Prospective prediction of post-radiation therapy lung function using quantitative lung scans and pulmonary function testing.

Surgeons have made use of quantitative perfusion lung scanning (QS) and forced expiratory volume in one second (FEV1) to predict a patient's ability to tolerate lung resection. In this study QS and FEV1 were used to predict prospectively pulmonary function following lung irradiation (XRT). Twenty-two patients have had QS and FEV1 determined before XRT and at planned intervals post-XRT. Serial determination of lung function post-XRT allows comment on the temporal nature of the XRT effect on lung function. Seventeen patients had QS and FEV1 determined at an interval of 2-6 months post-irradiation with a drop in the groups mean FEV1 from 1.91 to 1.87L. or 2% during that interval. In the interval from 6-12 months post-XRT, 13 patients had studies with the groups mean FEV1 dropping from 1.79 to 1.58L or 12% of the original. In the interval from 12-18 months, 6 patients had a decline in mean FEV1 from 1.73 to 1.56L. or 10% of the original. In 22 patients a predicted final FEV1 was compared with a measured value at an interval from XRT. Fourteen of these determinations were at intervals greater than 6 months from the start of XRT and 6 at intervals of greater than 1 year. FEV1 was seen to drop during the follow-up intervals toward the predicted value. In only 2 patients did the final FEV1 drop below the predicted FEV1 and never by more than 0.12L. (6%). In summary, a method for predicting post-XRT pulmonary function using QS and FEV1 is described. Serial follow-up revealed a latent period followed by a late phase where FEV1 fell toward, but not significantly below, the predicted value. Such a determination can be of value in formulating a treatment plan for patients with significantly diminished pulmonary function.