Chapter 9: Stochastic Effects and Late Tissue Reactions of Radiation in Organ Systems Flashcards
1
Q
Radiation-induced damage at the cellular level may lead to measurable somatic and hereditary damage in the living organism as a whole later in life
A
Late effects
2
Q
examples of measurable delayed biologic damage are:
A
- Cataracts
- Leukemia
- Genetic mutations
3
Q
are the long-term results of radiation exposure
- months and years later
A
late effects
4
Q
Cataracts are considered to be a
A
late tissue reaction that is nonrandom
5
Q
whereas leukemia and genetic mutations are viewed as
A
delayed stochastic or random consequences that, if these reactions do appear, they do not do so for extended periods.
6
Q
occurs months or years after radiation exposure
A
late tissue reactions
7
Q
is a “science that deals with the incidence, distribution, and control of disease in a population.” (Travis, 1989)
A
Epidemiology
8
Q
studies consist of observations and statistical analysis of data, such as the incidence of disease within groups of people.
A
Epidemiology
9
Q
The incident rates at which these irradiation-related malignancies occur are determined by comparing the natural incidence of cancer occurring in a human population with the prevalence of cancer occurring in an irradiated population.
A
Epidemiology
10
Q
The later studies include the risk of radiation-induced cancer.
A
Epidemiology
11
Q
Risk factors are then identified for the general human population
A
Epidemiology
12
Q
studies are of significant value to radiobiologists who use the information from these studies to formulate dose–response estimates for predicting the risk of cancer in human populations exposed to low doses of ionizing radiation.
A
Epidemiologic
13
Q
also called tumorigenesis, is the formation of a cancer
A
Carcinogenesis
14
Q
Carcinogenesis, also called
A
tumorigenesis
15
Q
is the most significant late stochastic effect caused by exposure to ionizing radiation
A
Cancer
16
Q
Cancer is the name used for a substantial group of diseases in which healthy cells have been transformed into nonstandard cells that divide uncontrollably. The process leads to an expansive growth of abnormal structures within various locations in the body and the destruction of surrounding body tissues such as bone marrow. The altered or cancer cells readily demonstrate the potential to invade or spread to other parts of the body.
A
Carcinogenesis
17
Q
is demonstrated graphically through a curve (the dose–response [DR] curve) that maps the observed effects of radiation exposure in relation to the dose of radiation received.
A
radiation dose–response relationship
18
Q
Information obtained can be used to attempt to predict the risk of occurrence of malignancies in human populations that have been exposed to low levels of ionizing radiation
A
radiation dose–response relationship
19
Q
The “effect” in question may be the incidence of a disease (e.g., cases of cancer per million in a population or fatalities due to cancer per million in a population), or the effect may be its degree of acuteness, such as the severity of cataracts as dose increases.
- The observed effects of radiation exposure may be the incidence of a disease, or it may be the severity of an effect
A
radiation dose–response relationship
20
Q
The DR curve is either linear (straight line) or nonlinear (curved to some degree), and it depicts either a threshold dose or a nonthreshold dose
A
radiation dose–response relationship
21
Q
straight line
A
linear
22
Q
curved to some degree
A
nonlinear
23
Q
medical term for eyes
A
cataracts
24
Q
blood
A
leukemia
25
offspring
genetic mutations
25
cancer is
random
25
long term effects use what kind of dose
low doses of radiation
26
short term effects use
high doses of radiation
26
increase radiation
increase biological damage
27
anything below .1 sievert
cannot be measured
28
anything above .1 sievert
can be measured
29
is defined as a point or level at which a response or reaction to an increasing stimulation first occurs
threshold
29
means up to a certain point there's no biological response. after it passes point there is
threshold
30
this means that below a certain absorbed radiation dose, no biologic effects are observed
threshold
31
The biologic effects begin to occur only when what kind of dose is reached
threshold
32
no dose is a safe dose
non threshold
33
indicates that a radiation absorbed dose of any magnitude has the capability of producing a biologic effect
non threshold
34
No radiation dose can be considered absolutely safe with the severity of the biologic effects increasing directly with the magnitude of the absoradiation not a direct effect
nonthreshold
35
how does linear effect radiation
direct effect to radiaton
36
how does non linear effect radiation
not a direct effect
37
biologic effect responses will be caused by ionizing radiation in living organisms in a directly proportional manner at any dose above zero
linear nonthreshold
38
biologic effect responses will be caused by ionizing radiation in living organisms in a directly proportional manner all the way down to dose levels approaching zero
linear nonthreshold
39
proclaims that no radiation dose can be considered absolutely “safe,” with the incidence of the biologic effects increasing directly with the magnitude of the absorbed dose.
a linear nonthreshold (LNT) relationship.
40
what is the radiation doubling equivalent dose for humans?
1.56 Sv
41
is the radiation dose that causes the number of spontaneous mutations occurring in a given generation to increase to two times their original number
doubling dose
42
what is the most important late effect
cancer
43
below how many sieverts cannot be measured
0.1
44
is long term low or high doses
low doses
45
is short term high or low doses
higher doses
46
implies that the equation that best fits the data has components that depend on dose to the first power (linear or straight-line behavior) and also on dose squared (quadratic or curved behavior).
linear-quadratic
47
recommends the use of the linear nonthreshold curve of radiation dose–response (LNT DR) for most types
of cancers
48
if the absorbed dose is doubled, the biologic response probability, and therefore its actual occurrence in a large population sample, is also doubled
linear nonthreshold curve (LNT DR)
48
quadratic means
unknown is over estimated
49
what graph does diagnostic radiology follow
linear-quadratic nonthreshold
50
This curve displays a more conservative dose–response outcome for low-level radiation
linear-quadratic nonthreshold dose ( LQNT DR)
51
relationship to be an improved reflection of stochastic and genetic effects at low-dose levels from low-LET radiation
linear-quadratic nonthreshold dose ( LQNT DR)
52
implies that the biologic response to ionizing radiation is directly proportional to the dose received
Linear nonthreshold (LNT)
53
what does a tail in a graph mean
recovery or death
54
what means random or unknown
stochastic
55
what does radation protection fall under in regards to radiation dose- response
linear non threshold
56
The curve estimates the risk associated with low-dose levels from low LET radiation
Linear quadratic nonthreshold
57
what committee believes that the linear-quadratic nonthreshold curve (LQNT) is a more accurate reflection of stochastic somatic and genetic effects at low-dose levels from low-LET radiation.
BEIR committee
58
to be an improved reflection of stochastic and genetic effects at low-dose levels from low-LET radiation
Linear quadratic nonthreshold ( LQNT)
59
What curve does leukemia , breast cancer, and heritable damage follow
Linear quadratic nonthreshold ( LQNT)
59
what does leukemia follow
LQNT
60
what does breast cancer follow
LQNT
61
what does heritable damage follow
LQNT
61
long term effect follow what kind of radiation
low let radiation
62
short term effects follow what kind of radiation
high LET radiation
63
This depicts those cases for which a biologic response does not occur below a specific radiation dose
linear threshold
64
what curve represents skin erythema and hematologic depression
linear threshold
65
what curve does skin erythema follow
linear threshold
66
what curve does hematologic depression follow
linear threshold
67
Laboratory experiments on animals and data from human populations observed after high doses of radiation provided the foundation for this curve
linear threshold dose–response curve (LT DR)
68
is generally employed in radiation therapy to demonstrate the high-dose cellular response to the radiation absorbed doses within specific tissues, such as skin, the lens of the eye, and various types of blood cells.
sigmoid, or S-shaped (nonlinear), threshold curve
68
Sigmoid or S shaped
nonlinear
68
indicates that limited recovery occurs at lower radiation doses
tail of the curve
69
the curve gradually levels off and then veers downward because the affected living specimen or tissue dies before the observable effect appears
at the highest radiation doses
(tail)
70
what curve does radiation therapy use
nonlinear threshold
70
The continued use of the linear dose–response model for radiation protection standards has the potential to exaggerate the seriousness of radiation effects at lower dose levels from low-LET radiation. Regulatory agencies such as the Nuclear Regulatory Commission continue to review scientific literature to determine if the evidence supports changes in the use of this model for setting radiation protection standards. In establishing such standards, the regulatory agencies have chosen to be conservative—that is, to use a model that may overestimate risk at low doses but is not expected to underestimate risk.
The rationale for risk model selection
71
When living organisms that have been exposed to radiation sustain biologic damage, the effects of this exposure are classified as
Somatic effects
72
somatic effects, from the Greek sōmatikos, meaning
“of the body.”
73
The classification of somatic effects may be subdivided into:
- stochastic effects
- tissue reactions
74
the probability that the effect occurs depends upon the received dose, but the severity of the effect does not
stochastic effects
75
random / unknown
- is it going to happen or not
example: occurrence of cancer
stochastic effects
76
both the probability and the severity of the effect depend upon the dose.
tissue reactions (deterministic)
77
is going to happen
- increase dose increase severity
example: a cataract
tissue reactions
78
is an effect in the offspring of the individual who was irradiated.
A non-somatic effect
78
An example of a non-somatic effect is
the irradiation of an individual’s genetic material (sperm or eggs) leading to a genetic malformation in offspring
79
are consequences of radiation exposure that appear months or years afterwards
Late somatic effects
79
Late effects may be either
stochastic or tissue reactions
80
such as the incidence of cancers in a population, typically are not noticeable for many years in the exposed population.
Stochastic effects
81
such as skin effects, may be perceptible sooner in individuals, although months or years may pass before their full expression.
Tissue reactions
82
are the result of slowly developing changes to body tissues that may be modified by other factors, such as medical intervention, after the exposure.
Tissue reactions
83
such as the occurrence of cancer, are generally determined at the time of irradiation.
Stochastic effects
84
examples of late tissue reactions
- Cataract formation
- Fibrosis
- Organ atrophy
- Loss of parenchymal cells
- Reduced fertility
- Sterility
85
examples of Teratogenic effects
(i.e., effects of radiation on the embryo-fetus in utero that depend on the fetal stage of development and the radiation dose received)
- Embryonic, fetal, or neonatal death
- Congenital malformations
- Decreased birth weight
- Disturbances in growth and/or development
- Increased stillbirths
- Infant mortality
- Childhood malignancy
- Childhood mortality
86
examples of stochastic effects
Cancer
Genetic (hereditary) effects
87
late somatic effects may result from
Previous whole- or partial-body acute exposure
Previous high radiation doses
Long-term low-level doses sustained over several years
88
Absolutely going to happen
Absolute risk
89
looking at the probability
relative risk
90
effects happening to fetus
teratogenic effects
91
effects of radiation on the embryo -fetus in utero that depend on the fetal stage of development and the radiation dose recieved
teratogenic effects
91
examples of Teratogenic Effects
-embryonic, fetal, neonatal death
-congenital malformations
-decreased birth weight
-disturbance in growth and or development
-increased stillbirths
-infant mortality
-childhood malignancy
-childhood mortality
92
Using all data available on high radiation exposure, members of the scientific and medical communities determined that three categories of adverse health consequences require study at low-levels of exposur
Cancer induction
Damage to the unborn from irradiation in utero
Genetic (hereditary) effect
93
Low-level doses are a consideration for patients and personnel exposed to ionizing radiation as a result of diagnostic imaging procedures.
The risk estimate for humans contracting cancer from low-level radiation exposure is still controversial.
No conclusive proof exists that low-level ionizing radiation exposure below 0.1 Gy causes a significant increase in the risk of malignancy.
Risk may be negligible or even nonexistent
Risk Estimate for Contracting Cancer fromLow-Level Radiation Exposure
94
Sources of such low-level radiation include the following:
* X-rays and radioactive materials used for diagnostic purposes
* Employment-related exposures in medicine and industry
* Natural background exposure
95
Cells that survive the initial irradiation may have incurred some form of damage.
Theoretically, radiation damage to just one or a few cells of an individual could actually produce a stochastic effect such as a malignancy or a hereditary disorder many years after radiation exposure.
Tissue reactions such as skin reactions do not usually demonstrate a late onset.
Extreme reactions associated with high skin doses may persist for some time, but will usually occur in weeks or months after the exposure
late effects
( Low-level effects)
96
Tissue reactions such as skin reactions do not usually demonstrate a late onset you only see it when
when you can only see it in the beginning
97
cells can either
- survive
- be damage
- have cell death
98
the three major types of late effects are:
* Carcinogenesis
* Cataractogenesis
* Embryologic effects (birth defects)
99
Carcinogenesis is considered a
stochastic event random which is your cancer
100
Cataractogenesis is considered a
late tissue reactions is known you are going to get it
101
Embryologic effects (birth defects) is considered a
stochastic events random not known if it will happen or not
102
Exposure to ionizing radiation may cause cancer as a
stochastic effect
103
At low equivalent doses, below 0.1 Sv, which includes groups such as occupationally exposed individuals and virtually all patients in diagnostic radiology, this risk is not directly measurable in population studies.
Reasons::
*The risk is overshadowed by other causes of cancer in humans.
*The risk is zero
104
at high doses how is the risk measurable
At high doses, the risk is measurable in exposed human populations
105
:Utilizes the linear nonthreshold dose–response relationship and assumes that risk still exists
May be determined by extrapolating from high-dose data, in which the risk has been directly observed, down to the low doses, in which it has not been observed (a controversial concept)
Current radiation protection philosophy
106
-May be given in terms of absolute risk or relative risk caused by a specific exposure to ionizing radiation (over and above background exposure)
-Both models predict the number of excess cancers, or cancers that would not have occurred in the population in question without the exposure to ionizing radiation
Risk Estimates To Predict Cancer Incidence
107
This model forecasts that a specific number of malignancies will occur as a result of exposure. definitely going to happen
absolute risk
108
model predicts that the number of excess cancers will increase as the natural incidence of cancer increases with advancing age in a population. in the sense that this model predicts a percentage increase in incidence rather than a specific number of cases.
- a probability type of a model
- increase radiation dose increase probability of biological damage
relative risk
109
suggest that although the radiation doses received by patients in diagnostic radiology imaging could be considered in determining the risk of cancer, the benefit to the patient of the information gained from an imaging procedure greatly exceeds the minimal theoretical risk to the patient for developing cancer as a late stochastic response to diagnostic radiation exposure.
Epidemiologic Studies for Determining the Risk of Cancer
110
Researchers commonly use two models for extrapolation of risk from high-dose to low-dose data,
Linear
Linear-quadratic
111
-supported the linear-quadratic model for leukemia only
- For all other cancers recommended adoption of the linear model to fit the available data.
BEIR V Committee
112
is the most important late stochastic effect caused by exposure to ionizing radiation
cancer
113
This reaction is a random occurrence that does not seem to have a threshold and for which the severity of the disease is not dose-related
Carcinogenesis (Cancer)
114
Laboratory experiments with animals and statistical studies of human populations exposed to ionizing radiation prove that radiation induces:
cancer
115
a patient’s leukemia induced by a low-dose exposure is no different from a person’s leukemia that was caused by a high-dose exposure)
true or false
true
115
cancer is
random and unknown
116
may take 5 or more years to develop in humans
radiation induced cancer
117
true or false:
Cancer caused by low-level radiation is difficult to identify
true
118
true or false
The physical appearance of cancer induced by ionizing radiation does not appear different than a cancer caused by other agents.
true
119
first radiation induce cancer happened when
1902
120
Human evidence of radiation carcinogenesis comes from
epidemiologic studies conducted many years after subjects were exposed to high doses of ionizing radiation
121
which cancer is more common
Cancer from natural causes family cancer
122
Incidence of leukemia has slowly declined since the late 1940s and early 1950s.Occurrence rates of other radiation-induced malignancies have continued to escalate since the late 1950s and early 1960s.Includes a variety of solid tumors such as thyroid, breast, lung, and bone cancers
Incidence of Leukemia Rate of Other Radiation-Induced Malignancies
123
leukemia will have its peak at
5 years and then slowly down to zero
124
every other type of cancer will peak at
at 10 years and then down to 30 and 40
125
Hence radiation-induced leukemia is assumed to follow
an linear nonthreshold
126
The 1986 nuclear power station accident at Chernobyl requires long-term follow-up studies to assess the magnitude and severity of late effects on the exposed population. Detailed observations investigating potential increases in the
incidence of leukemia, thyroid problems, breast cancer, and other possible radiation-induced malignancies will continue.
127
Radiation was then believed to have accelerated all causes of death. This reduction in the life cycle is known as
nonspecific life span shortening
128
true or false
Incidence of leukemia has slowly declined since the late 1940s and early 1950s
true
129
what type of cancer would develop after five years and then dwindle off
leukemia
130
this type of cancer is the same low vs high dose
leukemia
130
what cancer would you see after ten years and then it would peak down the road
any other cancer other than leukemia
130
The probability that a single dose of ionizing radiation of approximately 2 Gyt will induce the formation of
cataracts (Cataractogenesis)
131
at what dose will you get cataracts
2 Gy
132
what is the threshold for cataracts to form
0.5 gy
133
what curve does cataracts follow
non linear threshold
134
what is the most sensitive part of the eye when it comes to radiation
the lens
135
The lens of the eye contains
transparent fibers that transmit light
136
result of cataractogenesis
Partial or complete loss of vision
Results of laboratory experiments with mice
Radiation-induced cataracts in humans follow a threshold, nonlinear dose–response relationship
136
Evidence of human radiation cataractogenesis originates from
the observation of small groups of people who accidentally received substantial doses to the eyes
137
Gestation in humans is divided into three stages or periods:
1. Preimplantation
2. Organogenesis,
3. The fetal stage
138
0-9 days
-if you received 0.05-0.15 gy there will be death of the baby
preimplantation
139
what is the preimplantation stage
which corresponds to 0 to 9 days after conception
140
how much dose recieved will cause death of the baby in preimplantation
the range of 0.05 to 0.15 Gyt,
141
what is the organogenesis stage
which lasts approximately from 10 days postconception to 12 weeks after conception
142
which is the most susceptible stage of gestation
- most sensitive least resistant
organogenesis
(because its the first trimester)
142
Abnormalities may include:
* skeletal damage
* Growth inhibition
* Intellectual disability
* Microcephaly
* Genital deformities
* Sensory organ damage
organogenesis
143
what is the fetal stage
which extends from the 12th week to term
144
true or false
the further you are along in pregnancy, the more mature the baby is
true
145
Fetal radiosensitivity decreases
as gestation progresses
146
during the second and third trimesters of pregnancy when lesser numbers of cells are differentiating, the developing fetus is
less susceptible to ionizing radiation exposure
147
most sensitive part in trimester
first trimester
148
stem cells are
immature and very sensitive
149
first trimester most sensitive then
third trimester
150
Biologic consequences of ionizing radiation on future generations are termed
genetic or hereditary effects
151
They can occur as a result of radiation-induced damage to the DNA molecule in the sperm or ova of an adult, leading to germ cell alterations, which cause incorrect genetic information to be transmitted to the offspring.
irradiated mutations
152
Cause of genetic mutations:
Radiation-induced damage to the DNA molecule in the sperm or ova of an adult
Natural spontaneous mutations
Resultant genetic disorders or diseases
153
what percentage of all births have some sort of hereditary disorder
10%
153
what level does genetic mutations happen
molecular level
153
radiation dose required to double the genetic diseases
doubling dose
154
what curve is cataracts
nonlinear threshold and nonstochastic
154
what curve is thyroid
Linear nonthreshold and stochastic
154
what curve is breast cancer
Linear non threshold and stochastic
155
what curve is bone marrow
linear threshold
156
what curve is skin
Non stochastic(deterministic) and threshold
157
in men, what dose causes permanent sterility
5-6 gy
157
what curve is stochastic
Follows nonthreshold
157
what curve is deterministic
follow a threshold
-tissue reactions
158
who holds and who doesnt
students dont hold
-occupational radiological workers don’t hold
-male before female in child bearing age
159
who should hold:
-65 yo radiologist
-40 yo male tech
-25 yo student tech
-21 female nurse
the 21 yo female nurse
160
who should hold
-60 yo male tech
-42 yo baby mama
-21 yo baby daddy
58 yo gma
-the 58 yo gma
161
what curve is skin erythema
Linear Threshold
162
what curve is hemotologic depression
linear threshold
163
what curve is cataractogenesis
linear threshold
164
what curve is radiation protection
linear non threshold
165
what curve is radiation therapy
nonlinear threshold
165
what curve is teratogenic
nonlinear threshold
166
what curve is diagnostic xray
LQNT
167
what curve is leukemia
LQNT
168
what curve is breast cancer
LQNT
168
what curve is heretiable damge
LQNT
169
Some modifications in genetic material occur naturally, without a known cause. They are referred to as
- These can be transmitted from one generation to the next and may cause a wide variety of disorders or diseases,
spontaneous mutations
169
increase radiation dose increase biological damage
increase chance of mutations
170
a dominant gene is
a gene pass to the offspring
171
what is a recessive gene
a gene pass on to it future generations
171
Point mutations (genetic mutations at the molecular level) may be either
dominant (probably expressed in the offspring) or recessive (perhaps not expressed for several generations).
172
Radiation is thought to cause primarily
recessive mutations
172
Radiation-induced hereditary effects in humans have not been demonstrated
persons employed in diagnostic imaging or in patients undergoing radiologic examinations
173
is, by definition, the radiation dose that causes the number of spontaneous mutations occurring in a given generation to increase to two times their original occurrence
doubling dose
174
the radiation doubling dose for humans, as determined from studies of the children of the atomic bomb survivors of Hiroshima and Nagasaki, is estimated to have a mean value of
1.56 Sv
175
A linear nonthreshold (LNT) curve is currently used for most types of
cancers
175
Risk of leukemia, breast cancer, and genetic effects associated with low-level radiation is typically estimated with the
linear-quadratic nonthreshold (LQNT) curve
175
Late tissue reactions may be demonstrated graphically through the use of
a linear threshold (LT) curve of radiation dose–response.
176
High-dose cellular response may be demonstrated through the use of a
(nonlinear) sigmoid threshold curve.
176
Late effects include:
- carcinogenesis,
- cataractogenesis,
- embryologic (birth) defects.
176
Effects thaestimates that a specific number of malignancies will occur as a result of radiation exposure.t have no threshold, that occur arbitrarily, that have a severity that does not depend on dose, and that occur months or years after exposure are called
stochastic effects
177
is the most significant stochastic somatic effect caused by exposure to ionizing radiation.
cancer
177
estimates that a specific number of malignancies will occur as a result of radiation exposure
The absolute risk model
178
predicts that the number of excess cancers rises as the natural incidence of cancer increases with advancing age in a population.
The relative risk model
179
are used for extrapolation of risk from high-dose to low-dose data.
Linear and linear-quadratic models
180
Radiation-induced congenital abnormalities can occur approximately
from 10 days to 12 weeks after conception
180
is the most critical period for radiation exposure of the embryo-fetus.
The first trimester of pregnancy
181
skeletal abnormalities most frequently occur from
weeks 3 to 20
181
Radiation exposure even in the second and third trimesters can potentially cause:
- congenital abnormalities,
- functional disorders,
- predisposition to the development of childhood cancer
181
measures the effectiveness of ionizing radiation in causing mutations; it is the radiation dose that causes the number of spontaneous mutations in a given generation to increase to two times their original occurrence.
Doubling dose
182
For humans, the doubling dose is estimated to have a mean value of
1.56 Sv.
182
lens of the eye in sievert
150 sv
183
all other organs in sievert
500 sv
184
- killing the cells with high doses of radiation
- threshold
- appears above a given threshold
deterministic
185
- severity does not depend on dose
- nonthreshold
- random in nature
- found in low dose radiation
- cancer, genetic effects
stochastic effects
186
- random, unpredictable, probablistic
- probability of an effect occuring increases with exposure
- severity of an effect is not affected by the dose
- no relationship between dose and severity
- nonthreshold
- cancer, genetic effects
- linear nonthreshold model
stochastic
187
- predictable
- effects occur at specific dose thresholds
- examples; cataracts, epilation, skin erythema, decreased sperm counts
- threshold model
deterministic
188
states that NO level of radiation can be considered completely safe and the degree of response is directly proportional to the amount of radiation received
Linear-non threshold relationship
189
States that a dose of radiation exists below which a response does not occur; when that threshold is crossed, the response is directly proportional to the dose received(i.e. cataractogenesis does not occur at low levels of radiation exposure; therefore there is a threshold, or a safe dose.
Linear-threshold relationship
190
states that a safe (threshold) dose of radiation exists, when exceeded, results in responses that are not directly proportional to the dose received.
Nonlinear-threshold relationship
191
States that no level of radiation can be considered safe and the degree of the response is not directly proportional to the dose received.
Nonlinear-non threshold relationship
191
Randomly occurring effects of radiation; the probability of such effects is proportional to the dose ( increased dose equals increased probability, not severity, of effects.)
Stochastic effects
191
Effects that become more severe at high levels of radiation exposure and do not occur below a certain threshold dose.
deterministic (non stochastic)
192
means random in nature – probability of occurrence of effects, rather than severity, increase with dose (leukemia at 1 Gy is same at 1 cG
stochastic
193
thought to be nonthreshold – damage to multiple or single cell can cause risk (linear and linear quadratic) – even small exposures can carry risk – risk proportional to dose with no threshold
stochastic
194
– radiation induced cancer, radiation induced genetic effects
Stochastic effect
195
are main health risk from low dose radiation in diagnostic
stochastic effects
195
– thought to be threshold
– there are always doses below which the effect is not observed (cataracts, erythema, fibrosis, hemopoetic damage)
- relevant to serious radiation accidents
– not likely during diagnostic or occupational exposure
-Increase in severity with dose
Nonstochastic (deterministic)
196
point at which a response or reaction to an increasing stimulation first occurs
-Below a certain radiation dose, no biological effects are observed
threshold
197
any radiation dose has the capability of producing a biologic effect. No radiation dose is safe, exhibits some effect no matter how small
nonthreshold
198
biological response to radiation is directly proportional to dose received, straight line when graphed
linear
198
No fixed proportional response between dose and response, form a curved line when graphed
nonlinear
199
Factors that affect dose mode
– time period over which radiation is delivered, age, state of health, time between exposures
200
Early effects result from high radiation doses – they are all
– most frequent is skin injury higher the dose, faster the onset of symptoms
deterministic
201
What examples fall under Linear Nonthreshold (LNT) curve?
- stochastic
- cancer
- radiation protection
- thyroid
- breast tissue
202
What examples fall under Linear Threshold (LT) curve?
- skin erythemaa
- hematologic depression
- bone marrow
203
What examples fall under Nonlinear Threshold (NLT) curve?
- caractogenesis
- radiation therapy
- teratogenic effects
204
What examples fall under Linear Quadratic Nonthreshold (LQNT) curve?
- diagnostic x-ray
- leukemia
- breast cancer
- heritable damage
