Report of a workshop: quantitative computed tomography scanning in longitudinal studies of emphysema.

It has been reported that quantitative computed tomography (CT) scanning of the lungs showed decreased progression of emphysema in a randomised clinical trial in patients with severe alpha1-antitrypsin (alpha1-AT) deficiency receiving monthly intravenous augmentation therapy with human alpha1-AT. Comparable results were not obtained using rate of decline of forced expiratory volume in one second. Accordingly, the Alpha-1 Foundation convened a workshop to explore the feasibility of using quantitative CT data as a primary outcome variable in trials of drugs for treating alpha1-AT deficiency. This report reviews the following: the principles for the use of modern CT scanners for quantifying emphysema; the methods and data on validation by comparison with measurements of severity of emphysema in inflation-fixed specimens of lungs; and the possibility of decreasing radiation dosage from CT to make it safe and ethically possible to use CT in longitudinal studies. The workshop concluded that it is feasible, safe and ethically possible to use computed tomography in longitudinal studies of emphysema. It recommended that the primary end-point should be a significant shift in the 15th percentile of lung density.