基于电子射野影像系统建立医用直线加速器晨检工具的临床测试

目的 利用电子射野影像系统（EPID）建立加速器快速晨检工具，并进行评估。方法 用Synergy加速器EPID测得10 cm×10 cm开野及楔形野图像，由Matlab提取并分析图像参数，实现快速晨检。对EPID剂量-机械重复性、灰度值与MU值线性、输出量及射野大小测量准确性测试，用电离室、EPID分别测量Synergy输出量随MU变化情况，用DailyQA3及研究中所开发的工具对Synergy进行2个月的监测。结果 EPID剂量重复性测试稳定，射野大小和中心测试精度分别为0.5和1.0 mm，平坦度和对称性测试精度均为0.17%；机械精度测试结果与剂量重复性测试一致。EPID对加速器输出剂量响应线性相关（R²>0.999）。EPID对输出剂量和射野大小的探测灵敏度较高。EPID与DailyQA3所有临床测试结果均在允许限值内，且两种结果一致。结论 EPID剂量-机械稳定性及响应线性均良好，输出量及射野大小监测结果均准确，研究中建立的晨检工具准确可靠。

Establishment and evaluation of a daily quality assurance tool for LINAC based on electronic portal image device

Objective To establish and evaluate a morning check system for linac based on electronic portal image device (EPID). Methods Delivered fluence maps of open and wedge fields at 10 cm×10 cm field size of Synergy Linac were measured by EPID. Figure features from these two images were extracted with matlab codes and analyzed to realize a quick morning check. The repeatability of dose response and mechanical setup, relationship between gray value and machine unit (MU), accuracy of output and field size test were investigated with both EPID and DailyQA3. The status of Synergy linac was monitored both by DailyQA3 and EPID for two months. Results EPID was able to test the linac consistently with a testing error of 0.50 mm, 1.00 mm for field size and center, respectively. Both of the test accuracy for flatness and symmetry was 0.17%. The mechanical accuracy test and dosimetric repeatability test were also consistent. The dose response of EPID was linearly related to the linac output (R²>0.999). EPID was highly sensitive to the change of output and radiation field size.The measurement deviations between EPID and DailyQA3 were consistent and within clinical acceptable tolerance. Conclusions EPID showed great accuracy and stability on monitoring the performance of linac. The established daily check tool based-on EPID is accurate and reliable for clinical usage.