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1593356239-Biological effects of ionizing radiation. Topic discussion.ppt
- 1. Biological effects of ionizingradiation
- 2. Biological effect of ionizingradiation – the ability of ionizing radiation to cause functional, anatomic and metabolic changes at all levels of biological organization. • Ionizing radiation always has a destructive effect on a living organism!
- 3. Steps of biologicaleffect of ionizing radiation • Ionizing radiation interact with living material and living material absorbs that radiation. • It cause ionization and excitation of atoms and molecules. • It cause primary radiochemical reactions (disruption of molecular associations with formation of free radicals with high chemical activity. • But this is only the direct (primary) effect of radiation!
- 4. • These freeradicals interact with surrounding intact atoms and molecules (proteins, lipids…) and cause their splitting with formation of following free radicals which interact with molecules that are unexposed to rays directly. • This is called indirect (secondary) effect of ionizing radiation, because these changes of molecules emerge not directly from ionizing radiation, but from the energy of molecules, that were changed by ionizing radiation. • During radiation exposure very small amount of molecules of the organism exposed to rays are under direct effect!
- 6. The stages ofradiation defect
- 7. 1. Absorbed doseand power of radiation – BE increases with the growth of them. 2. Distribution of radiation dose in time – distribution of the same total dose into separate fragments leads to diminishing of BE. The processes of renewal begin at once after radiation exposure and are able to compensate, at least partly, the caused violations. Biological effect (BE) depends on:
- 8. 3. Distribution ofradiation dose in the organism: - General radiation exposure (= radiation exposure of the whole organism) – cause greater changes in cells. - Local radiation exposure (= radiation exposure of some part of the organism) – cause smaller changes in cells. - It is also important which part of the body (more or less radiosensitive) is exposed to radiation! 4. Type of radiation – the same dose of different types of ionizing radiation can cause different BE. 5. Personal radiosensitivity of a living organism. Biological effect (BE) depends on:
- 9. 1. Kind ofliving organism. There are specific differences in radiosensitivity of different kinds of living organism: mortal dose for a man is more than 6 Gy, for a rabbit – 12 Gy, for bacteria – hundreds of thousands of Gy… 2. Gender. Males are more radiosensitive than females. 3. Age. Chidren are more radiosensitive than adults and elderly persons. 4. Genetic constitution. Personal radiosensitivity depends on:
- 10. 5. State ofhealth. Patients are usually more radiosensitive than healthy people. 6. Nutrition. People with unbalanced nutrition are more radiosensitive than people with well balanced nutrition. 7. Hormonal status. People with hormonal status violations are more radiosensitive than people with proper hormonal status. Personal radiosensitivity depends on:
- 11. 8. The amountof oxygen in the atmosphere during radiation exposure. “Oxygen effect” – the less is the partial pressure of oxygen, the less is radiation defect. In case of hypoxia, the radiosensitivity of the organism can decrease in 2-3 times. 9. The temperature. A decrease in body temperature below normal levels is accompanied by an increase of radioresistance. Personal radiosensitivity depends on:
- 12. Law of Bergonieand Tribondeau Radiosensitivity of tissues is directly proportional to the proliferative activity and inversely proportional to the degree of differentiation of the cells constituting it. 3 groups of critical organs (depending on their radiosensitivity) Group I (the most sensitive): red bone marrow, gonades, lymphoid tissue. Group II: all organs, that are not included into groups I and III (liver, kidney, spleen, thyroid, lungs, GIT, lens, muscles…). Group III (the least sensitive): skin, bone tissue, hands, forearms, shins, feet.
- 13. - interval oftime which covers the period from the moment of radiation exposure to the appearance of changes which can be registered clinically. The higher the radiation dose, the shorter the latent period! “Latent period” is only clinical concept, because actually BE starts to develop at the moment of radiation exposure! Latent period of biological effect
- 14. 1. Interphase: - presyntheticperiod (G1) - synthetic period (S) – period of synthesis of DNA. - postsynthetic period (G2) 2. Mitosis (M) – the shortest period (30-60 min.) Stages of a cell’s life cycle
- 16. • Temporary suppression(delay) of cellular division. Usually this delay is equal to 1 hour per every 1 Gy. This delay is the longest if radiation exposure was during S period, and the shortest – if it was during M period. • Complete suppression of cellular division – when cell continues to live for a considerable time but completely loses ability to divide. Can occur after higher doses of radiation. Effects of ionizing radiation on cells
- 17. • Reproductive cellulardeath – the loss of proliferation ability by a cell. It is the most widespread form of cellular death after radiation exposure! • Cellular death may occur immediately after radiation exposure during interphase (interphase death), during cell’s attempt to divide (mitotic death) or after a few cell divisions (in case of formation of giant cells). • Giant cells emerge as a result of the confluence of 2 adjacent cells. They are able to divide 2-3 times, after which they die. Types of lethal effects of radiation exposure
- 18. Cell and DNAstructure
- 19. The nature ofcells’ radiation death • The main reason of reproductive cell death at radiation exposure is the damage of their genetic apparatus (nucleus is much more sensitive that cytoplasm). Radiation can cause different changes in DNA: - single breaks of DNA (when associations between separate atomic groups are violated in one of the filaments of a double spiral molecule of DNA) – don’t result in breakages of a molecule of DNA, because they may be restored well enough by system of reparation. Single breaks are not the reasons for cell death. - double breaks of DNA (when a break takes place at once near closely located areas of two filaments) - result in breakages of a molecule of DNA, because they may not be restored well enough by system of reparation. Double breaks can cause cell death. • Damage of cytoplasmic organels – decrease functional activity of cells and can cause remote consequences of radiation exposure.
- 20. Principles of defencefrom ionizing radiation • Defence by amount – diminishing of the sources power up to the minimal values at a workplace. The less activity of source of radiation, the less the dose of radiation exposure! • Defence by time – the reduction of the time of contact with radiation source. The less the time of contact with source of radiation, the less the dose of radiation exposure! • Defence by distance – increase of the distance between people and source of radiation. The greater the distance from source of radiation, the less the dose of radiation exposure! If you double your distance from a source, the dose you receive from the source is 4 times less. • Defence by screen – screening of sources with materials which absorb ionizing radiation.
- 21. Protective means against ionizingradiation effect • Personal – special clothes and footwear, protective means for respiratory organs, additional protective devices… • Collective: walls, ventilation, hermetic equipment…
- 22. Radiotherapeutic interval (RTI) (=the therapeutic interval of radiosensitivity) - the difference between normal and tumor cell radiosensitivity. The greater is this interval, the easier is to obtain tumor destruction with saving the viability of surrounding tissues.
- 23. Ways of increasingof RTI • Changing of radiation exposure rhythm: total dose of radiation exposure is divided into separate parts (fractions). A tumor is exposed to rays repeatedly, by small (2-3 Gy), middle (5-6 Gy) or large (8-12 Gy) fractions. • Dose protraction: each fractioned radiation exposure is prolonged by decreasing of the power of a dose. • Use of radiomodifiers (radiosensibilizators and radioprotectors).
- 24. Types of radiomodifiers 1.Radiosensibilizators – are used to increase tumor radiosensitivity: - saturation of tumor with oxygen (radiation exposure during oxygenotherapy); - hyperthermia; - pharmaceutical preparations, that can increase primary damage of DNA (fluorouracil, methotrexate, heparin), weaken the postradiation renewal of tumor cells (antibiotics of actinomycin group), worsen tumors’ trophic conditions (gexamine). 2. Radioprotectors – are used to reduce normal cell radiosensitivity: - hypoxia (inhalation of a mixture of nytrogen with 12% oxygen, putting a tourniquet on extremity); - hypothermia; - pharmaceutical preparations (serotonine, cystamine).