螺旋断层放疗系统剂量学参数变化检测与靶耗损的相关性研究

Study on The Correlation Between Dosimetric Parameters Change and Degradation of Target for Tomotherapy System

目的:通过胶片检测的横向截面剂量曲线形状变化并结合输出量和能量测量,探讨螺旋断层放疗系统中靶的耗损过程伴随的剂量学参数变化之间的关系。方法:横向截面剂量曲线的胶片检测按照月检或更高的检测频率,以5月份的曲线数据作为标准,其它与之相比和评估。静态输出量的测量采用日检频率,采用源皮距85 cm,照射野(50×40)cm条件下,长方体等效固体水1.5 cm深度处的固定机架测量值。能量测量采用周检或日检,分别计算模体中线深度处的D10/D1.5和D20/D1.5,评估射线质的变化情况。结果:以5月4日曲线数据为基准,对有效曲线线段的截取和一致性比较表明,先期变化缓慢,换靶的前一个月平均值差异显著增大。输出量在2%的偏差范围内,但7、8和9月上旬出现输出量的负向偏差,然后自动恢复正常10天左右,急剧下降。整个测量中的射线质基本在允许误差范围内变化不明显。结论:近6个月的测量分析表明,胶片法可以反映剂量射野的截面剂量曲线形状变化情况,并结合输出量等的检测可以用于靶耗损程度的判断,具有一定的规律性。可以作为用户能够独立开展的为螺旋断层放疗系统质控的一部分。

Objective： To discuss dosimetric parameters change with the degradation of target by shape change of film transverse beam profile,dose output and energy measurement. Methods： Transverse beam profiles were measured monthly or higher fre- quency. All data of films could be compared and evaluated with the standard data of May. Static dose output were monitored on a daily basis, with 1.5 cm depth measurement point in virtual water at an 85 cm SSD and field size （50×40） Cmo Energy was calculated monthly or weekly by D10/D1.5 和 D20/D1.5. Results： Analysis of six months measurement shows that film method reflects the change of transverse beam profile, and can be used to evaluate the degradation situation of taget together with dose output. This method can be an item of quality control by user independently.