A new Method of Quantitative Estimation of Radiation-Induced Lung Damage in Oncological Patients on the CT in Dynamics

Objective: to develop a methodology for quantitative assessment of changes in density parameters of pulmonary tissue on the basis of dynamic CT data, which makes it possible to assess the presence of the dependence of changes in lung tissue on the time elapsed after radiation therapy (RT), the dose and volume of irradiated pulmonary tissue.Materials and methods. Using the data collected by 11 patients with malignant lymphomas, we developed a new diagnostic technique for quantitative analysis, which is based on the analysis of the density of pulmonary tissue before and after RT in areas with a selected range of doses throughout the lung volume. All selected patients received LT in the chest region, using 3D-planning, fractions of 2Gy and total focal doses of 13–56 Gy. Also, each patient had at least two CT examinations (a total of 25 studies in the Dicom- format). The first CT scan was performed before LT, repeated – within 2–7 months after the end of RT.Results. In 6 patients, control CT examinations were performed 2.1–2.8 months after RT. As a result, a quantitative increase in the density indices in the range from +12 to +62 HU in regions of the lungs irradiated at a dose of more than 19 Gy was noted, different from the control areas. The volume of these areas of the lungs was from 16% to 30% of the total lung volume, and the volume of regions with the maximum values of density growth – from 7% to 14%. These changes in density are below the “visual” threshold. In control areas, the density change varied from −15 HU (increased airiness) to + 8 HU. According to the data of other CT studies performed later than 3 months after RT, the reverse development of changes characterizing the early radiation reaction was observed.Conclusions. A series of CT studies performed before and at various intervals after RT allows quantitative assessment of the dynamics of the indices of the density of irradiated pulmonary tissue, which is necessary for an objective assessment of the severity of early radiation-induced injuries of pulmonary tissue sites, depending on the dose. A study of the dynamics of these changes in pulmonary tissue density over time with RT and the connection of this indicator with the baseline data may allow one to predict radiation-induced damage to the lungs on the one hand, and on the other, to evaluate individual radiosensitivity.