Session Item

This study aimed to analyse the correlation between contralateral breast (CLB) exposure and patient’s specific anatomic parameters in breast cancer radiotherapy and to investigate whether these parameters could reliably predict doses to CLB.

Data of 150 patients planned for adjuvant 3D conformal breast cancer radiotherapy were evaluated. Radiotherapy was delivered by tangential fields +/- supraclavicular field, using a mono-isocentric technique and a hypofractionated schedule (40 Gy delivered in 15 daily fractions +/- an additional boost of 13.35 Gy). The CLB was contoured based on the ESTRO guidelines. For each patient, the following anatomic features were assessed: CLB volume (cc), breast height measured at the sagittal plane, central breast to breast distance (CBB) calculated as the minimum distance between the contoured breasts at the central axial slice. Dose-volume histograms were generated and the following dosimetric parameters were calculated: Dmean, Dmax and V4 Gy to CLB. Statistical associations between patient’s anatomic features and dosimetric parameters to CLB were analysed using Pearson correlation and linear regression.

Mean age was 46 (28-71) years. Eighty-six percent of patients underwent regional lymph nodes irradiation. The mean Dmax/Dmean to CLB was 10.12 Gy/0.78 Gy. The mean V4 Gy to CBL was 0.99% ranging between 0.02% and 8.77%. Substantial interpatient variability in CLB exposure was noticed with Dmax/Dmean ranging between 0.51 Gy/0.18 Gy and 40.12 Gy/2.79 Gy. The CBB distance largely varied in this cohort from 2 cm to 13.35 cm with a mean value of 4.77 cm. The CBB distance was strongly correlated to Dmean and V4 Gy to CLB, with Pearson coefficients of 0.53 and 0.5 (p<0.001), respectively. For every 1 cm increase in CBB distance, Dmean to CLB decreased by 41%. No statistical association was found between CBB distance and Dmax to CLB. Neither CLB volume nor CLB height were statistically correlated to CLB doses

This study showed that CBB distance is a reliable predictor of CLB exposure in 3D conformal breast cancer radiotherapy. Personalized estimation of CLB doses from planning CT data allows early patient’s selection for CLB sparing radiotherapy techniques, especially in patients with high risk of contralateral breast cancer.