Comparison of the effects of two typesof multileaf collimators on tumor control probabilityin radiotherapy for breast cancer after conservativesurgery based on the EUD model

Objective To compute and compare the tumor control probability （TCP） of volumetric modulated arctherapy （VMAT） for breast cancer after conservative surgery based on two types of multileaf collimator（MLC） through a retrospective planning study.Methods For a group of 9 patients diagnosed with left breast cancer, VMAT plan based on Agility MLCand beam modulator （BM） MLC were designed. The prescription dose was 50 Gy covering at least 95% ofthe planning target volume, 2 Gy per fraction. TCPs were calculated according to dose-volume histogram（DVH） analysis.Results The TCP of the BM VMAT plan was slightly higher than that of the Agility VMAT plan （94.61% vs94.23%） but was inferior with respect to delivery efficiency; the delivery time was reduced for Agility VMATplan by 35% compared to BM VMAT plan.Conclusion For breast cancer radiation therapy after conservative surgery, BM VMAT plans provideslightly higher TCP while the delivery of Agility VMAT plans is significantly faster than the BM VMAT plans.