Radiation damage

Ionizing radiation damages tissues in different ways, depending on the type of radiation, its dose, degree, and type of external exposure. Symptoms may be local (eg, burns) or systemic (eg, acute radiation sickness). Diagnosis is based on the history of radiation exposure and sometimes on alpha counters or Geiger counters. Treatment of radiation injury consists of isolation and (if indicated) decontamination, but supportive care is generally indicated. In cases of internal contamination with specific radionuclides, absorption inhibitors or chelating agents are used. Prognosis is assessed by measuring the lymphocyte count during the first 24–72 hours.

Radiation is high-energy electromagnetic waves (X-rays, gamma rays) or particles (alpha particles, beta particles, neutrons) emitted by radioactive elements or artificial sources (such as X-ray tubes and radiation therapy equipment).

Alpha particles are helium nuclei emitted by various radionuclides (e.g. plutonium, radium, uranium), which 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 I). These particles can penetrate the skin to a greater depth (1-2 cm) and cause damage to the epithelium and subepithelial layer. Neutrons are electrically neutral particles emitted by nuclei of some radioactive atoms and formed as a result of nuclear reactions (e.g. in reactors, linear accelerators); they can penetrate deeply into tissues (more than 2 cm), where their collisions with stable atoms result in the emission of alpha and beta particles and gamma radiation. Gamma and X-ray radiation are high-energy electromagnetic radiation (i.e. photons) that can penetrate human tissue many centimeters deep.

Because of these characteristics, alpha and beta particles exert their primary damaging effect when the radioactive elements that emit them are inside the body (internal contamination) or directly on its surface. Gamma rays and X-rays can cause harm at a great distance from their source and are a typical cause of acute radiation syndromes (see the relevant section).

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

Radiation exposure. There are two main types of radiation exposure - contamination and irradiation. In many cases, radiation has both effects.

• Contamination is the entry and retention of radioactive material into the body, usually in dust or liquid. External contamination is on the skin or clothing, from which it may fall off or simply rub off, contaminating other people and surrounding objects. Radioactive material may also be absorbed through the lungs, gastrointestinal tract, or penetrated through the skin (internal contamination). Absorbed material is transported to various sites in the body (e.g., 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 radioactive substance (i.e. there is no contamination). As a rule, this effect is caused by gamma and X-ray radiation. Irradiation can cover the entire body with the formation of systemic symptoms and radiation syndromes (see the relevant section), or a small part of it (for example, during radiation therapy) with local manifestations.

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Pathophysiology of radiation injury

Ionizing radiation damages mRNA, DNA, and proteins directly or through the formation of highly reactive free radicals. High doses of ionizing radiation cause cell death, while lower doses impair cell proliferation. Damage to other cellular components results in progressive hypoplasia, atrophy, and ultimately fibrosis. Genetic damage can trigger malignant transformation or hereditary genetic defects.

Tissues that normally renew themselves rapidly and continuously are particularly vulnerable to ionizing radiation. Lymphoid cells are the most sensitive to radiation, followed in descending order by germ cells, dividing cells of the bone marrow, intestinal epithelial cells, epidermis, hepatocytes, epithelium of the alveoli of the lungs and bile ducts, renal epithelial cells, endothelial cells (pleura and peritoneum), nerve cells, bone cells, connective tissue cells, and muscle cells.

The exact dose at which toxicity begins depends on the dynamics of the irradiation, i.e. a single rapid dose of a few Gray is more destructive than the same dose given over weeks or months. The dose response also depends on the area of the body irradiated. The severity of the disease is undisputed, with fatal cases occurring with whole-body irradiation >4.5 Gy; however, doses of tens of Gray may be well tolerated if the irradiation is spread over a long period of time and focused on a small area of the body (e.g., cancer treatment).

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

Sources of radiation

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

Sources of radiation

Symptoms of radiation poisoning

The manifestations depend on whether the ionizing radiation affects the entire body (acute radiation syndrome) or only a part of the body.

Several different syndromes occur after whole body irradiation. 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);
• the acute phase of the disease (2-60 days after irradiation).

Symptoms of radiation poisoning

Diagnosis of radiation damage

Following acute irradiation, laboratory testing is performed, including CBC, blood chemistry, and urinalysis. Blood type, compatibility, and HLA antigens are determined in case of blood transfusions or, if necessary, stem cell transplantation. Lymphocyte counts are performed 24, 48, and 72 hours after irradiation to assess the initial radiation dose and prognosis. Clinical blood tests are repeated weekly. This is necessary to monitor bone marrow activity and, if necessary, depending on the clinical course.

Diagnosis of radiation damage

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Treatment of radiation damage

Ionizing exposure may be accompanied by physical injury (e.g. from an explosion or fall); the accompanying injury may be more life-threatening than the radiation exposure and requires immediate treatment. Treatment of serious injury should not be delayed until radiation diagnostic and protection services arrive. Standard precautions routinely used in trauma care are sufficient to protect rescuers.

Treatment of radiation damage

Prediction of radiation damage

Without medical care, the LD 50 (the dose that causes death in 50% of patients within 60 days) for whole-body irradiation is approximately 4 Gy; >6 Gy is almost always fatal. At doses <6 Gy, survival is possible inversely proportional to the total dose. The time to death is also inversely proportional to the dose (and hence the symptoms). Death occurs within hours to a few days for the cerebral syndrome and usually within 3-10 days for the gastrointestinal syndrome. For the hematologic syndrome, death is possible within 2-4 weeks due to secondary infection or within 3-6 weeks due to massive hemorrhage. Patients who have received whole-body irradiation doses <2 Gy usually recover completely within a month, although late complications (eg, cancer) are possible.

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

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