免冲洗胶片法测量后装机^192Ir放射源到位精度及步进距离精度

Flushing-free film test of ^192Ir accuracy of position and step distance for afterloading systems

目的研究使用免冲洗胶片测量后装机^192Ir放射源到位精度及步进距离精度的方法.方法 使用GAFCHROMIC（R）EBT3型免冲洗胶片对1台国产后装机^192Ir放射源到位精度及步进距离精度进行测量.曝光后的胶片使用EPSON PREFACTION V700 PHOTO胶片扫描仪扫描成胶片分析软件要求的图像格式,然后用SNC Patient 5.2软件中的胶片分析软件对图像进行分析.结果以源活性中心为基准点,该后装机使用胶片法测量的192 Ir放射源到位精度为-0.75 mm.免冲洗胶片分析方法能够分辨2个驻留点间5 mm的步进距离精度,不能够分辨2个驻留点间2.5 mm的步进距离精度;2.5 mm步进距离精度可通过测量3个连续驻留点第1点和第3点间距离是否为5 mm的方法进行间接判断.该后装机使用胶片法测量的连续9个驻留点间的5 mm步进距离无偏差;2.5 mm步进距离精度间接判断结果无偏差.使用胶片法测量的后装机^192Ir放射源到位精度符合国家标准要求.结论 免冲洗胶片方法可以用于后装机^192Ir放射源到位精度及步进距离精度的测量.

Objective To study the method of measuring the position accuracy and the step distance accuracy of afterloading system with ^192Ir source by using flushing-free film.Methods The position accuracy and the step distance accuracy of a China-made afterloading system with ^192Ir source was measured by using GAFCHROMIC （R） EBT3 flushing-free film.The film was scanned to proper image format,required by dose analysis software,by EPSON PREFACTION V700 PHOTO scanner.Then images are analyzed by using film dose analysis software in SNC Patient 5.2.Results With focus on the center of active section of source,the position accuracy of this afterloading system with192Ir source was-0.75 mm.Using film analysis could make the step point to tell apart if the step distance was 5 mm away by the method of film analysis,but couldnot make it to tell apart if the step distance was 2.5 mm away.The 2.5 mm step distance accuracy could be judged if the distance between the 1 st point and the 3rd point was 5 mm,then the 2.5 mm step distance could be deemed to no deviation.The 5 mm step distance of this afterloading system had no deviation in continuous 9 step points measured by flushing-free film.The indirect measuring results of the 2.5 mm step distance had no deviation as well.The position accuracy of this afterloading system measured with the flushing-free film accorded with the national standards.Conclusions The method of measuring the position accuracy and the step distance accuracy of the afterloading system with192Ir source by using flushing-free film is technically feasible.