R620-ACF型腹部碳纤维托架对直肠癌调强放射治疗剂量的影响

目的：研究R620-ACF型腹部碳纤维托架对射线的衰减率和此碳纤维托架对直肠癌放射治疗计划剂量的影响,为使用腹部碳纤维托架进行体位固定的直肠癌调强治疗计划制定提供指导性意见。方法：（1）用电离室测量R620-ACF型腹部碳纤维托架不同位置处对射线的衰减率。（2）首先,利用治疗计划系统在不考虑腹部托架影响的情况下制定一组治疗计划;然后不改变此计划的子野、机器跳数等参数,将腹部托架包括到计算域内进行剂量计算,比较两个计划的剂量评估指标D95、Dmin、Dmax、Dmedian的差异。结果：（1）R620-ACF型腹部碳纤维托架不同位置处的衰减率各不相同,每个测量点的衰减率都大于2%,衰减率最高达到了28%。（2）不考虑托架衰减影响制定的调强计划经过腹部托架的衰减后,靶区GTV的各项评价指标D95、Dmin、Dmax、Dmedian等剂量值均下降超过2.4%,不同射线入射角度有差异,最大影响可以使GTV的D95减小7.9%。结论：R620-ACF腹部碳纤维托架对射线有很大的衰减,为减少其对调强放射治疗剂量的影响,在调强放射治疗计划制定过程中必须将其包括在计算区域内参与优化与计算。

Dosimetric Impact of Carbon Fiber Abdomen Board for Rectal Cancer in IMRT

Objective：The objective of this study was to research the X-ray attenuation rates of R620-ACF carbon fiber abdomen board,and evaluate the dosimetric impact on rectal cancer by using R620-ACF carbon fiber abdomen board in IMRT treatment plan and provide guidance on these.Methods：（1） Measure the attenuation rate in different parts on carbon fiber abdomen board by using ionization chamber.（2） Formulate a group of IMRT plan without consideration of carbon fiber abdomen board and the group of experimental plans were constructed using the same criteria,including monitor units,subfields,with carbon fiber abdomen board in it,then compare the difference of two groups on D95,Dmin,Dmax,Dmedian in IMRT plan.Results：（1）The attenuation rates were along with different parts on R620-ACF carbon fiber abdomen board at lowest 2% and highest 28%.（2）All the related dosimetric evaluation ofGTV were reduced at least 2.4% in experimental plans.Different incident angle of radiation beams turns out various reduction at highest 7.9% on D95 of GTV.Conclusions：The attenuation rates of R620-ACF carbon fiber abdomen board should be considered due to the major dosimetric impacton IMRT treatment plan.