Radiation damage

Ionizing radiation damages tissues in different ways, depending on the type of radiation, its dose, degree and type of external influence. Symptoms can be local (for example, burns) or systemic (in particular, acute radiation sickness). The diagnosis is determined by the history of exposure to radiation and sometimes using alpha-counters or Geiger counters. Treatment of radiation damage consists of isolation and (with indications) of decontamination, but supportive therapy is mainly shown. In the case of internal contamination with specific radionuclides, absorbing inhibitors or chelating agents are used. The prognosis is assessed by measuring the number of lymphocytes during the first 24-72 hours.

Radiation refers to high-energy electromagnetic waves (X-rays, gamma rays) or particles (alpha particles, beta particles, neutrons) emitted by radioactive elements or artificial sources (for example, an X-ray tube and equipment for radiotherapy).

Alpha particles are helium nuclei emitted by various radionuclides (for example, plutonium, radium, uranium) that do not penetrate the skin deeper than 0.1 mm. Beta particles are high-energy electrons emitted by nuclei of unstable atoms (in particular, ¹³⁷ Cs, ¹³¹ l). These particles can penetrate the skin to a great depth (1-2 cm) and cause damage to the epithelium and the subepithelial layer. Neutrons are electrically neutral particles emitted by the nuclei of some radioactive atoms and are formed as a result of nuclear reactions (for example, in reactors, linear accelerators); they can penetrate deeply into tissues (more than 2 cm), where as a result of their collision with stable atoms, alpha and beta particles and gamma radiation emit. Gamma and X-ray radiation is a high-energy electromagnetic radiation (ie, photons) that can penetrate human tissues deep into many centimeters.

In connection with these features, alpha and beta particles have a major damaging effect if the radioactive elements that emit them are inside the body (internal contamination) or directly on its surface. Gamma rays and X-rays can be harmful at a great distance from their source and serve as a typical cause of acute radiation syndromes (see the corresponding section).

Units. Distinguish the following units of measurement: X-ray, gray and sievert. X-ray (P) - the intensity of X-ray or gamma radiation in the air. Gray (Gr) is the amount of energy absorbed by the tissue. Since the biological damage for each Gray varies depending on the type of radiation (it is higher for neutrons and alpha particles), the dose in the Greens must be multiplied by the quality factor, which is another unit - sievert (Sv). Gray and Sievert replaced the units "rad" and "rem" (1 Gy = 100 rad, 1 Sv = 100 rem) in the modern nomenclature and are practically equivalent when describing gamma or beta radiation.

Impact of radiation. There are two main types of radiation exposure - pollution and exposure. In many cases, radiation has both effects.

• Pollution - the ingress and retention of radioactive material in the body, usually with dust or liquid. External contamination is on the skin or clothing with which it can fall or simply erase, contaminating other people and surrounding objects. Radioactive material can also be absorbed through the lungs, the gastrointestinal tract, or penetrate the skin (internal contamination). The absorbed substance is transported to various parts of the body (for example, bone marrow), where it continues to emit radiation until it is removed or until it decays. Internal contamination is more difficult to remove.
• Irradiation is the effect of penetrating radiation, but not of a radioactive substance (ie no contamination). As a rule, this action has gamma and X-ray radiation. Irradiation can cover the whole body with the formation of systemic symptoms and radiation syndromes (see the relevant section), or a small part of it (for example, with radiation therapy) with local manifestations.

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

Pathophysiology of radiation injury

Ionizing radiation damages mRNA, DNA and proteins directly or through the formation of highly active free radicals. Large doses of ionizing radiation cause cell death, while lower doses disrupt their proliferation. Damage to other cellular components leads to progressive hypoplasia, atrophy and, ultimately, fibrosis. Genetic damage can provoke malignant transformation or genetic defects inherited.

Fabrics, normally quickly and continuously updated, are particularly vulnerable to ionizing radiation. The most sensitive to radiation are lymphoid cells, followed by (in descending order) sex cells, dividing bone marrow cells, intestinal epithelial cells, epidermis, hepatocytes, epithelium of the lung and bile duct alveoli, renal epithelial cells, endothelial cells (pleura and peritoneum) cells, bone cells, cells of connective tissue and muscles.

The exact dose at which the toxic effect begins depends on the dynamics of irradiation, i.e. A single rapid dose of several Grays is more destructive than the same dose that is effective for weeks or months. The reaction to the dose also depends on the area of the irradiated part of the body. The severity of the disease is undeniable, fatal cases occur when the whole body is irradiated at a dose> 4.5 Gy; nevertheless, dozens of gray doses can be tolerated well if the irradiation occurs for a long period of time and is focused on a small part of the body (for example, in the treatment of cancer).

Children are more susceptible to radiation damage due to the greater proliferation rate of their cells and a greater number of cell divisions.

Sources of radiation

People are constantly exposed to natural radiation (radiation background). The radiation background includes cosmic radiation, most of which is absorbed by the atmosphere. Thus, the background acts more on people living in the highlands, or flying in an airplane. Radioactive elements, especially radon gas, are found in many rocks or minerals. These elements fall into various substances, including food and building materials. Radon exposure is usually 2/3 of the total dose of natural radiation.

Sources of radiation

Symptoms of radiation injury

Manifestations depend on whether ionizing radiation is acting on the whole organism (acute radiation syndrome) or only on the site of the body.

There are several different syndromes after irradiation of the whole organism. These syndromes have three phases:

• prodromal phase (from 0 to 2 days after irradiation) with general weakness, nausea and vomiting;
• latent asymptomatic phase (1 -20 days after irradiation);
• phase of the height of the disease (2-60 days after irradiation).

Symptoms of radiation injury

Diagnostics of radiation damage

After acute irradiation, a laboratory examination, including OAK, a biochemical blood test, a general urine test, is performed. Determine the blood group, compatibility and HLA antigens in case of blood transfusion or, if necessary, stem cell transplantation. Lymphocyte counts are performed 24, 48 and 72 hours after irradiation to assess the initial dose of radiation and the prognosis. A clinical blood test is repeated weekly. This is necessary to control the activity of the bone marrow and, if necessary, depending on the clinical course.

Diagnostics of radiation damage

[7], [8], [9], [10], [11], [12],

Treatment of radiation injury

Ionizing effects can be accompanied by physical damage (for example, from an explosion or a fall); Concomitant injury can be more life threatening than radiation exposure and requires priority treatment. Assistance in case of serious injury should not be postponed until the arrival of radiation diagnostics and protection services. The standard precautions routinely used to help the injured are sufficient to protect rescuers.

Treatment of radiation injury

Forecast of radiation damage

Without medical assistance, LD 50 (the dose that causes the death of 50% of patients for 60 days) with whole body irradiation is approximately 4 Gy; > 6 Gy is almost always deadly. At a dose of <6 Gy, survival is possible in the proportion of the reciprocal of the total dose. The term of death is also inversely proportional to the dose (and therefore, symptomatology). Death occurs within hours or a few days with cerebral syndrome and usually within 3-10 days with gastrointestinal syndrome. With hematological syndrome, death is possible in the period of 2-4 weeks because of secondary infection or within 3-6 weeks because of massive bleeding. Patients who received whole body irradiation at a dose of <2 Gy usually recover completely within a month, although they may have long-term complications (eg, cancer).

In the treatment of LD 50 is about 6 Gy, in some cases, patients survived after irradiation of 10 Gy.

[13], [14], [15]