All chemical elements form isotopes with unstable nuclei, which emit α-particles, β-particles or γ-rays during their half-life. Iodine has 37 types of nuclei with the same charge, but differing in the number of neutrons that determine the mass of the nucleus and the atom. The charge of all isotopes of iodine (I) is 53. When they mean an isotope with a certain number of neutrons, write this number next to the symbol, through a dash. In medical practice, I-124, I-131, I-123 are used. The normal isotope of iodine (not radioactive) is I-127.

The number of neutrons serves as an indicator for various diagnostic and therapeutic procedures. Radioiodine therapy is based on the varying half-lives of the radioactive isotopes of iodine. For example, an element with 123 neutrons decays in 13 hours, with 124 - in 4 days, and I-131 will have a radioactive effect after 8 days. More often, I-131 is used, during the decay of which γ-rays, inert xenon and β-particles are formed.

The effect of radioactive iodine in the treatment

Iodine therapy is prescribed after the removal of the thyroid gland completely. With partial removal or conservative treatment, this method does not make sense to use. The follicles of the thyroid gland receive iodides from the tissue fluid that surrounds them. Iodides enter the tissue fluid by diffusion or by active transport from the blood. During iodine starvation, secretory cells begin to actively capture radioactive iodine, and degenerate cancer cells do this much more intensively.

β-particles, released during half-life, kill cancer cells.

The striking ability of β-particles acts at a distance of 600 - 2000 nm, which is quite enough to destroy only the cellular elements of malignant cells, and not neighboring tissues.

The main goal of radioiodine therapy is the final removal of all remnants of the thyroid gland, because even the most skillful operation leaves behind these remnants. Moreover, in the practice of surgeons, it has already become customary to leave several gland cells around the parathyroid glands for their normal operation, as well as around the recurrent nerve that innervates the vocal cords. The destruction of the iodine isotope occurs not only in the residual tissues of the thyroid gland, but also metastasis in cancerous tumors, which makes it easier to monitor the concentration of thyroglobulin.

γ-rays do not have a therapeutic effect, but they are successfully used in the diagnosis of diseases. The γ-camera built into the scanner helps to determine the localization of radioactive iodine, which serves as a signal for the recognition of cancerous metastases. The accumulation of the isotope occurs on the surface of the front of the neck (in the place of the former thyroid gland), in the salivary glands, along the entire length of the digestive system, in the bladder. Few, but still there are iodine uptake receptors in the mammary glands. Scanning reveals metastases in trimmed and nearby organs. Most often they are found in the cervical lymph nodes, bones, lungs and tissues of the mediastinum.

Treatment prescriptions for radioactive isotopes

Radioiodine therapy is indicated for use in two cases:

1. If the state of a hypertrophied gland is detected in the form of a toxic goiter (nodular or diffuse). The state of diffuse goiter is characterized by the production of thyroid hormones by the entire secretory tissue of the gland. In nodular goiter, only the nodular tissue secretes hormones. The tasks of introducing radioactive iodine are reduced to the inhibition of the functionality of hypertrophied areas, since the radiation of β-particles destroys precisely those places that are prone to thyrotoxicosis. At the end of the procedure, either the normal function of the gland is restored, or hypothyroidism develops, which is easily normalized when using an analogue of the hormone thyroxine - T4 (L-form).
2. If a malignant neoplasm of the thyroid gland (papillary or follicular cancer) is found, the surgeon determines the degree of risk. In accordance with this, risk groups are distinguished according to the level of tumor progress and possible distant localization of metastases, as well as the need for radioactive iodine treatment.
3. The low-risk group includes patients with a small tumor, not exceeding 2 cm and located in the outline of the thyroid gland. No metastases were found in neighboring organs and tissues (especially in the lymph nodes). Such patients do not need to inject radioactive iodine.
4. Patients with an average risk have a tumor larger than 2 cm, but not exceeding 3 cm. If an unfavorable prognosis develops and the capsule in the thyroid gland germinates, a dose of radioactive iodine of 30-100 mCi is prescribed.
5. The high-risk group has a pronounced aggressive pattern of cancer growth. There is germination in neighboring tissues and organs, lymph nodes, there may be distant metastases. Such patients require treatment with a radioactive isotope greater than 100 millicuries.

Radioiodine Administration Procedure

The radioactive isotope of iodine (I-131) is synthesized artificially. It is taken in the form of gelatin capsules (liquid) orally. Capsules or liquid are odorless and tasteless, swallowed only with a glass of water. After taking the liquid, it is recommended to immediately rinse your mouth with water and swallow it without spitting it out.

In the presence of dentures, it is better to remove them for a while before using liquid iodine.

You can’t eat for two hours, you can (even need) to take a plentiful drink of water or juice. Iodine-131, not absorbed by the thyroid follicles, is excreted in the urine, so urination should occur every hour with the control of the content of the isotope in the urine. Medicines for the thyroid gland are taken no earlier than 2 days later. It is better if the patient's contacts with other people at this time are strictly limited.

Before the procedure, the doctor must analyze the medications taken and stop them at different times: some of them - a week, others at least 4 days before the procedure. If a woman is of childbearing age, then pregnancy planning will have to be postponed for a period determined by the doctor. Previous surgery requires a test for the presence or absence of tissue capable of absorbing iodine-131. 14 days before the start of the introduction of radioactive iodine, a special diet is prescribed, in which the normal isotope of iodine-127 must be completely eliminated from the body. The list of products for the effective removal of iodine will be prompted by the attending physician.

Treatment of cancerous tumors with radioactive iodine

If the iodine-free diet is correctly observed and the period of restrictions on the intake of hormonal drugs is observed, the thyroid cells are completely cleared of iodine residues. With the introduction of radioactive iodine against the background of iodine starvation, cells tend to capture any isotope of iodine and are affected by β-particles. The more actively cells absorb a radioactive isotope, the more they are affected by it. The dose of irradiation of thyroid follicles that capture iodine is several tens of times greater than the effect of a radioactive element on surrounding tissues and organs.

French experts have calculated that almost 90% of patients with lung metastases survived after treatment with a radioactive isotope. Survival within ten years after the application of the procedure was more than 90%. And these are patients with the last (IVc) stage of a terrible disease.

Of course, the described procedure is not a panacea, because complications after its use are not excluded.

First of all, it is sialadenitis (inflammation of the salivary glands), accompanied by swelling, soreness. This disease develops in response to the introduction of iodine and the absence of thyroid cells capable of capturing it. Then the salivary gland has to take over this function. It should be noted that sialadenitis progresses only at high radiation doses (above 80 mCi).

There are cases of violation of the reproductive function of the reproductive system, but with repeated exposures, the total dose of which exceeds 500 mCi.

Treatment after thyroidectomy

Often, cancer patients are prescribed iodine therapy after removal of the thyroid gland. The objective of this procedure is the final defeat of cancer cells remaining after the operation, not only in the thyroid gland, but also in the blood.

After taking the drug, the patient is placed in a single room, which is equipped in accordance with the specifics.

Medical personnel are limited to contact for up to five days. At this time, visitors should not be allowed into the ward, especially pregnant women and children, in order to protect them from the flow of radiation particles. Urine and saliva of the patient are considered radioactive and are subject to special disposal.

Pros and cons of radioactive iodine treatment

The described procedure cannot be called completely “harmless”. Thus, during the action of a radioactive isotope, temporary phenomena are noted in the form of painful sensations in the region of the salivary glands, tongue, and front of the neck. The mouth is dry, itchy in the throat. The patient is sick, there is frequent urge to vomit, swelling, food becomes not tasty. In addition, old chronic diseases become aggravated, the patient becomes lethargic, gets tired quickly, and is prone to depression.

Despite the negative aspects of treatment, the use of radioactive iodine is increasingly used in the treatment of thyroid gland in clinics.

The positive reasons for this pattern are:

• there is no surgical intervention with cosmetic consequences;
• general anesthesia is not required;
• the relative cheapness of European clinics compared to operations with a high quality of service and scanning equipment.

Danger of radiation on contact

It should be remembered that the benefit provided in the process of using radiation is obvious to the patient himself. For the people around him, radiation can play a cruel joke. Not to mention the visitors of the patient, let us mention that medical workers provide care only when necessary and, of course, in protective clothing and gloves.

After discharge, you should not be in contact with a person closer than 1 meter, and with a long conversation, you should move 2 meters away. In the same bed, even after discharge, it is not recommended to sleep in the same bed with another person for 3 days. Sexual contacts and being near a pregnant woman are strictly prohibited within a week from the date of discharge, which occurs five days after the procedure.

How to behave after irradiation with an isotope of iodine?

Eight days after discharge, children should be kept away from themselves, especially contact. After using the bathroom or toilet, flush three times with water. Hands are washed thoroughly with soap.

It is better for men to sit on the toilet when urinating to prevent splashing of radiation urine. Breastfeeding should be discontinued if the patient is a nursing mother. The clothes in which the patient was on treatment are placed in a bag and washed separately a month or two after discharge. Personal belongings are removed from common areas and storage. In case of emergency admission to the hospital, it is necessary to warn the medical staff about the recent course of iodine-131 irradiation.

Scheme of the decay of iodine-131 (simplified)

Iodine-131 (iodine-131, 131 I), also called radioiodine(despite the presence of other radioactive isotopes of this element), is a radioactive nuclide of the chemical element iodine with atomic number 53 and mass number 131. Its half-life is about 8 days. The main application is found in medicine and pharmaceuticals. It is also one of the main products of fission of uranium and plutonium nuclei, which pose a risk to human health, which made a significant contribution to the harmful effects on human health after the nuclear tests of the 1950s, the Chernobyl accident. Iodine-131 is a significant fission product of uranium, plutonium and, indirectly, thorium, accounting for up to 3% of nuclear fission products.

Standards for the content of iodine-131

Treatment and prevention

Application in medical practice

Iodine-131, as well as some radioactive isotopes of iodine (125 I, 132 I), are used in medicine for the diagnosis and treatment of thyroid diseases. According to the radiation safety standards NRB-99/2009 adopted in Russia, discharge from the clinic of a patient treated with iodine-131 is allowed when the total activity of this nuclide in the patient's body decreases to a level of 0.4 GBq.

see also

Notes

Links

• Patient brochure on radioactive iodine treatment From the American Thyroid Association

Radioiodine, or rather one of the radioactive (beta and gamma radiation) isotopes of iodine with a mass number of 131 with a half-life of 8.02 days. Iodine-131 is known primarily as a fission product (up to 3%) of uranium and plutonium nuclei, released during accidents at nuclear power plants.

Obtaining radioiodine. Where does it come from

The isotope iodine-131 does not occur in nature. Its appearance is associated only with the work of pharmacological production, as well as nuclear reactors. It is also released during nuclear tests or radioactive disasters. So it increased the content of the iodine isotope in sea and tap water in Japan, as well as in food. The use of special filters helped to reduce the spread of isotopes, as well as to prevent possible provocations at the facilities of the destroyed nuclear power plant. Similar filters are produced in Russia at the NTC Faraday company.

Irradiation of thermal neutron targets in a nuclear reactor makes it possible to obtain iodine-131 with a high content.

Characteristics of iodine-131. Harm

The half-life of radioiodine of 8.02 days, on the one hand, does not make iodine-131 highly active, and on the other hand, allows it to spread over large areas. This is also facilitated by the high volatility of the isotope. So - about 20% of iodine-131 were thrown out of the reactor. For comparison, cesium-137 is about 10%, strontium-90 is 2%.

Iodine-131 forms almost no insoluble compounds, which also helps distribution.

Iodine itself is a deficient element and the organisms of people and animals have learned to concentrate it in the body, the same applies to radioiodine, which is not good for health.

If we talk about the dangers of iodine-131 for humans, then we are talking primarily about the thyroid gland. The thyroid gland does not distinguish ordinary iodine from radioiodine. And with its mass of 12-25 grams, even a small dose of radioactive iodine leads to irradiation of the organ.

Iodine-131 causes mutations and cell death, with an activity of 4.6 10 15 Bq / gram.

Iodine-131. Benefit. Application. Treatment

In medicine, the isotopes iodine-131, as well as iodine-125 and iodine-132, are used to diagnose and even treat thyroid problems, in particular Graves' disease.

During the decay of iodine-131, a beta particle appears with a high flight speed. It is able to penetrate into biological tissues at a distance of up to 2 mm, which causes cell death. In the case of the death of infected cells, this causes a therapeutic effect.

Iodine-131 is also used as an indicator of metabolic processes in the human body.

Release of radioactive iodine 131 in Europe

On February 21, 2017, information appeared in the news reports that European stations in more than a dozen countries from Norway to Spain had noticed an excess of the norms for the content of iodine-131 in the atmosphere for several weeks. Assumptions have been made about the sources of the isotope - a release on

How Radioactive Iodine Is Obtained 131. Radioactive Iodine and Thyroid Cancer During fission, various isotopes are formed, one might say, half of the periodic table. The probability of producing isotopes is different. Some isotopes are more likely to be formed, some are much less (see figure). Almost all of them are radioactive. However, most of them have very short half-lives (minutes or less) and rapidly decay into stable isotopes. However, among them there are isotopes that, on the one hand, are readily formed during fission, and on the other hand, have half-lives of days and even years. They are the main danger for us. Activity, i.e. the number of decays per unit time and, accordingly, the number of "radioactive particles", alpha and/or beta and/or gamma, is inversely proportional to the half-life. Thus, if there are the same number of isotopes, the activity of an isotope with a shorter half-life will be higher than with a longer one. But the activity of an isotope with a shorter half-life will fall off faster than one with a longer one. Iodine-131 is formed during fission with approximately the same "hunt" as cesium-137. But iodine-131 has a half-life of "only" 8 days, while cesium-137 has about 30 years. In the process of fission of uranium, at first the number of its fission products, both iodine and cesium, increases, but soon equilibrium comes to iodine - how much it is formed, so much decays. With caesium-137, due to its relatively long half-life, this equilibrium is far from being reached. Now, if there was a release of decay products into the external environment, at the initial moments of these two isotopes, iodine-131 poses the greatest danger. Firstly, due to the peculiarities of fission, a lot of it is formed (see Fig.), and secondly, due to the relatively short half-life, its activity is high. Over time (after 40 days), its activity will drop by 32 times, and soon it will practically not be visible. But cesium-137 at first may not "shine" so much, but its activity will subside much more slowly. Below are the most "popular" isotopes that pose a danger in case of accidents at nuclear power plants. radioactive iodine Among the 20 radioisotopes of iodine formed in the fission reactions of uranium and plutonium, a special place is occupied by 131-135 I (T 1/2 = 8.04 days; 2.3 h; 20.8 h; 52.6 min; 6.61 h), characterized by a high yield in fission reactions, high migratory ability and bioavailability. In the normal mode of operation of nuclear power plants, releases of radionuclides, including radioisotopes of iodine, are small. Under emergency conditions, as evidenced by major accidents, radioactive iodine, as a source of external and internal exposure, was the main damaging factor in the initial period of the accident. Simplified scheme for the decay of iodine-131. The decay of iodine-131 produces electrons with energies up to 606 keV and gamma quanta, mainly with energies of 634 and 364 keV. The main source of radioiodine intake for the population in the zones of radionuclide contamination was local food of plant and animal origin. A person can receive radioiodine along the chains: plants → human, plants → animals → human, water → hydrobionts → human. Surface contaminated milk, fresh dairy products and leafy vegetables are usually the main source of radioiodine intake for the population. Assimilation of the nuclide by plants from the soil, given the short period of its life, is of no practical importance. In goats and sheep, the content of radioiodine in milk is several times higher than in cows. Hundredths of incoming radioiodine accumulate in animal meat. Significant amounts of radioiodine accumulate in the eggs of birds. The coefficients of accumulation (excess over the content in water) 131 I in marine fish, algae, mollusks reaches 10, 200-500, 10-70, respectively. The isotopes 131-135 I are of practical interest. Their toxicity is low compared to other radioisotopes, especially alpha-emitting ones. Acute radiation injuries of severe, moderate and mild degree in an adult can be expected with oral intake of 131 I in the amount of 55, 18 and 5 MBq/kg of body weight. The toxicity of the radionuclide upon inhalation intake is approximately twice as high, which is associated with a larger area of ​​contact beta irradiation. All organs and systems are involved in the pathological process, especially severe damage in the thyroid gland, where the highest doses are formed. The doses of irradiation of the thyroid gland in children due to its small mass when receiving the same amount of radioiodine are much higher than in adults (the mass of the gland in children, depending on age, is 1: 5-7 g, in adults - 20 g). Radioactive Iodine Radioactive iodine contains much more detailed information, which, in particular, may be useful to medical professionals. radioactive cesium Radioactive cesium is one of the main dose-forming radionuclides of uranium and plutonium fission products. The nuclide is characterized by high migratory ability in the environment, including food chains. The main source of radiocesium intake for humans is food of animal and vegetable origin. Radioactive cesium supplied to animals with contaminated feed accumulates mainly in muscle tissue (up to 80%) and in the skeleton (10%). After the decay of radioactive isotopes of iodine, radioactive cesium is the main source of external and internal exposure. In goats and sheep, the content of radioactive cesium in milk is several times higher than in cows. In significant quantities, it accumulates in the eggs of birds. The coefficients of accumulation (excess over the content in water) of 137 Cs in the muscles of fish reaches 1000 or more, in mollusks - 100-700, crustaceans - 50-1200, aquatic plants - 100-10000. The intake of cesium to a person depends on the nature of the diet. So after the Chernobyl accident in 1990, the contribution of various products to the average daily intake of radiocesium in the most contaminated areas of Belarus was as follows: milk - 19%, meat - 9%, fish - 0.5%, potatoes - 46%, vegetables - 7.5%, fruits and berries - 5%, bread and bakery products - 13%. An increased content of radiocesium is recorded in residents who consume large quantities of "gifts of nature" (mushrooms, wild berries, and especially game). Radiocesium, entering the body, is relatively evenly distributed, which leads to almost uniform exposure of organs and tissues. This is facilitated by the high penetrating power of gamma quanta of its daughter nuclide 137m Ba, which is approximately 12 cm. In the original article by I.Ya. Vasilenko, O.I. Vasilenko. Radioactive cesium contains much more detailed information about radioactive cesium, which, in particular, may be useful to medical professionals. radioactive strontium After the radioactive isotopes of iodine and cesium, the next most important element whose radioactive isotopes contribute the most to pollution is strontium. However, the share of strontium in irradiation is much smaller. Natural strontium belongs to microelements and consists of a mixture of four stable isotopes 84Sr (0.56%), 86Sr (9.96%), 87Sr (7.02%), 88Sr (82.0%). According to the physicochemical properties, it is an analogue of calcium. Strontium is found in all plant and animal organisms. The body of an adult contains about 0.3 g of strontium. Almost all of it is in the skeleton. Under the conditions of normal operation of nuclear power plants, releases of radionuclides are insignificant. They are mainly due to gaseous radionuclides (radioactive noble gases, 14 C, tritium and iodine). Under conditions of accidents, especially large ones, releases of radionuclides, including strontium radioisotopes, can be significant. Of greatest practical interest are 89 Sr (T 1/2 = 50.5 days) and 90 Sr (T 1/2 = 29.1 years), characterized by a high yield in the fission reactions of uranium and plutonium. Both 89 Sr and 90 Sr are beta emitters. The decay of 89 Sr produces a stable isotope of yttrium ( 89 Y). The decay of 90 Sr produces beta-active 90 Y, which in turn decays to form a stable isotope of zirconium (90 Zr). C scheme of the decay chain 90 Sr → 90 Y → 90 Zr. The decay of strontium-90 produces electrons with energies up to 546 keV; the subsequent decay of yttrium-90 produces electrons with energies up to 2.28 MeV. In the initial period, 89 Sr is one of the components of environmental pollution in the zones of near fallout of radionuclides. However, 89 Sr has a relatively short half-life and over time 90 Sr begins to predominate. Animals receive radioactive strontium mainly with food and, to a lesser extent, with water (about 2%). In addition to the skeleton, the highest concentration of strontium was noted in the liver and kidneys, the minimum - in the muscles and especially in fat, where the concentration is 4-6 times lower than in other soft tissues. Radioactive strontium belongs to osteotropic biologically hazardous radionuclides. As a pure beta emitter, it poses the main danger when it enters the body. The nuclide is mainly supplied to the population with contaminated products. The inhalation route is less important. Radiostrontium is selectively deposited in the bones, especially in children, exposing the bones and the bone marrow contained in them to constant radiation. Everything is described in detail in the original article by I.Ya. Vasilenko, O.I. Vasilenko. Radioactive strontium.