4-Dimensional computed tomography-based ventilation and compliance images for quantification of radiation-induced changes in pulmonary function.

Abstract

4-Dimensional computed tomography (4DCT)-based ventilation imaging is a promising technique for evaluating pulmonary function, but lung elasticity and mechanics are usually not part of the ventilation image analysis. In this study we demonstrate a 4DCT-based imaging technique that can be used to calculate regional lung compliance changes after radiotherapy (RT). Six lung cancer patients were included in this study. Four of the patients had 4DCT images acquired pre-RT, 3 and 9months post-RT. Ventilation and compliance were calculated from the deformable image registration (DIR) of 4DCTs, performed from the end-inhale to the end-exhale breathing phase. Regional compliance was defined as the ratio of volumetric variation and associated stress in each voxel, representing lung elasticity and computed using a FEM-based framework. Ventilation, compliance and CT density were calculated for all pre-RT and post-RT 4DCTs and evaluation metrics were computed. Average CT density changes were 13.6±11.4HU after 3months and 26.9±15.8HU after 9months. Ventilation was reduced at 3months, but improved at 9months in regions with dose≥35Gy, encompassing about 10% of the lung volume; compliance was reduced at both time-points. Radiation dose≥35Gy caused major change in lung density and ventilation, which was higher than that previously reported in the literature (i.e. 24Gy). Lung tissue response is diverse with respect to CTdensity, ventilation and compliance. Combination of ventilation and compliance with CT density couldbe beneficial for understanding radiation-induced lung damage and consequently could help develop improved treatment protocols for lung cancer patients.