Radiation-induced fibrosis in the boost area after three-dimensional conformal radiotherapy with a simultaneous integrated boost technique for early-stage breast cancer: A multivariable prediction model

Background and purpose: To develop a multivariable prediction model for the risk of grade >= 2 fibrosis in the boost area after breast conserving surgery (BCS) followed by three-dimensional conformal radiotherapy (RT) with a simultaneous integrated photon boost (3D-CRT-SIB), five years after RT. Material and methods: This prospective cohort study included 1,030 patients treated with RT for breast cancer (stage 0-III), after BCS. Data regarding physician-rated fibrosis and dose-volume parameters were available in 546 patients. A multivariable logistic regression model for grade >= 2 fibrosis was generated. Results: At 5 years, grade >= 2 fibrosis was observed in 13.4% of the patients. The multivariable analysis resulted in a prediction model for grade a >= 2 fibrosis in the boost area including three independent variables: patient age, breast volume receiving >= 55 Gy (V55 CTV breast) and the maximum radiation dose in the breast (D-max). Conclusions: A multivariable prediction model was developed including age, V55 CTV breast and D-max for grade >= 2 fibrosis in the boost area after breast cancer RT using a 3D-CRT-SIB technique. This model can be used to estimate the risk of fibrosis and to optimize dose distributions aiming at reducing this risk. (C) 2016 Elsevier Ireland Ltd. All rights reserved