Lung dose analysis in loco-regional hypofractionated radiotherapy of breast cancer

OBJECTIVES: To report the ipsilateral lung dosimetry data of breast cancer (BC) patients treated with loco-regional hypofractionated radiotherapy (HFRT). METHODS: Treatment plans of 150 patients treated in the Radiotherapy Unit, King Abdulaziz University Hospital, Jeddah, Kingdom of Saudi Arabia between January 2012 and March 2015 by HFRT for BC were retrospectively reviewed. All patients received 42.4 Gy in 16 fractions by tangential and supra-clavicular fields with 6 MV, 18 MV, or mixed energies. Ipsilateral lung dosimetric data V(20Gy) and mean lung dose (MLD) were recorded. Correlations between lung dose, patient characteristics, and treatment delivery parameters were assessed by a logistic regression test. RESULTS: The mean ipsilateral lung V(20Gy) was 24.6% and mean MLD was 11.9 Gy. A weak, but statistically significant correlation was found between lung dose and lung volume (p=0.043). The lung dose was significantly decreasing with patient separation and depth of axillary lymph node (ALN) and supra-claviculary lymph nodes (SCLN) (p<0.0001), and increasing with ALN (p=0.001) and SCLN (p=0.003) dose coverage. Lung dose significantly decreased with beam energy (p<0.0001): mean V(20Gy) was 27.8%, 25.4% for 6 MV, mixed energy, and 21.2% for 18 MV. The use of a low breast-board angle correlates with low lung dose. CONCLUSION: Our data suggest that the use of high energy photon beams and low breast-board angulation can reduce the lung dose.