绝对剂量的偏移对MatriXX剂量验证结果的影响

Influence of Deviation in Absolute Dose on Verification Results of MatriXX

目的探讨加速器绝对剂量的偏移对调强计划射野的Matri XX剂量结果影响。方法选取24例宫颈癌患者调强计划中机架角度为180°的射野(记为G180),生成验证计划,在Varian Clinac i X加速器上实施,使用二维电离室矩阵Matri XX进行测量。通过Omni Pro I’m RT软件,模拟绝对剂量的偏移(记为d),d在-10%~10%取值,间隔1%,观察相应Matri XX剂量验证结果变化。结果总体上看,绝对剂量向正负方向偏移时,Gamma通过率下降,平均Gamma值变大。本研究中,Gamma通过率的最大值并不在d=0处,而在d处于-3%^-1%之间;平均Gamma值最小点在d处于-3%~0之间。结论绝对剂量的偏移对调强计划射野的Matri XX验证结果有一定影响,在分析Matri XX剂量验证结果时,应将绝对剂量的偏移因素纳入考虑中,同时在放疗日常工作中,应定期检查校准加速器的绝对剂量。

Objective To discuss the influence of deviation in absolute dose on verification results of IMRT fields of MatriXX.Methods Fields with gantry angle180°(G180)were selected for24patients with cervical cancer,and corresponding verificationplans were created.The verification plans were implemented in the Varian Clinac iX linear accelerator,and the dose distributionswere measured by the two-dimensional ionization chamber array(MatriXX).OmniPro I’mRT software was used to simulatethe deviation in absolute dose(d),and d ranged from-10%to10%with interval of1%.Corresponding dose verification resultswith different values of d were analyzed.Results By and large,gamma passing rate was decreased and value of average gammawas increased when absolute dose deviated to positive or negative directions.The maximum gamma passing rate was not in theposition with d=0,but in the range of-3%to-1%,and the values of d were in the range of-3%to0when average gamma achievedthe minimum value.Conclusion Deviation in absolute dose has a significant influence on verification results of IMRT fields ofMatriXX.When analysing verification results,the factor of deviation in absolute dose should be taken into consideration.In routinework of radiotherapy,the absolute dose of Clinac accelerator should be calibrated regularly.