调强适形放射治疗的剂量学验证

DOSIMETRIC VERIFICATION OF THE INTENSITY MODULATED RADIATION THERAPY

调强适形放射治疗(IMRT)是近年来发展的一项崭新的放疗技术,有关它的质量保证和质量控制是一个急需解决和必须重视的问题,而其中剂量学验证是极其重要的一方面。本研究的目的就是要探讨调强适形放射治疗过程中的剂量学验证方法,保证IMRT治疗计划临床实施的正确性。研究过程为选取10例需要实施IMRT的病人,利用CMS公司的Xio三维治疗计划系统设计出IMRT计划,用Cirs调强胸段体模作为验证体模,将病人的IMRT计划移植至体模生成QA计划,计算出选定验证点的绝对剂量和选定验证平面的相对剂量分布。在加速器上按QA计划条件摆位并实施照射,得到用0.6cc电离室实测的验证点绝对剂量和用GafChromicEBT免洗胶片拍摄的平面剂量片,用RIT113胶片剂量分析软件分析实测的和计划的平面相对剂量分布。10例病人的剂量学验证结果表明,绝对剂量误差在5%以内,相对剂量分布在高剂量区很接近,低剂量区有一定差别。

Intensity modulated radiation therapy （IMRT） is a technique developed of late years. The problem in quality assurance and quality control of IMRT and must be urgently resolved, of which dosimetry verification is one of most important aspects. The objective of this research is to discuss the method of the dosimetric verification in the process of intensity modulated radiation therapy and insure correctness of chnical IMRT practice. The way of research was first of all to choose ten patients who would be treated with IMRT, and CMS＇s Xio three dimensional treatment planning system was utilized to design IMRT plan. Then the Cirs intensity modulated thorax phantom was used as a verification phantom and the approved plan of IMRT for the patient was transplanted to the phantom to produce a QA plan, the absolute dose at verification points and relative dose distribution on verification planes were calculated. At last according to QA plan requirement, irradiation was carried out, the absolute dose at verification points was measured using 0.6cc ion chamber and plane dose film was developed using GafChromic EBT film. The actual measured and planned relative dose plane distribution were analyzed by RIT113 film measurement software. The results of experiments for ten patients show that the measured error of absolute dose is whthin 5 %, and the relative dose distribution is very approximate in high dose region and some differences exist in low dose region.