.9%. At the fixed notch of parts, the attenuation showed significant reduction. Conclusion When the photon beam passes through the fixed notch of carbon fiber treatment couch, the appropriate attenuation correction should be applied to obtain the correct treatment monitor unit.