Invited review: tangential breast irradiation--rationale and methods for improving dosimetry.

In recent years there have been great advances and innovations in all technical aspects of radiotherapy, including three dimensional (3D) computer planning, patient immobilization, radiation delivery and treatment verification. Despite this progress, the technique of tangential breast irradiation has changed little over this period and has not exploited these advances. There is increasing evidence that dose inhomogeneity within the breast is greater than at other anatomical sites, especially in women with large breasts. This paper is a review of the factors contributing to poor dosimetry in the breast, the clinical consequences of an inhomogeneous dose distribution, and how breast dosimetry could be improved by considering each of the stages from planning to accurate treatment delivery. It also highlights the particular problem of women with large breasts who may be more likely to have a poorer cosmetic outcome after a fractionated course of radiotherapy than women with small/medium-sized breasts, and supports the clinical impression that such women are also more likely to have greater dose inhomogeneity when 3D treatment plans are examined. Preliminary data from our current computed tomography (CT) planning study are presented to support these observations.