The effects of long-term x-rays on the human body

The impact and harm of Pathological reactions caused by the body.

Acute radiation injury is caused by a large dose of radiation in one time or in a short period of time, and mainly occurs in accidental exposure. In the case of chronic low-dose continuous irradiation, what deserves attention is chronic radiation damage, which is mainly caused by X-ray professionals not paying attention to protection on weekdays and receiving excessive doses for a long time.

Ionizing radiation can not only cause systemic acute and chronic radiation damage, but also cause local skin damage. In the second year after the discovery of X-rays, Grube, the manufacturer of X-ray tubes, developed atopic dermatitis on his hands. In 1899, Stevens first reported the damage of X-rays to the skin.

Human experience has proven that the application of X-rays can bring huge benefits to mankind (such as radiological diagnosis, radiotherapy, etc.), but if no attention is paid to protection or improper use during application. It can also cause certain harm (such as injury to individuals or an increase in the incidence of cancer among the population). Therefore, this chapter starts from the needs of radiation protection and introduces the basic knowledge about radiation damage in order to deeply understand the basis for formulating radiation protection standards and the necessity of good protection.

1. Radiation Damage Mechanism

When X-rays irradiate living organisms, they interact with body cells, tissues, body fluids and other substances, causing ionization of atoms or molecules of the substances, so they can directly destroy Certain macromolecular structures in the body, such as breaking protein molecular chains, breaking ribonucleic acid or deoxyribonucleic acid, destroying some enzymes that are important for substance metabolism, etc., can even directly damage cell structures. In addition, rays can ionize water molecules widely present in the body to form some free radicals, which can damage the body through the indirect action of these free radicals. The pathogenesis of radiation injury is the same as that of other diseases. After the pathogenic factors act on the body, in addition to causing changes at the molecular and cellular levels, they can also produce a series of secondary effects, ultimately leading to organ-level disorders and even overall-level changes. , signs and symptoms of radiation injury may appear clinically. Damage to human cells is limited to the individual itself, causing physical effects. Damage to germ cells will affect the offspring of the exposed individual and produce genetic effects. Stochastic effects can occur when a single or a small number of cells are damaged by radiation (mainly chromosomal aberrations, gene mutations, etc.). Radiation can cause non-stochastic effects by destroying large numbers of cells. In the development process of radiation injury, the body's response further plays a major role, first of all, it depends on the function of the nervous system, especially high-level neural activity, and secondly, it depends on the regulation of body fluids. It can be seen from this that the diseases of higher animals cannot only be attributed to the processes produced in those simple or isolated cells, but contain very complex processes.

2. Factors affecting radiation damage

The biological effects caused by radiation acting on the body are related to many factors. Such as the nature and intensity of radiation; personal characteristics, such as sensitivity, age, gender, past medical history and health status, working environment, etc.

(1) Radiation properties

Radiation properties include the type and energy of rays. Different types of rays have different linear energy transfer densities (LET) in the medium and produce different ionization densities, so their relative biological effects are different. The biological effects of X-rays and rays are basically the same. The LET of neutrons is much larger. The biological effect produced by fast neutrons of 1-10 MeV is 10 times greater than that of X-rays and R-rays.

The same type of rays will produce different biological effects due to different ray energies. For example, low-energy X-rays require less exposure than high-energy X-rays to cause skin erythema. This is because low-energy X-rays are mainly absorbed by the skin, while when high-energy X-rays are irradiated, the energy can reach deep tissues, which is not only valuable for radiotherapy, but also very meaningful in radiation protection.

(2) X-ray dose

After rays act on the body, the damage to the body caused is directly related to the X-ray dose. When animals are irradiated with different doses, it can be found that signs of acute radiation sickness begin to appear when the dose reaches a certain amount. When the dose continues to be increased, death may occur. The greater the dose, the higher the mortality rate. When the dose is increased to a certain large, then Mortality occurred in 100% of animals.

(3) Dose rate

Dose rate is the absorbed dose per unit time. Generally speaking, when the total dose is the same, the higher the dose rate, the greater the biological effect. However, when the dose rate reaches a certain value, the proportional relationship between the biological effect and the dose rate is lost. Under extremely low dose rate conditions, when damage to the body is balanced by its repair, the body can be exposed to long-term irradiation without damage. Long-term exposure to small doses can cause chronic radiation damage when the cumulative dose is large.

(4) Irradiation mode

The total dose is the same, but the effects produced by single-directional irradiation and multi-directional irradiation are different. The effects produced are also different between single exposure and multiple exposures, as well as the time intervals between multiple exposures.

(5) Irradiation site and range

Each part of the body has different radiation sensitivity to rays. The so-called radiation sensitivity refers to the body’s resistance to ionizing radiation, that is, the response to radiation. Depending on the intensity or time, tissues with high radiation sensitivity are easily damaged.

The general rule of cells to radiation is that cells in a normal dividing state are sensitive to radiation, while cells that are not dividing normally are resistant to radiation.

The sensitivity of various human tissues to radiation is roughly in the following order:

1. Highly sensitive tissue

Lymphoid tissue (lymphocytes and immature lymphocytes);

Thymus (thymocytes); bone marrow tissue ( immature red, granulocytes and megakaryocytes);

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Gastrointestinal epithelium, especially small intestinal crypt epithelial cells;

Gonads (spermatogonia, egg cells);

Embryonic tissue.

2. Moderately sensitive tissues

Sensory organs (cornea, lens, conjunctiva);

Endothelial cells (mainly blood vessels, sinusoids and lymphatic endothelial cells);

Skin epithelium (including hair follicle epithelial cells);

Salivary glands;

Epithelial cells of kidney, liver, and lung tissues.

3． Mildly sensitive tissues

Central nervous system;

Endocrine (except gonads);

Heart.

4． Insensitive tissues

Muscle tissue;

Cartilage and bone tissue;

Connective tissue.

At the same dose, the biological effects increase with the expansion of the irradiation range. Whole-body irradiation is more harmful than local irradiation.

(6) Environmental factors

Under low temperature and hypoxia conditions, radiation effects can be delayed and reduced. In addition, the effects will be different depending on the age, gender, health condition, mental state and nutritional status of the person being exposed. It can be seen that the body's response to radiation is affected by various factors.