应用辐射直接显色剂量胶片测量高能光子线的表面和建成区剂量

Surface and Build-up Region Dose Measurement Using Radiochromic Film for Megavoltage Photon Beam Irradiation

目的:准确测量高能光子射线剂量建成区的剂量分布,评估三维水箱扫描深度剂量曲线在表浅部位的误差。方法:使用辐射直接显色胶片(EBT胶片)测量加速器6MV光子线由体模表面到最大剂量深度区间的建成剂量分布,并与传统的电离室和半导体探头三维水箱扫描百分深度剂量曲线在该区间的剂量分布进行比较。结果:在接近最大剂量深度的区间(0.6cm～Dmax),EBT胶片与三维水箱扫描测量结果非常接近,差别小于2%;在电离室和半导体探头的有效测量深度至0.6cm深度区间,对不同射野大小,EBT胶片测量值大于两种三维水箱测量值5%～10%;在小于电离室和半导体探头的有效测量深度的区间,EBT胶片的测量值与水箱扫描结果比较差别最大分别达到22.7%(半导体探头)和49.3%(电离室)。结论:EBT胶片可以用于准确测量表面和建成区剂量分布,三维水箱扫描得到的PDD曲线应该进行建成区修正。

Objective： To accurately measure the surface and build-up region dose distribution of megavoltage photon beam irradiation, and evaluate the measurements performed in a 3D waterphantom system. Methods： Build-up region dose distribution of 6 MV photon beam was measured with both radiochromic film and detector （ion chamber and diode） in water phantom scanning system. The differences were compared for determine the limitation of detector scanning in this area. Result： No obvious difference between the film measuring and the detector scanning were found in the depth region of 0.6 cm-Dmax （diff〈2%）. The film measuring results were 5% to 10% bigger in depth between the effective depth of detectors to 0.6 cm depend on the field sizes, in region beyond the effective depth of detectors, the maximum differences between film measuring and detector scanning were 22,7% for diode detector and 49.3% for ionization chamber. Conclusions： Radiochromic film can be used to measure the surface and build-up region dose distribution accurately. Depth dose measured with detector scanning in waterphantom need to be corrected in the region very close to surface.