Physics of Hypofractionated Whole Breast Irradiation

Abstract

Whole breast irradiation (WBI) is routinely used in the management of early-stage breast cancer, when coordinated with lumpectomy along with a possible chemotherapy regimen. The conventional WBI fractionation scheme is 2 Gy per fraction. Several WBI fractionation schemes, including hypofractionated WBI (HWBI), have been investigated. HWBI offers advantages to the patient such as reduced out-of-pocket costs as well as to radiation oncology departments such as the ability to schedule and treat more patients per year on a given linear accelerator. The higher dose per fraction for HWBI compared with conventional WBI has some consequences with regard to how a conventional megavoltage linear accelerator will be applied for treatment. Generally, HWBI requires better control of the patient’s motion during delivery. The reduced number of fractions in HWBI requires more precise and accurate patient positioning. Image-guided radiation therapy (IGRT) may be useful. Other physics-related issues specific to HWBI include the need of 3D imaging-based conformal treatment planning, the changes of normal tissue dose-volume constraints for treatment planning, and the radiobiology consideration in the fractionation schemes. The rationale and considerations of these issues are presented in this chapter.