医用直线加速器治疗床对放疗剂量影响的研究

Research of Effect for Medical Linear Accelerator Treatment Table on Radiotherapy Dosimetry

目的探讨西门子医用直线加速器治疗床对放疗剂量影响的研究。方法将固体水模固定在治疗床中心处,改变加速器机臂的角度,从不同角度照射并用剂量仪进行比对测量,计算出治疗床不同床板对放疗剂量的衰减因子。结果西门子医用直线加速器治疗床中有机玻璃床头板对剂量的衰减在1.5～20.5%,有机玻璃床体板对剂量的衰减在1.9～38.6%,有机玻璃网状窗体板对剂量的衰减在0.18～12.3%。结论放射治疗时正后野180°左右时应选用网状板或有机玻璃床头板,在后侧斜野110°～130°和230°～250°区间最好用床尾板,并对相应剂量做出修正与补偿,而治疗床的主支撑架及金属边柜对剂量的衰减高达12.3～38.6%,而床头延伸板对剂量的衰减在1.1～5.5%之间,因此头部的肿瘤应选此延伸板治疗。因此在治疗计划设计与实施过程中应避免射线束直接穿过主支撑架与金属边框。

Objective To investigate the effect of radiotherapy dosage caused by the SIEMENS medical linear accelerator table. Methods The solid water phantom was fixed in the center of the table , and changed the angle of the machine arm. The chamber dosimeter was used to measure the dose from different angle , the factor of dosage declined by the different table planks was calculated. Result The radiotherapy dose was declined on the average by 1.5 -20.5 %, 1.9 -38.6%, and 0.18 - 12.3 % when the plexiglass table head plank , plexiglass table body plank and plexiglass web winder body plank in the SIEMENS medical linear accelerator table were used re- spectively. Conclusions The web table plank or plexiglass table head plank must be chose in the radiotherapy of the positive back field about 180°, in the back -flank field about 110° - 130° or 230° -250°chose the table tail plank is the best method , and should be rectified and revised by dose compensate . When beam passed through the metal handle and main support shelf of the table, it would reduce the dose by 12.3% -38.6% ,but the head ex- tending table plank reduce the dose by - 1.1% - 5.5 %, so it must be chose in the head tumor radiotherapy. In the process of designing and practicing the treatment plan should keep the beam away the metal handle of the bed or the mental support of the table plank .