Short-term pulmonary side-effects following radiation therapy in breast cancer

Abstract: The purpose of this dissertation was to study the short-term pulmonary sideeffects following adjuvant radiotherapy for breast cancer in terms of clinical pulmonary complications, loss of pulmonary function and radiological abnormalities, and the association to irradiated lung volume and dose. Furthermore, we wanted to estimate the influence of covariates, e.g. age, sequential chemotherapy, concurrent tamoxifen treatment, smoking habits, pretreatment functional level and premorbidity, on the early radiation-induced response of lung. Severe pulmonary complications, i.e. managed with corticosteroids, were diagnosed among 10 % of the patients who were treated with loco-regional radiotherapy including the internal mammary nodes (IMN). Age and reduced pre-treatment functional level were independently associated with pulmonary complications. The mean irradiated ipsilateral lung volume receiving more than 20 Gy was larger among the patients diagnosed with both clinical and radiological pneumonitis than in patients experiencing neither of the two side-effects. Severe pulmonary complications were very rare (<1%) among patients who were treated with local radiotherapy. A mean reduction in pulmonary function, i.e. vital capacity, was observed among patients treated with loco-regional radiotherapy including the IMN compared both to patients in whom the IMN were excluded from the target volume and to patients who were treated with local radiotherapy. The mean reduction in vital capacity among patients who were diagnosed with severe pulmonary complications was clinically significant and equivalent to the loss of 3/4 of a lung lobe. Furthermore, postirradiatory reduction in vital capacity was independently associated to only irradiated lung volume. The patients who were pre-treated with chemotherapy had lower mean diffusion capacity than expected, i.e. 78 % of predicted, at baseline and this was probably caused by drug-induced toxicity. Radiological abnormalities were most often seen among patients in whom large lung volumes had been included within the fields of irradiation. Postirradiatory radiological abnormalities were more frequently seen in older patients and were associated with both pulmonary complications and loss of vital capacity. Computerised tomography was found to be a more sensitive technique for diagnosing postirradiatory radiological abnormalities and was more strongly associated to functional end-points than chest radiography. In conclusion, loco-regional radiotherapy in breast cancer is associated with clinically significant short-term pulmonary side-effects. The results of this work also suggest that a more individualised treatment planning aimed at reducing the irradiated lung volume receiving more than 20 Gy may reduce the incidence of pulmonary side-effects in this group of patients.