Dr. Tatyana Lenchuk

Phd

The biological effect of ionizing radiation on the cell (normal and pathologically changed)

Content1.Biological effect of ionizing radiation2.The sources of ionizing radiation3.The properties of ionizing radiation4.The dependence of biological effect of ionizing radiation from the type, dose and energy.5.The characteristics of ionization and excitation6.Mechanism of the influence of ionizing radiation on the living objects7.The levels of metabolic changes in the organism8.Mutagenic ability of radiation9.Individual and specific sensitivity10.The dependence of radiosensitivity from environmental conditions

Radiology consists of radiation genetics, biochemistry, ecology, hygiene, immunology, anti-radiation protection and treatment, cosmic radiology, radiobiology of tumors.

Polluted air leads to respiratory system diseases; Contaminated food and water affects GIT; Pollution of human body surface - skin diseases;

Biological effect of ionizing radiation is the reaction of organism as answer of radiation, which manifests by morphologic, functional, metabolic changes in all the levels of it’s organization: atomic, molecular cellular, tissular, organ and organism.

The source of ionizing radiation is an object, which consists of radioactive material, technical device that can radiate (in certain condition) ionizing radiation. There are natural and artificial sources of radiation. Natural: space form (background -protons, neutrons, nucleus of atoms has comparatively high energy decreased with the presence of atmosphere. Low on Earth's surface.

Artificial devices made by humans. X-ray tubes, radioactive nuclides are formed in nuclear reactors, generators and charged particle accelerators.

 

Ionizing radiation by nature is divided into corpuscular and photon. And also primarily and secondary ionizing.

Corpuscular (fast moving): electrons, protons, α-particles, neutrons

Photon – gamma and X-rays. These are electromagnetic waves. The are the energy which is spreading without movement of matter (like optical and thermal wave). These waves are similar by their characteristics. But X-rays are formed by slowdown of electrons, which were accelerated in electric field of X-ray tube, and gamma-rays are formed by conversion of excited nucleuses of atoms into neutral. Electromagnetic IR is secondary ionizing. Part of it’s energy is converting into kinetic energy of electrons, which were pushed from their orbits, and they act as active β-particles.

The main ways of radionuclide entering into the organism

Air pollution

Food and water

pollutionContaminatio

n of the human skin

Contamination of wounds

Through the

respiratory system

Through the digestive

tractThrough the skin

Through the

wounds

Blood and lymph

Accumulation of radionuclides in

organs and tissues

The artificial sources of ionizing radiation used in medicine

Radioactive substances Accelerators of the charged particles

Sealed Unsealed Linear

Cyclic Roentgen devices

Gamma-therapeutical devices

Radioactive medications

Solutions

Suspensions

CyclotronBetatron

Synchrophasotron

Teletherapy

Static

Brachytherapy

Static Dynamic

1. Tubes2. Balls3. Needle

s4. Darts5. Plastic

masses

UsualColloid

MacroMicro

Characteristics of ionizing radiation:

1. Ability to penetrate through the large and thick objects (not transparent)2. Ionize air and molecules of living organisms. It is because of it’s energy (energy of light 0.5 eV, α-particle 10MeV-ionizing ability 20.000 pairs of ions/mm-maximal ionizing effect and biological influence)3. Ability to activate photo materials in dosimetry4. Scintillation5. Ability to accumulate and cause distant effects (malignant tumors, genetic mutations)6. We don’t feel the radiation7. Ionizing radiation is spreading linearly, causing interferention and refraction

  

Type of radiation

EnergyMeV

VelocityKm/h

Length of the run in air

Length of the run in tissues

Ionizing abilityPairs/mm

4+2He 1-10 20000 <20cm <50 mcm 10000-20000

0 -+1 β 0.1-2 270000 <15m <1 cm 5-10

γ 0.1-20 300000 >100m >10 cm 1 p/cm

First stage of ionizing radiation: physical process of the interactions between the radiation and substance as a result of this interaction, we have excited and ionized atoms and molecules that have high chemical activity. They interact between each other and with surrounding atoms, in this case a large amount of highly active free radicals and peroxides appear. The ionization is the separation of the electron from atom. If the energy (E) given to the atom is not enough to separate the electrons, this electron changes its position to the outer orbit and becomes excited.

Second stage, radiation and chemical process which leads to the charge of the structure of molecules and as a result to the biochemistry of cell disorders. Radiolysis -formation of free radicals, which are highly active because they have an insufficient number of electrons. Chain reaction. The larger the molecule, the higher its ability to be ionized. Process of inactivation of enzymes -OH groups, SH-groups come together.

Water radiolysis

Н2О Н2О+ + e Н2О+ + Н2О Н3О+ + ОН*

Н2О+ + e Н2О* Н* і ОН*

Н* + О2 НО2*

НО2* + НО2

* Н2О2 + 2О

Tissue: The most sensitive are highly proliferating tissues like lymphoid, haemopoietic, endocrine. They die at a low 0-4 Gy. It causes anemia, leucopoenia, and other disorders. The lower radioactive lesions, which occur in the future, are in the tissues, which have lower proliferative ability (bones, cartilage, muscles, fat). They die at the dose of 30-100 Gy.

Organ level: The most sensitive organs/systems: digestive tract, small intestine. The least sensitive is liver. The organs, which are most sensitive, are called "critical" organs. The critical organs, which are all important for the organism: nervous system, bone marrow, in the case of injury can cause death. Results of ionizing radiation can be separated into:

Changes in somatic cells-cause malignizationGenetic mutations- affect the future generationAffect on the embryo and fetus in case of

pregnant women radiationDeath during radiation

The direct effect of ionizing radiation - cases where radiation directly causes changes: ionization, excitation, radiolysis of water and the formation of radicals. The direct effect of radiation because the radiation of cell damage is the result of the direct effects of ionizing particles or γ-quantum is particularly sensitive to the amount of cells, primarily in the nucleus, resulting in its inactivation and destruction. It could be other cell organelles.t.

Indirect ( mediated ) effect of ionizing radiation - when fragments of molecules, oxidizing radicals OH, H2O2, HO2 ions , the primary lipid peroxidation radiotoxins type , quinones interact with intact molecules , joining them and changing their structure and properties. Oxidative radical steps are easy to sulfhydryl groups of enzymes and DNA. This can cause them to rupture not contain attachment, and the other two to form active radicals. As a result of possible chain reaction . For example, disintegrated molecule 1 and 2 was formed radicals. They interact with two intact molecules, which in turn break down into 4 radicals , etc. Therefore, a small amount of primary energy is so great effects in the body. This is a physical, chemical and biochemical level damage. These processes occur in the cells , tissues and organs.

So functional and morphological changes in the cells of a living organism that occur under the influence of ionizing radiation can be caused by two mechanisms:

         direct action of radiation / - ionization and excitation of atoms and molecules irradiated cells of the body / and indirectly - influence of radicals formed in the area of exposure.

Speaking about the mechanism of the indirect effects of ionizing radiation, it must be emphasized that the radiation response of water is largely dependent on the content of oxygen . Established that lack of oxygen is important in the direct irradiation, ie at the time when the formation of free radicals and there . Lack of oxygen or decrease its partial pressure in the tissues reduces the effectiveness of ionizing radiation. Thus , the degree of radiation reactions depends on the concentration of oxygen in a biological substrate. This phenomenon is known in radiobiology "called oxygen effect .

Examining the relationship between dose and effect of biological, be aware that the smaller the dose of ionizing radiation, the later clinical manifestations may occur biological effect, they are often 30-40 years after the exposure .

With increasing doses, increases the degree of biological effect, reduced the timing of its discovery, however, may change the quality of the effect. Increasing the degree of biological effect with increasing dose proportionally occurs only in certain ranges of doses.

The least sensitive to ionizing radiation and bacteria are simple, the most sensitive - mammals. In a nuclear reactor, where the dose reached 10 million in the glad day, were discovered bacteria that not only killed by the powerful radiation flux, but divided, multiplied, Different radiosensitivity and radiostiykistyu have not only different kinds of organisms, but animals of one species. This difference is already for the minimum, average and absolute lethal doses. After all these experiments matched animals of the same sex, age and weight. People are also inherent in the individual radiosensitivity. It is well known radiation therapist. Some patients tolerate the entire course of treatment without any complications, but other radiation reactions begin just after the first session of radiotherapy.and "feel" great.

Important role to play radiosensitivity overall health and his age. The most radiosensitive organisms in the embryonic period, especially during the active bookmarks organs in humans - in 2-6 weeks after conception, that is when a pregnancy may be not yet installed. The dose is harmless for the mother, can cause serious violations of fetal development. Young organisms are more radiosensitive and after birth. Therefore, exposure of young women and children are allowed only in cases of emergency.

.

Many years of experimental and clinical studies make it possible schematic classification of radiosensitivity of normal cells and tissues by decreasing the degree on the basis of radiation damages. The high radiosensitivity have: embryonic, lymphatic tissue, spleen, thymus gland, RE system, testes, ovaries, bone marrow, small intestine, where the first signs of damage are observed at a dose of 25-100 x-rays, and severe lesions - a dose of 400-600 x-ray.

Average, radiosensitivity was found in the skin, mucous membranes, eyes, growing bones, cardiovascular system, to achieve serious injuries they needed dose 850-2000 x-rays, and the first signs appear at a dose of 300-800 x-rays,?

The low radiosensitivity own tissue endocrine secretions, liver, kidney, ts.n.c., lung, skeletal and smooth muscle of the heart. The minimum dose that causes certain defeat - 1000 - 4000 X-ray, severe lesions arise from 3000-6000 X-ray radiation

RadiotherapyThe medical use of ionizing radiation as art of

cancer treatment to control malignant tumors. It's for curative cancer treatment or as a pain alleviating treatment. It's also used as a therapeutic treatment. Total body irradiation — a technique used to prepare the body to receive a bone marrow transplant. To spare normal tissues, shaped radiation beams are aimed from different angles of exposure to interact at the tumor, providing a larger absorbed dose than in the surrounding healthy tissue.

Side -effects: Acute (arising during treatment) cause damage to epithelial surfaces. Edema- swelling of soft tissues may cause problems during radiotherapy. Surgical intervention may be considered prior to treatment or steroids may be used during radiotherapy to reduce swelling.

Infertility (gametes won't be produced after direct exposure of gonads to most normal doses). And also generalized fatigue.

Medium and long-term side effects. It depends on tissue being treated. Fibrosis—tissue becomes less elastic over time due to a diffuse scarring process. Hair loss-radiation induced is more likely to be permanent, limited to the area of treatment. Dryness-xerostomia and xerophalmia, dryness of vaginal mucosa after pelvic irradiation. Cancer-secondary malignancy seen in a minority of patients.