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Breast cancer radiotherapy has been recently related to higher risk of subsequent oesophageal cancer in long-term survivors. The aim of this study was to assess radiation oesophagus exposure in modern hypofractionated 3D conformal breast cancer radiotherapy.

Data of 436 women planned for adjuvant hypofractionated 3D conformal radiotherapy were evaluated. Patients were treated in the years 2019-2020. The prescription dose was 40 Gy delivered in 15 daily fractions of 2.67 Gy +/- an additional boost of 13.35 Gy to the tumor bed. Patients were treated with tangential fields +/- supraclavicular field. Oesophagus was contoured according to the RTOG guidelines. Dose volumes histograms were generated for all delineated structures. Mean and maximum doses, V5 Gy, V10 Gy and V20 Gy to oesophagus were assessed and analysed with regards to irradiated target volumes.

The mean Dmean /Dmax to oesophagus was 2.6 Gy/20.57 Gy. The average V5 Gy, V10 Gy and V20 Gy were respectively 9.8%, 3.93%, 0.31%. Oesophagus exposure was strongly correlated to nodal radiotherapy with Pearson coefficient of 0.78 (p<0.01). For breast or chest wall radiotherapy, the mean Dmean/Dmax was 0.37 Gy/0.53 Gy, versus 9.3 Gy/26.7 Gy for radiotherapy including sub clavicular nodes. The V10 Gy to oesophagus was > 35% for 67% of patients receiving sub-clavicular nodal irradiation. For radiotherapy including axillary lymph nodes, doses to oesophagus were substantially higher with average Dmean/Dmax of 10.2 Gy/29.4 Gy.

This study showed higher oesophagus exposure in radiotherapy including sub-clavicular nodes when compared to breast/chest wall radiotherapy alone. The mean Dmean oesophagus was 9.3 Gy in sub-clavicular nodal radiotherapy, which may increase threefold the risk of oesophageal cancer according to recent evidence. Therefore, oesophagus contouring and sparing should be routinely considered in nodal radiotherapy planning as it may substantially reduce the risk of radiation induced oesophageal cancer.