IS RADIATION TREATMENT VOLUME A PREDICTOR FOR ACUTE OR LATE EFFECT ONPULMONARY-FUNCTION - A PROSPECTIVE-STUDY OF PATIENTS TREATED WITH BREAST-CONSERVING SURGERY AND POSTOPERATIVE IRRADIATION

Background. When tangential radiation beams ire used in patients with breast cancer after breast-conserving surgery, the amount of lung incl uded in the radiation field varies because of patient anatomy and trea tment technique. The question of how much lung tissue can be irradiate d incidentally without acute oi late complications requires quantitati ve study. Methods. Thirty-four women were enrolled in a prospective st udy of pulmonary function after breast-conserving surgery and radiothe rapy far early stage breast cancer. The percentage of lung volume irra diated was estimated from computed tomography scans. Pulmonary functio n 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 pulm onary function were analyzed in 29 eligible patients. Results. Acutely , DLCO values dropped,but they returned to normal levels by 24 months, At 5 years; pulmonary function did not vary significantly according-t o the percentage, of lung irradiated, the use of regional lymphatic ir radiation, or the addition of chemotherapy. Symptomatic pneumonitis oc curred only in two women with baseline deficits in DLCO (P = 0.016), w ho had more than 10% of the total lung volume irradiated. Patients wit h a smoking history had a clinically significant baseline deficit Of 3 2% in DLCO value (P = 0.0011) but showed a 2l% improvement (P = 0.11), which probably dot related with quitting smoking. Conclusion. Within the range evaluated in this study, the volume of lung irradiated:did n ot predict;a late decrease In pulmonary function, although pneumonitis was observed only when more than 10% of the lung was irradiated.