基于模拟退火算法的加速器能谱重建

Energy Spectrum Reconstruction of Accelerator Based on Simulated Annealing Algorithms

目的:采用模拟退火算法针对某加速器光子韧致辐射谱进行能谱重建,为后续剂量计算打下基础;方法:利用某加速器6MV、18MV能量5×5射野下的实验PDD数据结合蒙卡程序EGSnrc输出的不同能量下的单能PDD,采用模拟退火算法合成了加速器出束口能谱。针对国内某型加速器进行蒙卡建模,比较了合成能谱和某型加速器出射能谱的形状,计算了相关系数。最后,利用蒙卡程序以模拟退火算法合成的能谱为源项,对蒙卡模拟PDD数据和实验PDD数据进行了比较。结果:合成能谱和某型加速器出射能谱的形状相似,模拟退火算法反推的能谱和原始能谱相关系数大于0.99,EGSnrc采用反推的能谱进行合成计算得到的PDD数据和实验PDD数据之间的相关系数大于0.99995;结论:利用模拟退火算法可以在治疗用加速器能谱未知的前提下利用实验测量的PDD数据进行能谱重建,且重建得到的能谱可靠性很高,便于后续的剂量计算。

OBJECTIVE To reconstruct the photon bremsstrahlung spectra of an accelerator by simulated annealing algorithm,and to lay a foundation for subsequent dose calculation.Methods Using the experimental PDD data of a certain accelerator at 6 MV and 18 MV energy of 5*5 radiation fields and combining with the single energy PDD of different energy simulated by the Monte Carlo program EGSnrc,Energy spectrum of accelerator exit is synthesized by simulated annealing algorithm.Monte Carlo Model of a domestic Accelerator was built.The shape of the synthetic energy spectrum and the MC energy spectrum of an accelerator were compared and the correlation coefficient was calculated.Finally,using the energy spectrum synthesized by simulated annealing algorithm as the source term,the Monte Carlo simulation PDD data and experimental PDD data were compared.The correlation coefficient was calculated.Results The shape of synthetic energy spectrum was similar to that of an accelerator.The correlation coefficients between simulated annealing algorithm and original energy spectrum were greater than 0.99.The correlation coefficients between synthetic PDD data and experimental PDD data were greater than 0.99995.Conclusion The simulated annealing algorithm can be used to reconstruct the energy spectrum from the measured PDD data without knowing the energy spectrum of the accelerator.The reconstructed energy spectrum has high reliability and is convenient for subsequent dose calculation.