The results of quantitative evaluation of postradiation changes in lung cancer patients, which were obtained using a new procedure for analysis of dynamic X-ray computed tomography imaging of thoracic organs

Objective: to reveal a relationship of lung changes to time after radiotherapy (RT), its dose, and irradiated volume, by using a new procedure to quantitatively evaluate lung tissue density changes according to the data of dynamic X-ray computed tomography (X-ray CT) imaging.Subjects and methods. Data on 29 cancer patients who had received RT to the chest area using 3D planning, 2-5-Gy fractions, and a total focal RT dose of 16 to 84 Gy in the lung tissue were retrospectively selected. Each patient underwent at least two X-ray CT studies (before and after RT); a total of 83 studies were analyzed. The new diagnostic procedure developed by the authors was used to quantitatively analyze lung tissue density changes in the areas with a selected dose range.Results. On days 1 to 15-30 after completion of RT, the quantitative analysis revealed no significant density changes. On days 70-80, there was an increase in changes that were different from those in the nonirradiated areas. On 80 to 100-120 days, there was a decline of radiation reactions with preserved changes in the areas irradiated at a dose of 19-20 Gy. From 120 days onwards, the changes were preserved in the areas irradiated at a dose of over 32-37 Gy through the formation of post-radiation pulmonary fibrosis. In addition, eight (27.6%) patients treated with less than 20 Gy were detected to have changes associated with the initial density values, which can be regarded as an increased individual radiosensitivity.Conclusion. The time course of a quantitative change in the median lung tissue density in the areas irradiated at different doses allows radiation-induced lung injury to be detected at X-ray CT until the visual signs of pneumonitis appear. A continuous, quantitative scale of changes will assist in more reliably and accurately studying post-radiation changes at a later time, and the time course of spaciotemporal changes will be able to compare and quantify lung injury when exploring new treatment methods and policies.