Chapter 8 Early Radiation Effects on Organ Systems Early Effects Biologic effects of radiation that occur relatively soon after humans receive high doses of ionizing radiation Evidence of such effects comes from numerous laboratory animal studies and data from observation of some irradiated human populations Not common in diagnostic imaging Produced by a substantial dose of ionizing radiation SOMATIC AND GENETIC DAMAGE FACTORS Amount of biologic damage a
human undergoes as a result of radiation exposure depends on several factors. Ionizing radiation produces the greatest amount of biologic damage in the human body when a large dose of densely ionizing (high-LET) radiation is delivered to a large or radiosensitive area of the body. SOMATIC EFFECTS Biologic damage sustained by living organisms (such as humans) as a consequence of exposure to ionizing radiation
Depending on the length of time from the moment of irradiation to the first appearance of symptoms of radiation damage, the effects are classified as either Early somatic effects Nonstochastic (deterministic) somatic effects Late somatic effects Stochastic (probabilistic) somatic effects Early Nonstochastic (Deterministic) Somatic Effects Appear within minutes, hours, days, or weeks of the time of radiation exposure Require a substantial dose of ionizing radiation Do not usually occur in diagnostic imaging
High-dose effects include nausea, fatigue, erythema, epilation, blood disorders, intestinal disorders, fever, dry and moist desquamation, depressed sperm count in the male, temporary or permanent sterility in the male and female, and injury to the central nervous system (at extremely high radiation doses) Whole-body dose of 6 Gy (600 rad) can result in many of these manifestations or organic damage occurring in succession (acute radiation syndrome) Acute Radiation Syndrome (ARS) Radiation sickness Occurs in humans after whole-body reception of large doses of ionizing radiation delivered over a short period of time
Epidemiologic studies of human populations exposed to doses of ionizing radiation sufficient to cause ARS Atomic bomb survivors of Hiroshima and Nagasaki Marshall Islanders inadvertently subjected to high levels of fallout during an atomic bomb test in 1954 Nuclear radiation accident victims such as those injured in the 1986 Chernobyl disaster Radiation therapy patients Symptoms of Acute Radiation Syndrome ARS is a collection of symptoms associated with high-level radiation exposure Three dose-related syndromes occur as part of
the total-body syndrome Hematopoietic syndrome Gastrointestinal syndrome Cerebrovascular syndrome Major Response Stages of ARS ARS presents in four major response stages Prodromal, or initial, stage Latent period Manifest illness
Recovery or death FIGURE 7-4 The graph depicts the stages of acute radiation syndrome following whole-body reception of large doses of ionizing radiation delivered over a short period of time. The length of time involved for the syndrome to run its course and the final outcome of the syndrome depend on the dose received. (From Radiobiology and radiation protection: Mosbys radiographic instructional series, St Louis, 1999, Mosby.) Acute Radiation Syndrome as a Consequence of the Chernobyl Nuclear Power Plant Accident Location of nuclear power plant Date of accident Description of events Use of biologic criteria in the identification of radiation
casualties during the first two days after the accident Impact of accident on workers, firefighters, and local residents Doses of ionizing radiation received Dose assessment as determined from biologic dosimetry FIGURE 1-13 A, Nuclear power plant in Chernobyl, former Soviet Union, site of the 1986 radiation accident. B, Aerial view of the four identical units of the Chernobyl nuclear power plant before the accident. Graphics point out each of the reactors. C, Chernobyl nuclear power plant after the explosion of unit 4 on April 26, 1986. (A, Courtesy Ken Graham Photography; B and C, courtesy U.S. Department of Energy.) Acute Radiation Syndrome as a Consequence of the Atomic Bombing of Hiroshima and Nagasaki Human population affected by ARS as a consequence of
war Follow-up studies of survivors demonstrating late deterministic and stochastic effects of ionizing radiation Awareness of the need for a thorough understanding of ARS and appropriate medical support of persons affected Forms of Acute Radiation Syndrome Three forms of ARS Hematopoietic syndrome (bone marrow syndrome) Dose range of ionizing radiation Damage to the human body Outcome Gastrointestinal syndrome
Dose range of ionizing radiation Damage to the human body Outcome Cerebrovascular syndrome Dose range of ionizing radiation Damage to the human body Outcome Overview of Acute Radiation Lethality Lethal Dose (LD) LD 50/30 Signifies the whole/body dose of radiation that can be lethal
to 50% of the exposed population within 30 days Quantitative measurement that is fairly precise when applied to experimental animals LD 50 for humans may require more than 30 days for its full expression For adult humans the 7-6 LD 50/30 refers to the whole-body dose of radiation estimated dose is 3.0 to 4.0 Gy FIGURE that can be lethal to 50% of the exposed population within 30 days. As can be seen in the graph, no deaths are expected below (300 to 400 rad) 1 Gy (100 rad). In this particular graph, which represents human response to radiation exposure, LD 50/30 is reached at 3.5 Gy (350 rad), a dose that falls between 3.0 and 4.0 Gy (300-400 rad). This is the point at which half of those exposed to 3.5 Gy
(350 rad) of ionizing radiation would die. The graph also demonstrates that a dose of 6 Gy (600 rad) no one is expected to survive. In reality, survival is possible with extensive medical intervention. Repair and Recovery Cells contain repair enzymes in their biochemistry, enabling them to possibly repair and recover when they are exposed to sublethal doses of ionizing radiation. After irradiation, surviving cells begin to repopulate. This permits an organ that has sustained functional damage as a result of radiation exposure to regain some or most of its functional ability. The amount of functional damage sustained determines the organs potential
for recovery. In the repair of sublethal damage, oxygenated cells receiving more nutrients have a better prospect for recovery than do hypoxic cells receiving fewer nutrients. Repeated radiation injuries have a cumulative effect. About 10% of radiation damage is irreparable, whereas the remaining 90% may be repaired over time. Local Tissue Damage A response can occur when any part of the human body receives a high radiation dose. Cell death results after such a substantial partial-body exposure. This leads to atrophy of organs and tissues.
Result: Organs and tissues sustaining such damage may lose their ability to function, or they may possibly recover. Recovery may be partial or complete, depending on the type of cells involved and the dose of radiation received. If no recovery occurs, necrosis, or death, of the irradiated biologic structure results. Organ and tissue response to radiation exposure depends on Radiosensitivity Reproductive characteristics Growth rate The Skin Three layers of the skin Epidermis (outer layer) Dermis (middle layer) Hypodermis (subcutaneous layer)
Accessory structures include Hair follicles Sensory receptors Sebaceous glands Sweat glands FIGURE 7-7 Layers of the skin and accessory structures. (From Thibodeau GA, Patton KT: Anatomy and physiology, ed 6, St Louis, 2007, Mosby.) Effects of Ionizing Radiation on the
Skin Radiation-induced skin damage Radiodermatitis Cancerous lesions Radiation-induced skin damage Desquamation Historical evidence Historical evidence FIGURE 3-5 Lesions of the fingers induced by ionizing radiation. (Courtesy Ken Bontrager.)
FIGURE 7-2 Dry and moist desquamation. The back of this female Japanese atomic bomb survivor demonstrates the pattern of the kimono she was wearing at the time of the bombing. Radiation burns resulting in the shedding of the outer layer of skin are visible. (From PhotoAssist, Inc.) Effects of Ionizing Radiation on the Skin Radiation-induced skin damage Epilation (alopecia) Moderate doses of radiation may result in temporary hair loss Large doses of radiation may result in permanent hair loss Historical evidence of treating skin diseases such as ringworm Grenz rays Orthovoltage radiation therapy treatment
Cardiovascular or therapeutic interventional procedures that use high-level-fluoroscopy for extended periods of time Development of the Male and Female Germ Cells FIGURE 7-8 Development of the germ cell from the stem cell phase to the mature cell. Effects of Ionizing Radiation on the Reproductive System Radiosensitivity of human germ cells Gonadal dose that can depress the male sperm population or cause a genetic mutation in future generations Gonadal dose that may delay or suppress menstruation in the female Differences in the way the testes of the male and the ovaries of the female respond to ionizing radiation exposure Gonadal dose of ionizing radiation that will cause temporary
sterility in the male and in the female Gonadal dose of ionizing radiation that will cause permanent sterility in the male and in the female Hematologic Effects Current status of relying on hematologic depression as a means for monitoring imaging personnel to assess whether they have sustained any degree of radiation damage from occupational exposure Practice of requiring periodic blood counts for monitoring radiation damage Whole-body dose of ionizing radiation that would produce a measurable hematologic depression Consequences of hematologic depression for the human body
Use of personnel dosimeters for monitoring of occupational exposure Hematopoietic System Bone marrow, circulating blood, and lymphoid organs comprise this system. Cells of this system all develop from a single precursor cell, the pluripotential stem cell. Radiosensitivity of lymphocytes, neutrophils, granulocytes, thrombocytes (platelets), and erythrocytes.
FIGURE 7-9 Progressive development of various cells from a single pluripotential stem cell. Cytogenetic Effects Cytogenetics is the study of cell genetics with emphasis on cell chromosomes. A cytogenetic analysis of chromosomes may be accomplished through the use of a chromosome map called a karyotype. This map consists of a photograph, or photomicrograph.
Metaphase is the phase of cell division in which chromosome damage caused by radiation exposure can be evaluated. FIGURE 7-10 A photomicrograph of the human cell nucleus at metaphase showing each chromosome individually demonstrated. The karyotype is constructed by cutting out the individual chromosomes and paring them with their sister chromosomes. These chromosome pairs are usually aligned by size beginning with the largest pair and ending with the smallest pair. The left karyotype is male, the right is female. (Courtesy Carolyn Caskey Goodner, Identigene, Inc.)
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