Radiobiology PDF 2023-2024

1 Radiobiology /Lec.2/1 rd Stage/Department sonar and rays /Ibn khaldun university /Laith Fawzi/2023-2024 Types of Cellular Damage due to radiation Whether the source of radiation is natural or man-made, whether it is a small dose of radiation or a large...

1 Radiobiology /Lec.2/1 rd Stage/Department sonar and rays /Ibn khaldun university /Laith Fawzi/2023-2024 Types of Cellular Damage due to radiation Whether the source of radiation is natural or man-made, whether it is a small dose of radiation or a large dose,there will be some biological effects. Radiation Causes Ionizations of: ATOMS which may affect MOLECULES which may affect CELLS which may affect TISSUES which may affect ORGANS which may affect THE WHOLE BODY. Cellular damage Even though all subsequent biological effects can be traced back to the interaction of radiation with atoms, there are two mechanisms by which radiation ultimately affects cells. These two mechanisms are commonly called direct and indirect effects. 1- Direct Effect: If radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell, it is referred to as a direct effect. Such an interaction may affect the ability of the cell to reproduce and, thus, survive. If enough atoms are affected such that the chromosomes do not replicate properly, or if there is significant alteration in the information carried by the DNA molecule, then the cell may be destroyed by “direct” interference with its life-sustaining system. 2- Indirect Effect: If a cell is exposed to radiation, the probability of the radiation interacting with the DNA molecule is very small since these critical components make up such a small part of the cell. However, each cell, just as is the case for the human body, is mostly water. Therefore, there is a much higher probability of 1 2 radiation interacting with the water that makes up most of the cell’s volume. When radiation interacts with water, it may break the bonds that hold the water molecule together, producing fragments such as hydrogen (H) and hydroxyls (OH). These fragments may recombine or may interact with other fragments or ions to form compounds, such as water, which would not harm the cell. However, they could combine to form toxic substances, such as hydrogen peroxide (H2O2), which can contribute to the destruction of the cell. Radiation Effects on Cells & DNA: What is DNA? Every one of your cells contains deoxyribonucleic acid (DNA). This important molecule is like your body’s instruction manual. It constantly tells your cells what to do and how to do it. Every living organism has DNA in all of its cells. A DNA molecule is built like a twisted ladder. The long rails are made of sugar and phosphate molecules. These are called the “backbone” of a DNA molecule. Each rung is a combination of four nucleotide bases. These are adenine, guanine, cytosine, and thymine. Each nucleotide has a letter that represents it. “A” stands for adenine, “G” for guanine, “C” for cytosine and “T” for thymine. 2 3 How does direct action affect DNA? Ionizing radiation can interact directly with a DNA molecule’s atoms. This prevents cells from reproducing. Direct action can also damage critical cellular systems. Sometimes, it can even lead to cancer. Alpha particles, beta particles and X-rays can directly affect a DNA molecule in one of three ways: 1- Changing the chemical structure of the bases. 2- Breaking the sugar-phosphate backbone. 3- Breaking the hydrogen bonds connecting the base pairs. How does indirect action affect DNA? Ionizing radiation can also affect important molecules other than DNA. For example, it can break the bonds holding water molecules together. This creates hydrogen (H+) and hydroxyls (OH-) ions. These are called free radicals. 3 4 What is ionizing radiation? Ionizing radiation is radiation that can remove electrons from an atom. Losing an electron charges, or ionizes, the atom. Sometimes, ionizing radiation takes the form of a wave, like gamma rays or X-rays. But it can also take the form of a particle, like neutrons or alpha and beta particles. You are surrounded by ionizing radiation. The Earth has always been home to radioactive materials. Here are some natural sources of ionizing radiation:  Space (cosmic radiation)  The ground (terrestrial radiation)  Air  Water  Food How does ionizing radiation affect cells? When ionizing radiation interacts with a cell, several things can happen: 1- The radiation could pass through the cell without damaging the DNA. 2- The radiation could damage the cell’s DNA, but the DNA repairs itself. 3- The radiation could prevent the DNA from replicating correctly. 4- The radiation could damage the DNA so badly that the cell dies. 4 5 Cellular Sensitivity to Radiation: (from most sensitive to least sensitive) Lymphocytes and Blood Forming Cells Reproductive and Gastrointestinal (GI) Cells Nerve and Muscle Cells. Not all living cells are equally sensitive to radiation. Those cells which are actively reproducing are more sensitive than those which are not. This is because dividing cells require correct DNA information in order for the cell’s offspring to survive. A direct interaction of radiation with an active cell could result in the death or mutation of the cell, whereas a direct interaction with the DNA of a dormant cell would have less of an effect. As a result, living cells can be classified according to their rate of reproduction, which also indicates their relative sensitivity to radiation. This means that different cell systems have different sensitivities. Lymphocytes (white blood cells) and cells which produce blood are constantly regenerating, and are, therefore, the most sensitive. Reproductive and gastrointestinal cells are not regenerating as quickly and are less sensitive. The nerve and muscle cells are the slowest to regenerate and are the least sensitive cells. Repair damage: Cells, like the human body, have a tremendous ability to repair damage. As a result, not all radiation effects are irreversible. In many instances, the cells are able to completely repair any damage and function normally. 5 6 If the damage is severe enough, the affected cell dies. In some instances, the cell is damaged but is still able to reproduce. The daughter cells, however, may be lacking in some critical life- sustaining component, and they die. The other possible result of radiation exposure is that the cell is affected in such a way that it does not die but is simply mutated. The mutated cell reproduces and thus perpetuates the mutation. This could be the beginning of a malignant tumour. Organ Sensitivity: (from most sensitive to least sensitive) Blood Forming Organs Reproductive and Gastrointestinal Tract Organs, Skin Muscle and Brain. The sensitivity of the various organs of the human body correlate with the relative sensitivity of the cells from which they are composed. For example, since the blood forming cells were one of the most sensitive cells due to their rapid regeneration rate, the blood forming organs are one of the most sensitive organs to radiation. Muscle and nerve cells were relatively insensitive to radiation, and therefore, so are the muscles and the brain. Radiation Effects: -High Doses (Acute) -Low Doses (Chronic) Biological effects of radiation are typically divided into two categories. The first category consists of exposure to high doses of radiation over short periods of time producing acute or short- term effects. The second category represents exposure to low doses of radiation over an extended period of time producing chronic or long-term effects. High doses tend to kill cells, while low doses tend to damage or change them. High doses can kill 6 7 so many cells that tissues and organs are damaged. This in turn may cause a rapid whole-body response often called the Acute Radiation Syndrome (ARS). Low doses spread out over long periods of time don’t cause an immediate problem to any body organ. The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years. High Dose Effects: Dose (Rad) Effect Observed 15 - 25 Blood count changes in a group of people 50 Blood count changes in a group of people 100 Blood count changes in an individual 150 Vomiting (threshold) 320 - 360 Death (threshold) 480 – 540 LD 50/60 with minimal care 1,100 LD 50/60 with supportive medical care Every acute exposure will not result in death. If a group of people is exposed to a whole-body penetrating radiation dose, the above effects might be observed. The information for this table was extracted from NCRP Report No. 98, Guidance on Radiation Received in Space Activities, 1989.In the above table, the threshold values are the doses at which the effect is first observed in the most sensitive of the individuals exposed. The LD 50/60 is the lethal dose at which 50% of those exposed to that 7 8 dose will die within 60 days. It is sometimes difficult to understand why some people die while others survive after being exposed to the same radiation dose. The main reasons are the health of the individuals at the time of the exposure and their ability to combat the incidental effects of radiation exposure, such as the increased susceptibility to infections. Other High Dose Effects: Skin Burns, Hair Loss,Sterility,Cataracts. Besides death, there are several other possible effects of a high radiation dose.Effects on the skin include erythema (reddening like sunburn), dry desquamation (peeling), and moist desquamation (blistering). Skin effects are more likely to occur with exposure to low energy gamma-ray, or beta radiation. Most of the energy of the radiation is deposited in the skin surface. The dose required for erythema to occur is relatively high, in excess of 300 rad. Blistering requires a dose in excess of 1,200 red-haired loss, also called epilation, is similar to skin effects and can occur after acute doses of about 500 rad. Sterility can be temporary or permanent in males, depending upon the dose. In females, it is usually permanent, but it requires a higher dose. To produce permanent sterility, a dose in excess of 400 rad is required to the reproductive organs. Cataracts (a clouding of the lens of the eye) appear to have a threshold of about 200 rad. Neutrons are especially effective in producing cataracts, because the eye has a high-water content, which is particularly effective in stopping neutrons. Categories of Effects of Exposure to Low Doses of Radiation: Genetic, Somatic ,In-Utero. There are three general categories of effects resulting from exposure to low doses of radiation. These are: 8 9 Genetic - The effect is suffered by the offspring of the individual exposed. Somatic - The effect is primarily suffered by the individual exposed. Since cancer is the primary result, it is sometimes called the Carcinogenic Effect. In-Utero - Some mistakenly consider this to be a genetic consequence of radiation exposure, because the effect, suffered by a developing embryo/fetus, is seen after birth. However, this is actually a special case of the somatic effect, since the embryo/fetus is the one exposed to the radiation. GOOD LUCK 9