Intestine radiation damage: causes

Radiation disease or radiation damage to a number of organs, including the intestine, develops with the use of nuclear weapons (the tragedy in Hiroshima and Nagasaki in 1945), violation of safety rules and negligence with sources of ionizing radiation (events at the Chernobyl nuclear power plant), irrational the appointment of large doses of radiation therapy. With local irradiation of the abdominal and pelvic organs, the total dose of which exceeds 40 Gy (4000 rad), pathological changes can develop, mainly in the intestine. Most often, the defeat of the small and large intestine is combined, although there is often an isolated process in one of these parts of the intestine.

The first clinical report on bowel damage after radiotherapy of malignant neoplasm was made in 1917 by K. Franz and J. Orth. As the scope of radiotherapy has expanded, the number of reports of its complications has increased. In particular, it was noted that irradiation of various pelvic, intraperitoneal and retroperitoneal neoplasms leads to the appearance of radiation enteritis and colitis in 5-15% of patients. According to D. L Earnest, JSTrier (1983), radiation damage to the gastrointestinal tract continues to be one of the main and serious clinical problems.

The mechanism of the appearance of intestinal injuries under the action of ionizing radiation is primarily its effect on the epithelium of the mucous membrane, which is very sensitive to radiation exposure. Irradiation promotes suppression of cell proliferation in crypts, which causes characteristic acute disorders. If the radiation dose is low, the proliferation of epithelial cells is restored fairly quickly, and mucosal damage disappears 1-2 weeks after irradiation. The effect of repeated doses of radiation depends on the duration of irradiation and the stage of cellular renewal of the crypt epithelium. It has been established that the epithelial cells are particularly radiosensitive in the G1-postmitotic phase and resistant to the late S-synthetic phase. To restore the regeneration of the epithelium of the intestinal mucosa during fractional irradiation, the duration of the intervals between exposures is of great importance.

As can be seen, the development of acute and chronic changes inherent in radiation enteritis is affected not only by the total dose of irradiation and the method of its use, but also by the time between the courses of therapy.

Radiation therapy before and most often affects the epithelium. It also has an effect on mesenchymal tissue, which is most important in the occurrence of long-term effects. For example, the endothelium of the small intestine submucosal arterioles is very sensitive to the effects of ionizing radiation and reacts to large doses by proliferation. Vascular disorders appear after 1 week or 1 month after acute damage to the mucosa. The wall of the vessels undergoes fibrinoid changes, which further facilitates the thrombosis of the vessels. Develop obliterating endarteritis, endophlebitis, leading to ischemic disorders of the intestinal wall, followed by ulceration and necrosis. It worsens the patient's condition and aggravates the damage to the intestinal wall by introducing bacteria into the necrotic tissue, which increases as the blood supply deteriorates.

After massive irradiation, the gut becomes swollen; activation of fibroblasts is noted, connective tissue undergoes hyalinosis, in the development of which smooth muscle cells participate. As a result, extensive fibrosis is formed, which can lead to intestinal narrowing, as well as destruction of the mucosal surface. Consequently, ionizing radiation can cause both transient changes in the structure of the mucosa and bowel function, as well as thickening, ulceration, and intestinal fibrosis.

In addition to acute and chronic changes in it, subacute and latent are distinguished. Acute - occur immediately after irradiation, accompanied by a violation of proliferation and maturation of the epithelium in combination with a decrease in the mitosis of crypt cells. In the small intestine, characteristic shortening of the villi and a decrease in the thickness of the mucosa, as well as its hyperemia, edema and extensive inflammatory cell infiltration are observed. Crypt abscesses that contain neutrophils, eosinophils, and deleted epithelial cells are possible. With prolonged or massive irradiation, ulceration may occur.

Subacute changes appear 2 to 12 months after radiation therapy. They are very diverse. During this period, the endothelial cells of the small intestine arterioles in the submucosa can swell, flake off the basal membrane and eventually undergo necrosis. In the lumen of the vessel, thrombi are detected, in some cases, their recanalization. In the intima, large foam cells are found, which, according to some researchers, are considered to be an important diagnostic sign of radiation damage to blood vessels in humans. The submucosal layer becomes thickened, sclerosed, often contains large, irregularly shaped fibroblasts. The result of obliterating changes in small arterioles is progressive ischemia. The degree of vascular lesions and ischemic fibrosis is different and not always pronounced, therefore in the subacute the blood circulation in the intestine is often not significantly disturbed, except when the irradiation was preceded by diseases that affected the vessels (hypertension, diabetes, generalized atherosclerosis or coronary and heart failure ). Insufficiency of microcirculation due to radial vasculitis, representing the greatest danger, often occurs in the sigmoid and rectum. In the tissues that connect the large intestine with the vagina, bladder, ileum, abscesses and fistulas can form. Gut carcinoma is a late and relatively rare manifestation of its radiation damage.

[1], [2], [3], [4], [5], [6], [7], [8]