Can we predict radiation-induced changes in pulmonary function based on the sum of predicted regional dysfunction?

Purpose: To determine whether changes in whole-lung pulmonary function test (PFT) values are related to the sum of predicted radiation therapy (RT)-induced changes in regional lung perfusion. Patients and Methods: Between 1991 and 1998, 96 patients (61% with lung cancer) who were receiving incidental partial lung irradiation were studied prospectively. The patients were assessed with pre- and post-RT PFTs (forced expiratory volume in one second [FEV1] and diffusion capacity for carbon monoxide [DLCO]) for at least a 6-month follow-up period, and patients were excluded if it was determined that intrathoracic recurrence had an impact on lung function. The maximal declines in PFT values were noted. A dose-response model based on RT-induced reduction in regional perfusion (function) was used to predict regional dysfunction. The predicted decline in pulmonary function was calculated as the weighted sum of the predicted regional injuries: [GRAPHICS] where V-d is the volume of lung irradiated to dose d,and R-d is the reduction in regional perfusion anticipated at dose d. Results: The relationship between the predicted and measured reduction in PFT values was significant for uncorrected DLCO (P =.005) and borderline significant for DLCO (P =.06) and FEV1 (P =.08). However, the correlation coefficients were small (range, .18 to .30). In patients with lung cancer, the correlation coefficients improved as the number of follow-up evaluations increased (range,.43 to .60), especially when patients with hypoperfusion in the lung adjacent to a central mediastinal/hilar thoracic mass were excluded (range, .59 to .91). Conclusion: The sum of predicted RT-induced changes in regional perfusion is related to RT-induced changes in pulmonary function. In many patients, however, the percentage of variation explained is small, which renders accurate predictions difficult. J Clin Oncol 19:543-550. (C) 2001 by American Society of Clinical Oncology.