Objective:To study the effect of statistical uncertainty per calculation(SUpC)of X-ray voxel Monte Carlo(XVMC)algorithm of Monaco radiotherapy plan system on the optimization and dose calculation of volumetric modulated arc therapy(VMAT)for rectal cancer.Methods:This study selected the radiotherapy data of 10 patients with rectal cancer at the First Affiliated Hospital of Guangxi Medical University retrospectively.In Monaco radiotherapy plan system,the XVMC algorithm was adopted,and the SUpC was respectively set as 0.25,0.50,0.75,1.00,1.25 and 1.50 to design 6 kinds of VMAT plans(SUpC0.25,SUpC0.50,SUpC0.75,SUpC1.00,SUpC1.25,SUpC1.50)for optimization and calculation.The differences of maximum dose(Dmax),mean dose(Dmean),homogeneity index(HI),conformity index(CI)of target regions among 6 kinds of VMAT plans were compared.The differences of the doses of bladder,small intestine and femoral head of organs at risk(OAR)and normal tissue among different VMAT plans also were compared.In addition,the effects of statistical uncertainty per control point(SUpCP),loss value(loss),history density(HD),time of optimization and calculation(Time),sub field(Segment),monitor unit(MU),delivery time(DT)on the optimization of VMAT plan were analyzed.Results:Compared with SUpCP0.25,the Dmax,Dmean and HI of other 5 kinds of target regions respectively increased,and CI of them respectively decreased with the increasing of SUpC,and the differences were significant(F=45.62,13.83,24.94,15.79,P<0.05),respectively.The Dmax and Dmean of OAR bladder,and the Dmax and V50 of normal tissue respectively increased,and the differences were significant(F=26.54,0.87,45.52,7.05,P<0.05).Compared with SUpCP0.25,the time of optimization and calculation(Time)of other 5 kinds of plans respectively decreased with the increasing of SUpC,and the difference was significant(F=329.69,P<0.05).When SUpC≤1,the dose deviation of target region Dmax was smaller or equal to 3%than SUpC0.25,and the time of optimization and calculation was<10 min.Conclusion:With the increasing of SUpC value,the Dmax of high dose region increases,and the dose of target dose is overestimated,and the HI and CI of target region are deterioration,and the efficiency of optimization and calculation is accelerated.For the Monaco plan system,the SUpC is 1 is recommended to use in designing VMAT plan for rectal cancer,which can effectively increase the optimal efficiency of VMAT plan of rectal cancer under ensuring the best quality of plan.It can provide theoretical basis for the design of clinical VMAT plan of rectal cancer.
X-ray voxel Monte Carlo(XVMC)Statistical uncertaintyRectal cancerVolumetric modulated arc therapy(VMAT)
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