Quantitative lung scans for prediction of post-radiotherapy pulmonary function.

Quantitative perfusion scans were used to predict the proportion of pulmonary function lost by inclusion of lung in radiotherapy fields. Nineteen patients receiving radiotherapy for carcinoma of the lung had pulmonary function evaluated by forced expiratory volume at 1 second (FEV1) prior to and following radiotherapy. FEV1 measurement followed initiation of radiotherapy from two to 18 months (mean: seven months). Prior to radiotherapy quantitative lung scans were performed with Tc-99m macroaggregated albumin. On images acquired by computer, the radiotherapy field was drawn as a region of interest (ROI) and the proportion of count within this ROI relative to total lung count was determined. The total FEV1 was apportioned by the ROI ratio of count excluded from radiation ROI to total count in lungs to predict the FEV1 expected to be remaining after radiotherapy. In only two cases was the measured post-therapy FEV1 less than predicted (and then, by only 2% and 5%, respectively). The data indicate that quantitative perfusion lung scans can be used to predict conservatively the pulmonary function that may be expected to remain post-radiotherapy. Therapy fields may be adjusted in patients with underlying compromised pulmonary function to conserve a pre-selected FEV1.