Geometric factor analysis for dose distribution in the whole breast irradiation

Background Protecting the heart and left lung is important for left-sided breast cancer radiotherapy. So，this study was to investigate the effect of geometric parameters on the dose of left lung and heart in whole breast radiotherapy. Methods A plan was designed for each patient using VMAT technology for thirty patients. A triangular ABC of the target was defined layer by layer. The geometric parameters were defined: Rat-H (the ratio of heart), Rat-L (the ratio of lung), the curvature and thickness of the target ρ and d . Explored the relationships between these parameters and the dose-volume of heart (V 5,h , V 10,h , V 20,h , MHD) and left lung (V 5,LL , V 10,LL , V 20,LL , V 30,LL , V 40,LL , MLD). Results The V 5,h , V 10,h and MHD were all significantly associated with Rat-H (p<0.05). The V 5,LL , V 10,LL , V 20,LL , V 30,LL , V 40,LL and MLD were all significantly associated with Rat-L (p<0.05). And the V 20,LL , V 30,LL and V 40,LL were all significantly associated with d (p<0.05). Meanwhile，V 30,LL and V 40,LL were all significantly associated with ρ (p<0.05) . The correlations of the dose-volume of left lung and the four geometric parameters could be expressed by linear functions. Conclusions The geometric parameters Rat-H, Rat-L, d and ρ were closely related to the dose-volume of heart and left lung in whole breast radiotherapy.