目的　探讨直线加速器放射损伤后自由基的改变情况。方法　采用直线加速器照射制作动物模型 ,同时观察其血清及局部组织中NOS、MDA、SOD、GSH -PX含量的改变。结果　电子直线加速器照射后MDA、NOS在一定剂量范围内上升 ;SOD、GSH -PX则在一定剂量范围内下降。结论　电子直线加速器照射后能产生自由基 ,并引起自由基清除酶系活性下降 ,但局部变化明显小于全身变化 ,这些改变是否可能为引起胶原损伤的原因 ,有待进一步研究。 Objective To investigate the changes of free radicals after radiation injury of linear accelerator. Methods The animal models were made by linear accelerator, and the contents of NOS, MDA, SOD and GSH-PX in serum and local tissues were observed. Results After exposure to electron linear accelerator, MDA and NOS increased in a certain dose range. SOD and GSH-PX decreased in a certain dose range. Conclusion Electron linac can produce free radicals and cause the activity of free radical scavenging enzymes decreased, but the local changes were significantly less than the systemic changes. Whether these changes may cause collagen damage remains to be further studied.