1. Early Radiation Effects on Organ Systems
Chapter 8
Early Radiation Effects on Organ Systems

2. 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

3. 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.

4. 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

5. 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)

6. 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 Chernobyl disaster
▬ Radiation therapy patients

7. 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

8. 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: Mosby’s radiographic instructional series, St Louis, 1999, Mosby.)
See

9. 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
Dose assesment was determined from biologic dosimtry
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, (A, Courtesy Ken Graham Photography; B and C, courtesy U.S. Department of Energy.)

10. 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

11. 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
▬ Cerebrovascular syndrome

12. Overview of Acute Radiation Lethality

13. 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 estimated dose is 3.0 to 4.0 Gy (300 to 400 rad)
FIGURE 7-6 LD 50/30 refers to the whole-body dose of radiation 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 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 ( 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.

14. 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 organ’s 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.

15. 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

16. The Skin Three layers of the skin Accessory structures include
▬ 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.)

17. Effects of Ionizing Radiation on the Skin
Radiation-induced skin damage
▬ Radiodermatitis
▬ Cancerous lesions
▬ Historical evidence
Radiation-induced skin damage
▬ Desquamation
▬ 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.)

18. 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

19. 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.

20. 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

21. 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

22. 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.

23. 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.)