The dose of radiation that a person receives during medical procedures, according to various estimates, ranges from 20 to 30% of the total background radiation. Radioactive radiation is always present in the environment - people receive it from the sun, from the bowels of the earth, from radionuclides that are in water and earth. "Medical" radiation is in second place in terms of importance among all types of sources, significantly ahead of man-made radiation (from nuclear power plants, radioactive waste disposal sites, household appliances, cell phones). Let's try to figure out how the radiation dose is calculated for x-rays and how dangerous it is.
X-rays
According to scientists, you should not be afraid of the natural background radiation. Moreover, it helps the development and growth of all living organisms on Earth. Every year a person receives a uniform dose of radiation equal to 0.7-1.5 mSv. Exposure to which people are exposed as a result of X-ray examinations, on average, is almost the same value - about 1.2-1.5 mSv per year. Thus, the anthropogenic componentdoubles the dose received.
X-ray diagnostic technologies are widely used to detect many diseases. Despite the fact that in recent years there has been an intensive development of other technologies in medicine (computed tomography, MRI, ultrasound, thermal imaging), more than half of the diagnoses are made using X-rays.
By the beginning of the 21st century, almost all technical possibilities for the maximum reduction of radiation exposure in X-ray diagnostics were also exhausted. The most effective method in this regard has become a digital technique for converting x-ray images. The detector of a digital X-ray machine has a sensitivity that is several times higher than that of film ones, which makes it possible to reduce the radiation dose.
Units of measure
Unlike natural background radiation, radiation exposure in medical research is uneven. To determine the degree of harm that X-rays cause to a person, you first need to figure out in what units the radiation dose is measured.
To assess the effect of ionizing radiation in science, a special value was introduced - the equivalent dose H. It takes into account the characteristics of radiation exposure using weighting factors. Its value is defined as the product of the absorbed dose in the body by the weighting coefficient WR, which depends on the type of radiation (α, β, γ). The absorbed dose is calculated as the ratio of the amountionizing energy transferred to the substance, to the mass of the substance in the same volume. It is measured in Grays (Gy).
The occurrence of negative effects depends on the radiosensitivity of tissues. For this, the concept of effective dose was introduced, which is the sum of the products of H in tissues and the weighting coefficient Wt. Its value depends on which organ was affected. So, with an x-ray of the esophagus, it is 0.05, and with irradiation of the lungs - 0.12. The effective dose is measured in Sieverts (Sv). 1 Sievert corresponds to such an absorbed dose of radiation for which the weighting factor is 1. This is a very large value, therefore millisieverts (mSv) and microsieverts (µSv) are used in practice.
He alth damage
The harmful effects of radiation on human he alth depend on the dose level and on the organ that was exposed. Irradiation of the bone marrow causes blood diseases (leukemia and others), and exposure to the genital organs causes genetic abnormalities in the offspring.
Large doses of radiation are 1 Gy or more. In this case, the following violations occur:
- damage to a significant number of tissue cells;
- radiation burns;
- radiation sickness;
- cataracts and other pathologies.
At this dosage, physiological changes are inevitable. Exposure can be received continuously for several hours or cumulatively at intervals as a result of exceeding the overall threshold level. The severity of the disease depends on the amount ofdoses.
With medium (0.2-1 Gy) and low (<0.2 Gy) doses, spontaneous changes may occur, which appear after a while, after a latent (latent) period. It is assumed that such effects can also occur at low radiation doses. The severity of the disease in this case does not depend on the dose received. Violations most often occur in the form of cancerous tumors and genetic abnormalities. Malignant neoplasms can appear after several decades. However, studies show that no more than 1% of patients are at risk.
What types of examinations are X-rays used for?
Radiation exposure is used in the following types of examinations:
- fluorography, which is widely used to diagnose tuberculosis for preventive purposes;
- conventional radiography;
- computed tomography;
- angiography (examination of blood vessels);
- radioimmunoassay.
How is radiation exposure determined?
All modern x-ray machines are equipped with a special meter that automatically determines the effective dose of radiation, taking into account the area of exposure. Built-in dosimeters are used as detectors.
If old-style devices that are not equipped with a meter are used for the examination, then the radiation output is determined using clinical dosimeters at a distance of 1 m from the focusradiant tube in operating modes.
Irradiation registration
According to SanPiN 2.6.1.1192-03, the patient has the right to provide full information about radiation exposure and its consequences, as well as to independently decide on an X-ray examination.
The X-ray doctor (or his laboratory assistant) must record the effective dose on the dose record sheet. This sheet is pasted into the patient's outpatient record. Registration is also made in the register, which is kept in the X-ray room. However, these rules are often not respected in practice. The reason for this lies in the fact that the radiation dose for X-rays is much lower than the critical one.
Ranking patients
Due to the presence of radiation exposure, X-ray examinations are prescribed only for strict indications. All patients are divided into 3 groups:
- BP - these are those patients who are prescribed X-rays for malignant pathologies or suspicion of them, as well as in cases where there are vital indications (for example, injuries). The maximum allowable dose per year is 150 mSv. Exposure above this value may cause radiation injury.
- BD - patients who are irradiated for the purpose of diagnosing any disease of a non-malignant nature. For them, the dose should not exceed 15 mSv/year. If it is exceeded, the risk of diseases in the long-term period and genetic mutations increases sharply.
- VD is a category of persons whox-ray examination is carried out for preventive purposes, as well as those workers whose activities are associated with harmful conditions (the maximum allowable dose is 1.5 mSv).
Irradiation doses
The following data gives an idea of what X-ray exposure can be obtained during examinations:
- chest fluorography – 0.08 mSv;
- breast examinations (mammography) – 0.8 mSv;
- x-ray of the esophagus and stomach – 0.046 mSv;
- X-ray of teeth – 0.15-0.35 mSv.
On average, a person receives a dose of 0.11 mSv per procedure. Digital X-ray machines can reduce the radiation exposure in X-ray diagnostics to a value of 0.04 mSv. For comparison, when flying for 8 hours in an airplane, it is 0.05 mSv, and the higher the flight altitude on long-haul routes, the greater this dose. In this regard, pilots have a sanitary standard for flight hours - no more than 80 per month.
How many times a year can I take an X-ray?
In medicine, there is a maximum total dose of radiation received - 1 mSv per year. However, it should be noted that this value is indicated for preventive studies. This corresponds to about 10 radiographs and 20 digital fluorography. If several different studies were carried out (mammography, dental imaging), then the total annual dose can reach 15 mSv. In the USA, the normalized dose value is higher than in Russia - 3 mSv.
KRadiation sickness is caused by a dose ten times greater - about 1 Sv. Moreover, this should be radiation received by a person in 1 session. Despite this difference, the regulations only require a chest X-ray once a year for preventive purposes.
These standards do not apply to those patients for whom X-ray exposure is performed for diagnostic purposes, to detect a disease for he alth reasons. In this case, the question of how many times a year X-rays can be done is not regulated. The patient can take 4 shots in 1 day, and several shots every 1-2 weeks for 2-3 months.
MRI and CT
Magnetic resonance imaging - MRI - is often confused with x-rays. However, this type of examination does not create any radiation load. The principle of this technology is based on the magnetic properties of tissues. The hydrogen protons contained in them release energy under the influence of radio frequency pulses. This energy is registered and processed in the form of pictures in the computer.
In contrast to MRI, computed tomography - CT - is characterized by the highest dose of radiation. In one session, you can get a radiation dose with X-rays of the order of 4-5 mSv. This is almost tens of times higher than the dose from a conventional X-ray examination. Therefore, without special indications, CT is not recommended.
Can children take x-rays?
Because children are more susceptible toX-rays, then, according to WHO recommendations, it is forbidden to do a preventive examination in childhood (up to 17 years). Due to smaller height and weight, the child receives a greater specific radiation load.
However, for medical or diagnostic purposes, X-rays are still carried out for children. This applies to those cases when the child is injured (fractures, dislocations), with pathologies of the brain, gastrointestinal tract, with suspected pneumonia, ingestion of foreign objects and other disorders. The question of whether it is possible to take an x-ray for a child is decided by the attending physician. In this case, preference should be given to those procedures that are characterized by the lowest dose of radiation.
When conducting CT, the reduction in exposure for a child is achieved by reducing the duration of exposure, increasing the distance to the emitter and shielding. It is recommended to conduct such an examination using "fast" tomography (rotation of the tube of the apparatus is performed at a speed of 0.3 s per 1 revolution).
When choosing a clinic where to take an x-ray for a child, you need to give preference to those in which the most qualified and experienced staff, so that in the future you do not have to repeat this procedure to clarify the diagnosis. According to recent studies, the risk of developing malignant diseases in children increases if an X-ray dose of about 50 mSv is received. Therefore, you should not refuse radiography if it is prescribed for a child for medical reasons.
Examination of pregnant women
X-rays of pregnant women are guided by the same principles as for children. According to the US College of Obstetricians, a dangerous level of radiation for the fetus is 50 mGy. X-rays are usually taken in the second trimester of pregnancy. If a serious injury is received or there is a suspicion of it, diagnostics of organs is required for he alth reasons, then an x-ray must be agreed. Stopping breastfeeding after an X-ray examination is also not worth it.
Computed tomography is performed only for strict indications, when other research options have been exhausted. At the same time, they try to reduce the exposure area and reduce the radiation dose using bismuth screens that do not affect the quality of the image.
Risk for doctors
Work in the x-ray room is associated with increased doses of radiation. However, studies show that if all safety requirements are met, radiologists receive an annual dose of about 0.5 mSv. This is well below the normalized limit values. Only in special studies, when the doctor is forced to work in close proximity to the radiation beam, the total dose can approach the limit value.
Once a year, the staff of X-ray rooms are supposed to undergo a medical examination with detailed analyzes. Persons who have a genetic predisposition to tumors and an unstable chromosome structure are not allowed to such work.
