chapter 9 EXAM 4 Flashcards
late effects
radiation induced damage at the cellular level that may lead to somatic and genetic damage in the living organism later in life
epidemiology definition
science that deals with the incidence, distribution, and control of disease in a population
dose response curves establish relationships between
radiation and dose response
radiation dose response relationship
graph that maps out the effects of radiation observed in relation to the dose of radiation received
horizontal axis of dose response curve =
dose received
vertical axis of dose response curve =
biologic effects observed
the curve on the dose response curve can be either
linear or non linear
the curve on a dose response curve can depict
threshold dose or non threshold dose
threshold relationship
a point at which a response or reaction to an increasing stimulation occurs
below a certain radiation level or dose, no biologic effects are observed
nonthreshold relationship
means that any radiation dose will produce a biologic effect
no dose is believed to be “safe”
what is the BEIR committee
committee on the Biologic Effects of Ionizing Radiation (BEIR)
the BEIR committee report of 1980 stated
the majority of stochastic somatic effects at low dose levels appear to follow a linear quadratic nonthreshold curve (LQNT)
the BEIR committee report of 1990 stated
the risk of radiation exposure was about 3-4 times greater than previously projected
currently BEIR committee recommends the use of what for most types of cancer
the linear nonthreshold curve
linear nonthreshold curve (LNT) implies
that the chance of a biologic response to ionizing radiation is directly proportional to the dose received
The LNT curve accurately reflects the effects of
high LET radiation at higher doses
deterministic (nonstochastic) effects of significant radiation may be demonstrated graphically through the use of a
linear threshold curve
the sigmoid or s-shaped (nonlinear) threshold curve is generally used in
radiation therapy to demonstrate high dose cellular response to radiation within specific tissues
somatic effects
biologic effects that occur in the living organism that have been exposed to radiation
non somatic effects
irradiation of an individuals genetic material leading to genetic malformation
called genetic/heritable effects
somatic effects may be subdivided into
- stochastic effects
2. deterministic effects (nonstochastic effects)
stochastic effects
non threshold
mutational or randomly occurring biologic changes independent of dose
ex: cancer
deterministic (nonstochastic) effects
effects directly related to the dose received
cell killing effects that exhibit a threshold dose
non-random
ex: cataracts
late somatic effects
consequences of radiation exposure that appear months or years after exposure
late deterministic somatic effects are directly related to
the dose received
late stochastic effects
do not have a threshold and occur in random and have a severity that is not dose dependent
low level radiation is defined as
an absorbed dose of 0.1 Sv (10rem) or less delivered over a short period of time
a typical routine chest xray is about what dose
0.06 Sv (6mrem)
3 major types of late effects
- carcinogenesis
- cataractogenesis
- embryonologic effects
absolute risk model predicts
that a specific number of excess cancers will occur as a result of exposure
relative risk model predicts
that the number of excess cancers will increase as the natural incidence of cancer increases with advancing age
predicts a percentage increase rather than a specific number of cases
what is the most important late stochastic somatic effect caused by exposure to ionizing radiation
cancer
radium watch-dial painters
1920-1930 pointed their radium containing brush tips with their lips and spit this caused osteoporosis osteogenic carcinoma other malignancies
uranium miners
they mined uranium and sustained lethal doses of radiation caused by breathing dust and drinking radioactive water
died from cancer and respiratory diseases
early medical radiation workers
exposed to large amounts of radiation
developed cancerous skin lesions
higher incidence of aplastic anemia and lukemia
pts. injected with contrast agent thorotrast
1925-1945 radioactive material emitted alpha particles and were deposited in pts. causing liver and spleen cancer angiosarcoma biliary duct carcinomas
infants treated for enlarged thymus gland
1940-50s infants were treated with therapeutic doses to reduce size of thymus gland
resulted in development 20 yrs later of thyroid nodules and carcinoma
children of the marshall islanders
children on neighboring islands received substantial absorbed doses to thyroid from external and internal exposures
ethos projects
research project in aftermath of chernobyl
nonspecific life span shortening
the reduction in life cycle due to radiation
the probability that a single dose of radiation about 2 Gy (200rad) will induce formation of cataracts is
high
neutron dose of what has been known to cause cataracts in mice
a neutron dose of 0.01 (1 rad)
radiation induced cataracts in humans follow a
threshold nonlinear dose response relationship
3 stages of gestation in humans
- preimplantation
- organogenesis
- fetal stage
irradiation of embryo dureing the first 12 weeks of development to EqD in excess of 200 mSV (200rem) frequently results in
death or causes congenital abnormalities
when a high dose of radiation is received witihin aprox. 2 weeks of fertilization, what happens
prenatal death and usually results in spontaneous abortion
if this does not happen pregnancy will continue with no adverse effect
if during the preimplantation stage you are irradiated with a dose in the range of what, what will occur
in a dose of 0.05-0.15 Gyt
embryonic death will occur
during oganogenesis if you are irradiated,
fetus is more susceptible to abnormalities such as growth inhibition, mental retardation, microcephaly, genital deformities etc.
if radiation occurs during late stages of organogensis,
the presence of abnormalities in the fetus will cause neonatal death
the United Nations Scientific Committee on Effects of Atomic Radiation proposed an upper limit combined radiation risk for these fetal effects to be
3 chances per 1000 children for reach rem of fetal dose (0.3%)
international chernobyl project
study compared seven contaminated russian villages with 6 uncontaminated villages
spontaneous mutations
a natural phenomenon involving alterations in genes and DNA
occur at random and without a known cause
are permanent and heritable and can be transmitted from 1 generation to the next
cause a wide variety of disorders/diseases
mutagens
agents that increase the frequency of occurrence of mutations
agents of mutagens include
elevated temps.
ionizing radiation
viruses
absorption of certain chemicals
what is one of the more effective mutagen
ionizing radiation
because mutant genes cannot properly run cell’s normal chemical reactions, it results in
various genetic diseases
point mutations
genetic mutations in which the chomosome is not broken but the DNA within it is damaged
may be either dominant or recessive
dominant point mutations
expressed in offspring
recessive point mutations
not expressed for several generations
radiation is thought to cause what mutations
primarily recessive mutations
in order for recessive mutation to appear in offspring, both parents must have
have the same genetic defect, therefore it is not likely to appear in a population
damage from recessive mutations may sometimes manifest itself more subtly and may appear as
allergies
slight alteration in metabolism
decreased intelligence
predisposition to certain diseases
doubling dose is
the radiation dose that causes the number of spontaneous mutations occurring in a given generation to increase to two times their original number
for humans the doubling dose is estimated to have a mean value of
1.56 Sv (156 rem)
measurable delayed biologic damage are
Cataracts
Leukemia
Genetic mutations
