Risks of lung fibrosis and pneumonitis after postmastectomy electron radiotherapy.

Breast cancer patients are treated by a variety of options. Electron beams are utilised in the irradiation of the chest wall postmastectomy due to its dose distribution in the irradiated body. The objectives of this study were to determine the possibility of inducing lung fibrosis and pneumonitis during postmastectomy radiotherapy (PMRT) using electron beams. Electron beams with different energies and gantry angles were used for irradiating the chest wall in PMRT. The normal-tissue-complications-probability of the lung was evaluated. Three computer codes EGSnrc, XTING and DORES were used for simulating the beams and patients, generating dose-volume histograms and evaluating the dose response of the lung. NTCP increases with energy and with gantry angle. Below 15 MeV (which had given very high and unacceptable NTCP values), the largest value of NTCP of fibrosis was 0.036, for 12 MeV, gantry angle 60. The largest value of NTCP of radiation-induced pneumonitis was 0.044, for 12 MeV, gantry angle 60.