针对患者调强放射治疗计划的剂量学验证

目的建立针对调强放射治疗患者的剂量学验证方法。方法对100例患者进行的剂量验证共有3个测量项目一是采用小灵敏体积的电离室在仿人形模体中测量靶区剂量参考点(一般是射野等中心点)的绝对剂量,二是采用胶片测量一个治疗计划的所有射野在仿人形模体内形成的复合剂量分布,三是采用胶片或半导体探测器阵列在干水模体中测量单个射野的强度分布。由于完成全3个测量项目占用机器的时间过长,实际操作时采用自适应的方式,即首先测量靶区剂量参考点的绝对剂量,如果剂量误差在允许范围内,则不再进行其他的测量;如果剂量误差超出允许范围,则增加两个电离室测量点,并采用胶片测量横断面的剂量分布和(或)射野强度分布。结果93%患者的计划可以顺利实施,其他患者的计划需要调整铅门位置或完全重新设计。87%患者计划的剂量误差在临床可以接受的范围内,其他患者的计划需要对射野机器跳数进行修正;修正系统误差后,有96%患者计划的剂量误差在临床可以接受的范围内。结论利用已有的设备条件建立了患者调强放射治疗计划的剂量学验证方法,这种方法随着设备条件的改善和经验的积累还会进一步完善。针对患者的计划进行剂量学验证是很有必要的。

Plan-specific dosimetric verification for patient treated with intensity-modulated radiation therapy

Objective To establish a method of plan specific dosimetric verification for patient treated with intensity modulated radiation therapy Methods Here we describe the procedure developed in the Cancer Institute (Hospital) of Chinese Academy of Medical Sciences, and present the verification results of 100 patients.This procedure is composed of three kinds of measurements that are the absolute dose at the reference point of target volume with an ionization chamber of small sensitive volume, the relative dose distribution in a transverse plane with film, and the intensity map for each individual beam also with film. Because it took long to perform all three measurements together, we adopted an adaptive strategy. It means that we started with measurement of absolute dose at the reference point. If the dose error was within the preset tolerance (5%), we would not perform any other measurement. Otherwise, we would measure the absolute dose at two more points and measure the relative dose distribution and (or) intensity maps. Results The plans of 93% patients were deliverable while the other plans needed minor modifications or complete redesign. 87 % and 96% of plans did have dose errors within tolerances before and after correction of systematic error. Conclusions We have developed a dosimetric verification procedure, and will continue to improve it. Our experiences show that the procedure is indispensable under the current situation.