【摘要】 利用深度剂量测量数据重建放射治疗X射线能谱,并对重建方法进行评价。先用Monte-Carlo模拟计算60个单能光子束的深度剂量分布作为基函数,然后使用Cimmino迭代法对测量的深度剂量进行线性拟合,得到相应射野每个单能光子束对测量深度剂量的贡献权重,即放射治疗所用的轫致辐射X射线的相对能谱。考虑机头组件散射对能谱的影响,计算中采用双源模型,在等中心平面分3个区域(5cm×5cm、10cm×10cm～5cm×5cm、20cm×20cm～10cm×10cm)重建能谱。最后将分区重建能谱与10cm×10cm射野重建能谱进行比较,对重建方法进行评价。结果表明:利用双源模型重建能谱更符合临床实际情况,分区能谱较不分区能谱计算的深度剂量更符合实际测量深度剂量。更多还原

【Abstract】 This study describes a method to reconstruct energy spectra of clinical bremsstahlung X-rays from measured depth dose data. The measured depth dose can be expressed as a linear combination of basis functions,namely the depth doses of monoenergetic photon beams derived from Monte-Carlo simulations. The weights of the basis functions,which were obtained with the Cimmino iteration,represent the relative energy spectra. The real energy spectra are changed gradually with the off-axis distance because of the photons scattered from components of treatment head. The energy spectra of X-rays in the isocenter plane were reconstructed using a dual-source model in three regions:5 cm×5 cm,10 cm×10 cm-5 cm×5 cm,20 cm×20 cm-10 cm×10 cm. Depth doses produced from the uniform spectrum (10 cm×10 cm) and from regional spectrum were compared with measured depth doses respectively. The results show that using the dual-source model in reconstructing spectrum is more appropriate in clinical,and depth doses produced from regional spectrum are more identical to measured depth doses.更多还原