Simple geometrical models used by Dance (1990) (a,b), Wu et al (1991) (a,b) and Boone (1999) (a,c) to model the breast in the CC projection. All three models have a central region which is a homogeneous mixture of adipose and glandular tissues surrounded by an outer layer. In the Dance model this layer is adipose tissue whereas in the other two models it is skin. In the Dance model the breast is a cylinder of semi-circular cross section, whereas in the Wu model it has semi-elliptical cross section. The Boone model (a, c) uses a phantom of circular cross section, only half of which is irradiated (the thick line shows the position of the radiation field.