Dependence of the degree of radiation damage lung tissue on the localization of the irradiated volume according to quantitative analysis of CT

Objective. Study of the radiosensitivity of various areas of lung tissue by quantifying changes in its density as a result of therapeutic irradiation using computed tomography data. Materials and methods. We used data from a dynamic observation of 90 patients who underwent RT for chest tumors from 2014 to 2021 at the Federal State Budgetary Institution "Russian Scientific Center of Rentgenoradiology" (RSCRR). Among the patients there were 36 (40.0%) men and 54 (60.0%) women aged from 23 to 86 years (mean age was 51.9±15.6 years). All these patients underwent computed tomography before and after RT. Control studies were carried out 1-237 days after RT (mean control interval 96±64.3 days). A total of 238 CT examinations were analyzed, with an average number of CT examinations per patient of 2.6. The values of mean density change in Hounsfield units (HUav), median density change (Δm HU), and statistical deviation (Sd) were calculated for lung tissue in volumes irradiated in specified isodose ranges with parallel determination of the values of these volumes. The method of quantitative analysis of lung tissue density according to CT studies was described in detail by us earlier. Results. The maximum values of early changes (Δm HU) in the lungs were 86±234 HU, and late ones - 62±194 HU. From the point of view of searching for the causes of heterogeneity, patients were divided into groups. The first group was characterized by the location of the irradiated volume in the peripheral areas of one of the lungs - 50 patients (82 investigations) with various clinical diagnoses after RT with a total focal dose (TFD) from 24 Gy to 84 Gy-eq. (average dose 50±12.6 Gy). Moreover, in early (up to 120 days after RT) 45 investigations, reliable Δm HU in these patients ranged from 27 HU to 932 HU (with a median of 168±264 HU, p=0.058), and in late (from 120 days – 38 investigations) - from 30 HU to 814 HU (with a median of 143±204 HU, p=0.056). The first group included 28 patients with breast cancer and 2 patients with malignant lymphoma (early Δm HU - from 27 HU to 793 HU and late - from 30 HU to 529 HU), as well as 20 patients with lung cancer (early Δm HU - from 35 HU to 932 HU, late - from 26 HU to 814 HU). The second group was characterized by the location of the irradiated volume in the mediastinum and adjacent central areas of the lungs - 40 patients (73 investigations) with various clinical diagnoses with an TFD from 15 Gy to 66 Gy-eq. (median 32±12 years). At the same time, early Δm HU in these patients varied from 16 HU to 385 HU (with a median of 50±62 HU, p=0.041), and late ones - from 18 HU to 312 HU (with a median of 41±66 HU, p=0.043). The second group included: 5 patients with lung cancer who underwent postoperative RT (Δm HU early - from 49 HU to 96 HU, late - from 35 HU to 60 HU), 8 patients with thymomas (Δm HU early - from 20 HU to 385 HU, late - from 30 HU to 312 HU) and 27 patients with malignant neoplasms of mediastinal lymphoma (Δm HU early - from 16 HU to 112 HU, late - from 18 HU to 81 HU). In both groups, 18 patients were identified with Δm HU values significantly different from the Δm HU values of the remaining patients in the respective groups, which may indicate their abnormal radiosensitivity. Conclusions. Quantitative analysis of CT data did not reveal any dependence of changes in the median density of lung tissue (Δm HU) on the inclusion of different areas of lung tissue in the irradiated volume and, therefore, the radiosensitivity of peripheral and central areas of the lungs is the same. The value of Δm HU in lung tissue depends on the total absorbed dose, but the magnitude of this dependence is individual and is also due to variability in radiosensitivity in cancer patients.