The Dosimetric effects of Monte Carlo Variance and Fluence Smoothing on VMAT Radiotherapy Plans for Breast Cancer
Objective To investigate the effects of physical characteristics with different combinations of Monte Carlo variance(MCV)and fluence smoothing factor(FSF)on Volumetric Modulated Arc Therapy(VMAT)dosimetry and radiobiological parameters in VMAT,and to optimize the radiotherapy plan.Methods With the selection of 12 patients with left breast cancer who underwent VMAT radiotherapy plan design in the hospital from January 2021 to December 2022 as the research objects,by selecting different MCV options(0.5%,1%,2%)in Monaco 5.11 TPS to adjust the dose calculation error range,and by by adjusting FSF(Low,Medium,High)to reduce noise in intensity distribution maps,nine radiotherapy plans were designed for each patient,including Low 0.5,Low 1.0,Low 2.0,Medium 0.5,Medium 1.0,Medium 2.0,High 0.5,High 1.0,and High 2.0,totaling 108 radiotherapy plans.The system default parameters(MCV=1%,FSF=Medium 1.0)were used as the control group,while the rest were included in the experimental group.The dosimetric parameters of the patient's target area and organs at risk were evaluated using dose-volume histograms(DVH).Meanwhile,physical parameters such as the number of segments,machine units(MU),and treatment time(T)were recorded.Results Among 108 radiotherapy plans,77.7%of the plans met the PTV constraint of covering 95%of the target volume with 95%of the prescribed dose,and more than 90%of the target volume received 95%of the prescribed dose in the remaining plans.The dose to 2%PTV(D2%),mean dose(Dmean),conformity index(CI)and homogeneity index(HI)of all experimental groups were significantly different from those of the control group(P<0.05).In terms of dosimetric parameters of the heart,affected lung,and healthy breast,changes in MCV values had a relatively small impact on dose,while changes in FSF values had a significant impact on dosimetry and physical parameters,with statistical significance(P<0.05).Conclusions With the design of the VMAT treatment plan for patients with left breast cancer after surgery,by properly adjusting the MCV value and FSF,the radiotherapy plan can be optimized,the segments and T can be reduced,while maintaining the dose coverage,so as to improve the treatment efficiency and quality.It was recommended to use MCV of 1%and FSF as a combination of Low and Medium to obtain better dosimetry and biological effects.
Monte CarloVMATDosimetryFluence smoothingBreast cancev
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