The dose of radiation that a person receives during medical procedures, according to various estimates, ranges from 20 to 30% of the total radiation background. 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 the water and the earth. “Medical” radiation - in second place in importance among all types of sources, significantly ahead of man-made radiation (from nuclear power plants, radioactive waste dumps, 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-ray radiation
According to scientists, one should not be afraid of the natural radiation background. 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. The exposure to which people are exposed as a result of x-ray studies, on average, is almost the same amount - about 1.2-1.5 mSv per year. Thus, the anthropogenic component doubles the dose received.
X-ray diagnostic technologies are widely used to detect many diseases. Despite the fact that in recent years in medicine there has been an intensive development of other technologies (computed tomography, MRI, ultrasound, thermal imaging), more than half of the diagnoses are established using x-rays.
By the beginning of the XXI century, almost all the technical capabilities for the maximum reduction of radiation exposure in X-ray diagnostics were also exhausted. The most effective method in this regard was the digital technique for converting x-ray images. The detector of a digital X-ray apparatus has a sensitivity several times higher than that of film ones, which made it possible to reduce the radiation dose.
Units
Unlike the natural background radiation, in medical research, irradiation is uneven. To determine the degree of harm that X-rays cause to humans, you first need to figure out in which units the radiation dose is measured.
To evaluate the effect of ionizing radiation in science, a special value was introduced - the equivalent dose of N. It takes into account the peculiarities of radiation exposure using weighting factors. Its value is defined as the product of the absorbed dose in the body by the weighting coefficient W R , which depends on the type of radiation (α, β, γ). The absorbed dose is calculated as the ratio of the amount of ionizing energy transferred to the substance to the mass of the substance in the same volume. It is measured in Grey (Gy).
The occurrence of negative consequences depends on the radiosensitivity of the tissues. For this, the concept of an effective dose was introduced, which is the sum of the products of H in the tissues by the weighting coefficient W t . Its significance depends on which organ was exposed. 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 Sievert (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, in practice, millisievert (mSv) and microsievert (ÎĽSv) are used.
Health hazard
The harmful effects of radiation on human health depend on the dose level and on the organ that has been exposed. When bone marrow is irradiated, blood diseases (leukemia and others) occur, when exposed to the genitals, genetic abnormalities in the offspring occur.
Large doses of radiation are considered 1 Gy or more. In this case, the following violations occur:
- damage to a significant number of tissue cells;
- the occurrence of radiation burns;
- radiation sickness;
- cataract and other pathologies.
At this dosage, physiological changes are inevitable. Irradiation can be obtained continuously for several hours or in total at intervals as a result of exceeding the general threshold level. The severity of the disease depends on the size of the dose received.
At medium (0.2-1 Gy) and small (<0.2 Gy) doses, spontaneous changes can occur, which appear after some time, after a latent (latent) period. It is assumed that such effects can also occur at low 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 this risk.
What types of examinations use x-rays?
Radiation exposure is used in the following types of examinations:
- fluorography, which is widely used for the diagnosis of tuberculosis as a preventive measure;
- traditional radiography;
- CT scan;
- angiography (blood vessel examination);
- radioimmune analysis.
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-type devices that are not equipped with a meter are used for examination, then the radiation output is determined using clinical dosimeters at a distance of 1 m from the focus of the radiating tube in operating modes.
Exposure registration
According to SanPiN 2.6.1.1192-03, the patient has the right to provide complete information about radiation exposure and its consequences, as well as to make an independent decision on conducting an X-ray examination.
The doctor of the X-ray room (or his laboratory assistant) must register the effective dose in the dose loading sheet. This sheet is pasted into the patient's outpatient card. Registration is also made in the register, which is kept in an X-ray room. However, in practice, these rules are often not respected. The reason for this lies in the fact that the x-ray dose is much lower than the critical.
Patient Ranking
Due to the presence of radiation exposure, x-ray studies are prescribed only for strict indications. All patients are divided into 3 groups:
- Blood pressure is those patients who are prescribed x-rays for malignant pathologies or suspected of them, as well as in cases where there are vital indications (for example, injuries). The maximum permissible dose per year is 150 mSv. Exposure to this value may cause radiation damage.
- DB - patients who are exposed to radiation in order to diagnose a disease of a non-malignant nature. For them, the dose should not exceed 15 mSv / year. When it is exceeded, the risk of developing diseases in the distant period and genetic mutations sharply increases.
- VD - a category of people who undergo a radiographic examination for preventive purposes, as well as those employees whose activities are associated with harmful conditions (the maximum permissible dose is 1.5 mSv).
Radiation doses
The following data gives an idea of ​​what kind of exposure with x-ray can be obtained during examinations:
- chest x-ray - 0.08 mSv;
- breast examination (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 in one procedure. Digital X-ray machines can reduce radiation exposure in the X-ray diagnostics to 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 higher this dose. In this regard, pilots have a sanitary norm for flight hours - not more than 80 per month.
How many times a year can I do x-rays?
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 approximately 10 radiographs and 20 digital fluoroscopy. If several different studies were performed (mammography, dental images), then the total annual dose can reach 15 mSv. In the USA, the standardized dose value is higher than in Russia - 3 mSv.
The occurrence of radiation 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 provide for only a single chest x-ray per year for preventive purposes.
These standards do not apply to those patients for whom X-ray irradiation is carried out for diagnostic purposes, in order to identify the disease for health reasons. In this case, the question of how many times a year you can do an x-ray is not regulated. The patient can take 4 pictures in 1 day, and several pictures every 1-2 weeks for 2-3 months.
MRI and CT
Magnetic resonance imaging - MRI - is often confused with x-ray examination. However, with this type of examination, no radiation load is created. 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 recorded and recorded in the form of images in a computer.
In contrast to MRI, a CT scan - CT scan - is characterized by the highest dose of radiation. In one session, you can get a radiation dose with an x-ray of the order of 4-5 mSv. This is almost ten times the dose from a conventional x-ray examination. Therefore, without special indications, CT is not recommended.
Is it possible to do x-rays for children?
Since children are more susceptible to x-rays, according to WHO recommendations, it is forbidden to do a preventive study in childhood (up to 17 years). Due to the smaller height and weight, the child receives a large specific radiation load.
However, for medical or diagnostic purposes, an X-ray is 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 to a child is decided by the attending physician. Moreover, preference should be given to those procedures for which the lowest dose of radiation is characteristic.
During CT, a 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 that such an examination be performed using “fast” tomography (the apparatus tube is rotated at a speed of 0.3 s per revolution).
When choosing a clinic where to take an X-ray of a child, one should give preference to those in which the most qualified and experienced staff so that in the future there is no need to repeat this procedure to clarify the diagnosis. According to recent studies, the risk of developing malignant diseases in children increases if the radiation dose is obtained with an x-ray of about 50 mSv. Therefore, do not refuse radiography if it is prescribed to a child for medical reasons.
Pregnant Examination
When radiographs of pregnant women are guided by the same principles as for children. According to the US Obstetrics College, the hazardous radiation level 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, a diagnosis of organs is required for health reasons, then you must agree to an x-ray. Stop breastfeeding after x-ray examination is also not worth it.
Computed tomography is performed only on strict indications when other research options have been exhausted. At the same time, they try to reduce the area of ​​influence and reduce the radiation dose using bismuth screens that do not affect the image quality.
Risk to doctors
Work in an x-ray room is associated with increased doses of radiation. However, studies show that, subject to all safety requirements, radiologists receive an annual dose of about 0.5 mSv. This is much lower than the normalized limit values. Only in special studies, when the doctor is forced to work in the immediate vicinity of the radiation beam, the total dose can approach the limit.
Once a year, X-ray personnel are required to undergo a medical examination with extensive tests. Persons who have a genetic predisposition to tumors and an unstable chromosome structure are not allowed to do this work.