医用加速器反光镜的替代及对X线PDD的影响

目的探讨国产玻璃镜片替代进口加速器反光镜后,对射野等中心、对称性、均整性、重合性及MV级X射线百分深度剂量的影响。方法在不同厚度和材质的镜片及机头不同角度条件下,使用胶片法及三维水箱OAR、PDD测量法进行数据采集,分析比较不同镜片的影响情况。结果普通玻璃4mm镜片对射野PDD影响误差最大为6%;经8MVX线720Gy剂量照射后,灯光野出现双影十字线,亮度变暗。石英玻璃1.5mm镜片对射野PDD、OAR、等中心无明显影响,PDD误差<1%。接受同等剂量,灯光野无明显变化。结论普通4mm玻璃镜片不宜作MV级X线医用加速器的反光镜。采用薄型石英玻璃替代进口加速器反光镜较佳,PDD误差小。

Impact on the PDD of MV X-Ray for the Glass Mirror in Linac

Objective To explore the effect on the iso-center and OAR and PDD of the MV class X-ray coming from the linac when we use the glass mirror to replace an imported one. Method Data collected by using a film and 3D water phantom OAR and PDD measuring methods based on the different conditions. Comparison and analysis of the effect levels for different thickness and material mirrors are made. Result The PDD max error of the 4mm general glass mirror is 6%.When the 8MV X-ray 720Gy irradiation is given, the light f ield appears a dual cross lines and has darker brightness. The PDD max error of the 1.5mm quartz glass mirror is less than 1%. When it accepts the equal radiation dose, the light f ield iso-center and OAR and f ield brightness are agreed well with clinical demands. Conclusion Our practice shows that the 4mm general glass mirror can't suffer the MV class X-ray irradiation but the thin quartz glass mirror can. So the thin quartz glass mirror can be used for the linac.