一种采用辐射显色胶片EBT3和ImageJ软件确定环形施源器驻留位置偏移量的方法

A method for determination of dwell position offset of ring applicator using GafchromicTM EBT3 film and ImageJ software

目的报告一种采用辐射显色胶片和ImageJ软件确定环形施源器驻留位置偏移量的简便方法。方法在虚拟计划中，根据核磁（MR）标记线逐点手动重建环形施源器，最远端的重建点在MR标记线的末端，偏移量设为0。在2．5mm的步长下激活第1、11和23驻留点，给定相同驻留时间。摆位辅助图像由垂直相交的两个细线和一个直径为16mm的圆组成，用胶布将其与辐射显色胶片粘在一起。根据摆位图像将环形施源器与胶片固定后执行虚拟计划。使用垂直三脚架将胶片影像数字化后，导人ImageJ软件，使用“团块中心”功能半自动识别曝光中心。该测试重复5次，每次间隔1周。结果虚拟计划中第1个驻留点的半径与x轴的夹角为43°，实测结果该角度为（46．8±0．9）°。根据计算，环形施源器与该MR标记线联合应用时的偏移量是0．9mm。第1、11、23驻留点的半径分别为（12．9±0．1）、（12．5±0．1）和（12．4±0．1）mm。结论 使用辐射显色胶片和ImageJ软件来验证环形施源器偏移量是一种简便且精确的方法。

Objective To report a simple method for determination of dwell position offset of ring applicator using GafchromicTM EBT3 film and ImageJ software. Methods In the dummy plan, this study reconstructed the ring applicator point by point manually according to the MR line marker, the most distal reconstruction point was at the end of marker, set the offset to zero. The first, eleventh, and twenty-third dwell positions were activated with the step length of 2.5 ram. A setup image was designed to immobilize the ring applicator. The setup image was composed of two perpendicular thin lines and a circular with a diameter of 16 ram. GafchromicTM EBT3 film was fixed behind the setup image by plastic tapes. After irradiation, a ruler was put on the bottom of the irradiated film as a plotting scale. Photos were taken with the help of a vertical camera using a tripod. The file was imported into ImageJ software and the coordinate values were obtained by semi-automatic recognition of the center of exposure area. The test was repeated five times at one week interval to evaluate the uncertainty. For every time, each dwell position was measured five times. Results The angle between the radius of the first dwell position and the x-axis was 43° in the dummy plan, and （46.8＋0.9）° for actual measurement. The offset was 0.9 mm for the ring applicator combined with the MR according to calculation. The distances between the first, the eleventh and the twenty-third dwell positions and the center of the ring were （12.9 ± 0. 1 ） ram, （12.5 ± 0. 1 ） ram, （ 12. 4 ± 0.1 ） ram, respectively. Conclusions Using GafchromieTM EBT3 film and the ImageJ software is a simplified method to validate the dwell position offset of the ring applicator.