Field matching in breast irradiation: An exact solution to a geometrical problem.

In radiation therapy of breast cancer several photon fields are used. Proper matching of the fields and minimizing the irradiated lung volume can be obtained by suitable beam blocking and appropriate angulation of the gantry, collimator and turntable. To facilitate the simulation procedure a new general method has been developed to calculate these angles, the position of the beam blocks and the field dimensions exactly.