Background: Depending on the lung volume in radiotherapy fields, breast cancer radiotherapy has documented side effects on pulmonary function, which can be determined by pulmonary function tests. Central lung distance (CLD), the distance from the chest wall to the edge of the field at the central axis, is an indicator of lung volume within the radiotherapy fields. In this study, we aim to detect the relationship between CLD and pulmonary function tests.

Methods: In this study we included 50 patients with breast cancer receiving postoperative adjuvant radiotherapy at Imam Hossein Hospital, Tehran, Iran. The patients received radiotherapy with a total dose of 4800-5000 cGy. For all patients, the central lung distances were measured using simulation of tangential fields, in addition to determination of pulmonary function, including force vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) determined before radiotherapy, one month and three months after radiotherapy.

Results: There is no significant statistical difference between the FEV1 and FVC values before radiotherapy and those measured one month after radiotherapy; however there was a significant statistical decrease in the FEV1 and FVC before radiotherapy and those measured three months after radiotherapy (P<0.001 and P<0.006, respectively). There is a positive statistical correlation between the change in the FEV1 three months after therapy and the CLD (r=0.71, p<0.01) and that of the FVC three months after therapy and the CLD (r=0.59, p<0.01). Linear regression for the prediction of FEV1 and FVC three months after radiotherapy was designed according to the CLD, FEV1 and FVC values before radiotherapy.

Conclusions: Three months after breast radiotherapy, the FEV1 and FVC values decrease, and the CLD is a proper predictor of these changes.