Modern Hypofractionation Schedules for Tangential Whole Breast Irradiation Decrease the Fraction Size-corrected Dose to the Heart

Aims: Hypofractionation of postoperative radiotherapy for breast cancer has been evaluated in a number of large randomised clinical trials, but concerns remain over the late cardiac toxicity. In this study, we examined the predictions of the linear quadratic model on the estimated fraction size-corrected dose to the heart for four evidence-based hypofractionation regimens. Materials and methods: Dose plans for 60 left-sided breast cancer patients were analysed. All patients were planned with tangential fields for whole breast irradiation. Dose distributions were corrected to the equivalent dose in 2 Gy fractions (EQD(2)) using the linear quadratic model for five different fractionation schedules (50 Gy/25 fractions and four hypofractionation regimens) and for a range of alpha/beta. values (0-5 Gy). The mean EQD(2) to the heart (D-mean(EQD2)) and the volume receiving 40 Gy (V-40(Gy)EQD2), both as calculated from the EQD(2) dose distributions, were compared between schedules. Results: For alpha/beta = 3 Gy, V-40(Gy)EQD2 favours hypofractionation for 40 Gy/15 fractions, 39 Gy/13 fractions and 42.5 Gy/16 fractions, but not for 41.6 Gy/13 fractions. All of the hypofractionation schedules result in lower D-mean(EQD2) compared with normofractionation. These results hold as long as alpha/beta greater than or similar to 1.5 Gy. If the heart is blocked from the treatment beam, the fraction size-corrected dose is lower for the first three hypofractionation schedules, compared with normofractionation, even for alpha/beta = similar to 1 Gy. Conclusion: For standard tangential field whole breast irradiation, most of the examined hypofractionation schedules are estimated to spare the heart when compared with normofractionation. The dose to the heart, adjusted for fraction size using the linear quadratic model, will generally be lower after hypofractionated compared with normofractionated schedules, even for very low values of alpha/beta. (C) 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.