EBT剂量胶片测量电子线百分深度剂量的应用研究

目的 研究EBT剂量胶片在临床电子线百分深度剂量(PDD)中的测量方法.方法 采用14.7 cm×5.1 cm的矩形射野,在同一张EBT胶片上进行5阶梯度的剂量刻度.应用上述刻度方法,针对4、6、8、10、12和15 MeV电子线,在小水箱中采用竖直和倾斜5°两种方式测量PDD,并与半导体探头的三维水箱扫描结果以及平行板电离室在小水箱中测量结果进行比较和分析°结果当剂量胶片上端与水面平齐时,EBT测量的PDD曲线与两种探头测量的结果具有较好一致性,并且倾斜和竖直测量两种方式无明显差异.当剂量胶片上端伸出水面时,在竖自测量方式下剂量建成区内测量结果明显低于其他测量结果,而倾斜测量方式下则无明显影响.结论 新的剂量刻度方式快捷可靠,可显著减少剂量胶片用量.在测量电子线PDD时建议将胶片倾斜一定角度进行,以便减小胶片上端与水面不平齐所引起的测量误差.

GafChromic EBT in measurement for percent depth dose of high-energy electron beams

Objective To evaluate the dosimetry of high-energy electron beams by using GafChromic EBT film. Methods The percent depth doses of electron beams of 4 MeV,6 MeV,8 MeV,10MeV, 12 MeV and 15 MeV were measured with EBT. The results were then compared with the measurements with diode detector in RFA and parallel plate chamber in water tank. Results The percent depth dose curves using EBT film had a good agreement with those using the other two detectors. Furthermore, no differences were found between up-right and tilt setup methods. When film upper edge is higher than water surface, a sharp drop of measurement results using EBT film was observed in comparison with those from diode detector in build-up region. Conclusions EBT film can be applied to measure percent depth doses of high-energy electron beams. During the EBT film measurements, the film should be tilted at the angle of 5degrees to the central axis of the field. When choosing up-right setup method, the edge of the film should be parallel to the water surface.