CT Analysis of Lung Density Changes in Patients Undergoing Total Body Irradiation Prior to Bone Marrow Transplantation

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Abstract
Sequential changes in lung density measured by CT [computed tomography] are potentially sensitive and convenient monitors of lung abnormalities following total body irradiation (TBI). Methods were developed to compare pre- and post-TBI CT of lung. The average local features of a cross-sectional lung slice are extracted from 3 peripheral regions of interest in the anterior, posterior and lateral portions of the CT image. Also, density profiles across a specific region may be obtained. These may be compared first for verification of patient position and breathing status and then for changes between pre- and post-TBI. These may also be compared with radiation dose profiles through the lung. A preliminary study on 21 leukemia patients undergoing total body irradiation indicates the following: Density gradients of patients'' lungs in the antero-posterior direction show a marked heterogeneity before and after transplantation compared with normal lungs. The patients with departures from normal density gradients pre-TBI correlate with later pulmonary complications. Measurements of average peripheral lung densities have demonstrated that the average lung density in the younger age group is substantially higher: pre-TBI, the average CT number (1000 scale) is -638 .+-. 39 Hounsfield unit (HU) for 0-10 yr old and -739 .+-. 53 HU for 21-40 yr old. Density profiles showed no post-TBI regional changes in lung density corresponding to the dose profile across the lung, so no differentiation of a radiation-specific effect has yet been possible. CT density profiles in the antero-posterior direction are successfully used to verify positioning of the CT slice and the breathing level of the lung.