Radiation Protection PDF

Ibn Khaldoun University College M.Sc. Mustafa Majid Ibrahim Radiation Protection Department of Radiology and Ultrasound Technologies Assistant lecturer/ Mustafa M. Ibrahim third Class / third Lecture: Deterministic Effects of ionizing radiation 1- Acute Radiation Leth...

Ibn Khaldoun University College M.Sc. Mustafa Majid Ibrahim Radiation Protection Department of Radiology and Ultrasound Technologies Assistant lecturer/ Mustafa M. Ibrahim third Class / third Lecture: Deterministic Effects of ionizing radiation 1- Acute Radiation Lethality. Acute radiation lethality refers to a set of lethal effects that occur as a result of exposure to high doses of ionizing radiation over a short period. These doses are typically much higher than those used in diagnostic medical applications. Mechanism: High doses of radiation cause severe damage to cells, especially those that rapidly divide, such as bone marrow cells, gastrointestinal lining cells, and blood cells. Exposure to radiation leads to the destruction of these cells, resulting in organ failure and a significant decrease in blood cell counts. Effects of Acute Radiation Lethality: a- Acute Radiation Syndrome (ARS) b- Bone Marrow Failure c- Gastrointestinal Damage d- Neurological Effects 2- Local Tissue Damage. When only part of the body is irradiated, in contrast to whole-body irradiation, a higher dose is required to produce a response. Every organ and tissue of the body can be affected by partial-body irradiation. The effect is cell death, which results in shrinkage of the organ or tissue. This effect can lead to total lack of function for that organ or tissue, or it can be followed by recovery. 3- Effects on the Skin. The tissue with which we have had the most experience is the skin. Normal skin consists of three layers: an outer layer (the epidermis), an intermediate layer of connec tive tissue (the dermis), and a subcutaneous layer of fat and connective tissue. The skin, similar to the lining of the intestine, repre sents a continuing cell renewal system, only with a much slower rate than that experienced by intestinal cells. Almost 50% of the cells lining the intestine are replaced every day, but skin cells are replaced at the rate of only approximately 2% per day. In earlier times the tolerance of the patient’s skin determined the limitations of radiation oncology with orthovoltage x-rays (200–300 kVp x- rays). The object of x-ray therapy was to deposit energy in the tumor while sparing the surrounding normal tissue. Because the x-rays had to pass through the skin to reach the tumor, the skin was Radiation protection Page 1  Ibn Khaldoun University College M.Sc. Mustafa Majid Ibrahim necessarily subjected to higher radi ation doses than the tumor. The resultant skin damage was seen as erythema (a sunburn-like reddening of the skin) followed by desqua mation (ulceration and denudation of the skin), which often required interruption of treatment. 4- Effects on the Gonads Human gonads are critically important target organs. As an example of local tissue effects, they are particu larly sensitive to radiation. Responses to doses as low as 100 mGyt (10 rad) have been observed. Because these organs produce the germ cells that control fertility and heredity, their response to radiation has been studied extensively. The cells of the testes (the male gonads) and the ovaries (the female gonads) respond differently to radia tion because of differences in progression from the stem cell to the mature cell. 5- Hematologic Effects If you were a radiologic technologist in practice during the 1920s and the 1930s, you might have visited the hematology laboratory once a week for a routine blood examination. Before the introduction of person nel radiation monitors, periodic blood examination was the only monitoring performed on x-ray and radium workers. This examination included total cell counts and a white blood cell (leukocyte) differential count. Most institutions had a radiation safety regulation such that, if the leukocytes were depressed by greater than 25% of normal level, the employee was given time off or was assigned to nonradiation activities until the count returned to normal. What was not entirely understood at that time was that the minimum whole-body dose necessary to produce a measurable hematologic depression was approxi mately 250 mGyt (25 rad). These workers were being heavily irradiated by today’s standards. Cytogenetic Effects: A technique developed in the early 1950s contributed enormously to human genetic analysis and radiation genetics. The technique calls for a culture of human cells to be prepared and treated so that the chromosomes of each cell can be easily observed and studied. This has resulted in many observations on radiation-induced chromosome damage. induced and that some aberrations may be specific to radiation. The rate of induction of chromosome aber rations is related in a complex way to the radiation dose and differs among the various types of aberrations. Attempts to measure chromosome aberrations in patients after diagnostic x-ray examination have been largely unsuccessful. However, some studies involving high-dose fluoroscopy have shown radiation- induced chromosome aberrations soon after the examination was performed. Without question, high doses of radiation cause chro mosome aberrations. Low doses no doubt also do so, but it is technically difficult to observe aberrations at doses that are less than approximately 100 mGyt (10 rad). An even more difficult task is to identify the link between radiation-induced chromosome aberra tions and latent illness or disease. When the body is irradiated, all cells can sustain cytogenetic damage. Such damage is classified here as an early response to radiation because, if the cell sur vives, the damage is manifested during the next mitosis after the radiation exposure. Radiation protection Page 2  Ibn Khaldoun University College M.Sc. Mustafa Majid Ibrahim Human peripheral lymphocytes are most often used for cytogenetic analysis, and these lymphocytes do not move into mitosis until stimulated in vitro by an appro priate laboratory technique. Cytogenetic damage to the stem cells is sustained immediately but may not be manifested for the 1- Normal Karyotype Radiation exposure can lead to various chromosomal changes in the karyotype, which may result in genetic mutations and increase the risk of diseases. a- Chromosomal Breakage Ionizing radiation can cause direct damage to the DNA within chromosomes, leading to breaks in the chromatid. b- Chromosomal Rearrangements Translocations: Segments of one chromosome break off and attach to another chromosome, potentially disrupting gene function. Inversions: A segment of a chromosome breaks off, flips, and reattaches, altering the gene sequence. c- Aneuploidy The presence of an abnormal number of chromosomes in a cell. Like Conditions like Down syndrome (trisomy 21) result from an extra chromosome. 2- Single-Hit chromosome aberrations When radiation interacts with chromosomes, the inter action can occur through direct or indirect effect. In either mode, these interactions result in a hit. The hit, however, is somewhat different from the hit described previously in radiation interaction with DNA. The DNA hit results in an invisible disruption of the molecular structure of the DNA. A chromosome hit, on the other hand, produces a visible derangement of the chromosome. Because the chromosomes contain DNA, this indicates that such a hit has disrupted many molec ular bonds and has severed many chains of DNA. 3- Multi-Hit chromosome aberrations a.Multi-Hit: This refers to the concept that the development of cancer or other diseases often requires multiple genetic mutations or changes within cells. Instead of a single mutation being sufficient, several "hits" or sequential genetic alterations are typically needed to transform normal cells into cancerous ones. b.Chromosome Aberrations: This term means changes in the number or structure of chromosomes. These aberrations can result from errors during cell division and can lead to a variety of health issues, including cancer. Radiation protection Page 3  Ibn Khaldoun University College M.Sc. Mustafa Majid Ibrahim Overall, the relationship between these terms lies in how multiple changes in chromosomes contribute to disease development, such as cancer, where a combination of several aberrations is necessary to achieve the full effect. As shown in the figure 1. Fig.1.Shown the multi-hit chromosome aberrations. 4- Kinetics of Chromosome Aberration The kinetics of chromosome aberration refers to the study of the rate and mechanism by which structural changes in chromosomes occur, often due to environmental factors like radiation, chemicals, or biological processes. Types of Chromosome Aberrations: Structural Aberrations: Includes deletions, duplications, inversions, and translocations. Numerical Aberrations: Changes in chromosome number, such as aneuploidy (loss or gain of chromosomes). Mechanisms of Induction: Radiation: Ionizing radiation can cause double-strand breaks, leading to improper repair and aberrations. Dose-Response Relationship: The incidence of chromosome aberrations often correlates with the dose of radiation or chemical exposure, following a threshold or linear model depending on the agent. Radiation protection Page 4