Is radiation treatment volume a predictor for acute or late effect on pulmonary function? A prospective study of patients treated with breast-conserving surgery and postoperative irradiation

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Abstract
When tangential radiation beams are used in patients with breast cancer after breast-conserving surgery, the amount of lung included in the radiation field varies because of patient anatomy and treatment technique. The question of how much lung tissue can be irradiated incidentally without acute or late complications requires quantitative study. Thirty-four women were enrolled in a prospective study of pulmonary function after breast-conserving surgery and radiotherapy for early stage breast cancer. The percentage of lung volume irradiated was estimated from computed tomography scans. Pulmonary function tests including spirometrics, lung volume, and diffusing capacity of carbon monoxide (DLCO) were performed before, during, and at regular intervals after radiotherapy. Both acute and long term changes in pulmonary function were analyzed in 29 eligible patients. Acutely, DLCO values dropped, but they returned to normal levels by 24 months. At 5 years, pulmonary function did not vary significantly according to the percentage of lung irradiated, the use of regional lymphatic irradiation, or the addition of chemotherapy. Symptomatic pneumonitis occurred only in two women with baseline deficits in DLCO (P = 0.016), who had more than 10% of the total lung volume irradiated. Patients with a smoking history had a clinically significant baseline deficit of 32% in DLCO values (P = 0.0011) but showed a 21% improvement (P = 0.11), which probably correlated with quitting smoking. Within the range evaluated in this study, the volume of lung irradiated did not predict a late decrease in pulmonary function, although pneumonitis was observed only when more than 10% of the lung was irradiated.

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