Week 9 a Chapter 37 Late effects of Radiation Exposure

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Week 9a Chapter 37 Late
Effects of Radiation
Chapter 37 Late Effects of
Radiation
• The early effects of radiation exposure are
produced by high radiation doses.
• The radiation exposure from diagnostic
radiology are low level and of low LET.
• They are chronic in nature because they
are delivered intermittently and over a long
period of time.
• Therefore the late effects of exposure are
of great importance.
Late Effects of Radiation
• Radiation exposure experienced by
working in diagnostic radiology are low
dose and low linear energy transfer (LET).
• Diagnostic imaging exposures are
delivered intermittently over long periods.
• The principle late effects are radiation
induced malignancy and genetic effects.
Late Effects of Radiation
• Radiation protection guideline are based upon
the late effects of radiation and on linear,
nonthreshold dose response relationships.
• Most late effects are known as stochastic
effects.
– The response is of an increasing incidents and not
severity response to increased exposure.
– There is no threshold for a stochastic response.
Epidemiologic Studies
• Studies of large numbers of people
exposed to toxic substances require
considerable statistical analysis.
• Epidemiologic studies of people exposed
to radiation are difficult because
– The actual exposure dose is usually not
known.
– The frequency of response is low.
Epidemiologic Studies
• The results of radiation epidemiologic
studies do not carry the statistical
accuracy that observations of early effects
do.
Local Tissue Effects
• Skin
– In addition to the early effects of erythema and
desquamation and late-developing carcinoma,
chronic irradiation of the skin can result in severe
nonmalignant changes.
– Early radiologists who did fluoroscopy without
protective gloves developed very callused, discolored
and weathered appearance to the skin of the hands
and forearm. It would sometimes become brittle and
severely crack or flake.
– It was called radiodermatitis. The dose necessary to
produce the effect was very high and not observed in
current practice.
Local Tissue Effects
• Chromosomes
– Irradiation of the blood forming organs can
produce hematologic depression as an early
response and leukemia as a late response.
– Chromosome damage of the circulating
lymphocytes can produce early and late
response.
Local Tissue Effects
• Chromosomes
– The type and frequency of aberrations have
been discussed earlier, however, even a low
dose of radiation can produce chromosome
aberrations that may not be apparent for
many years after the exposure.
– Individuals accidentally exposed with high
radiation doses continue to show
chromosome abnormalities for 20 years after
the exposure.
Local Tissue Effects
• Chromosomes
– The late effects may be due to radiation
damage to the lymphocyte stem cells. These
cells may not be stimulated into replication
and maturation for many years.
• Cataracts
– Cyclotrons used to accelerate charged
particle to very high energies were developed
in 1932.
Local Tissue Effects
• Cataracts
– Cyclotrons used to accelerate charged particle to very
high energies were developed in 1932.
– By 1940 nearly every university physics department
had one and was engaged in high energy
experiments.
– The early cyclotrons were in one room and a beam of
high energy were extracted through a tube and
steered to the target material in an adjacent room.
– The physicists used a fluoroscopic screen to aid in
locating the beam.
Local Tissue Effects
• Cataracts
– This resulted in the physicist looking directly
into the beam and received high doses of
radiation to the lens of the eyes.
– First cataracts reported in 1949 and by 1960’s
several hundred cases were reported.
– Radiation induced cataracts occur in the
posterior pole of the lens.
Local Tissue Effects
• Cataracts
– Through observations several conclusions
were drawn about radiation induced cataracts.
• Radiosensitivity of the eyes is age dependent.
– The older the individual
– The greater the radiation effect
– The shorter latent period range from 5 to 30 years.
Average is 15 years.
– High LET radiation have high RBE for the production of
cataracts
Local Tissue Effects
• Cataracts
• The dose response relationship for
cataracts is nonlinear, threshold response.
• At 1000 rad ( 10GyT) cataracts develop in
about 100% of individuals irradiated.
• The threshold after an acute x-ray
exposure is about 200 rad (2 GyT)
• The threshold after fractionated exposure
is probably in excess of 1000 rad (10GyT).
Local Tissue Effects
• Cataracts
• Occupational exposures are too low to
require protective lens. It is nearly
impossible for medical radiation workers to
reach the threshold.
• Radiation administered to patients during
head or neck examinations using
fluoroscopy or CT can be significant.
Life Span Shortening
• There have been
animal experiments
conducted for both
acute and chronic
exposure that show
that irradiated animals
die young.
• The dose response is
linear non threshold.
Life Span Shortening
• As noted earlier,
American radiologist
had a shorter life
span in the early 20th
century.
• The difference has
disappeared since
1960.
Risk of Life Shortening as a Consequence of
Disease or Occupation
•
•
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•
•
Risky Condition
Male
Heart disease
Single
Smoke a pack a day
Coal Miner
Cancer
30 pounds overweight
All accidents
Motor vehicle accidents
Occupational Accidents
Radiation worker
Airplane crashes
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•
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•
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Expected Days of Life Lost
2800 days
2100 days
2000 days
1600 days
1100 days
980 days
900 days
435 days
200 days
74 days
12 days
1 day
Life Span Shortening
• At the worst case, humans can expect a
reduced life span of about 10 days per
rad.
• Performing radiography is a safe
occupation
Risk estimates
• The early effects of high dose radiation exposure
are easy to observe and measure.
• The late effects are also easy to observe but
nearly impossible to associate a particular late
response with a previous exposure.
• Consequently dose-response relationships are
often not possible to formulate so we must resort
to risk estimates.
Relative risk estimates
• Relative risk = Observed cases
Expected cases
• A relative risk of 1 is no risk
• A relative risk of 1.5 means that late response to
exposure is 50% higher in the irradiated group
• The relative risk for radiation induced late effects
is between 1 and 2.
Excess Risk
• Excess risk= Observed cases – Expected
cases.
• Leukemia is know to occur in nonirradiated populations.
• If the number of cases in a irradiated
population is higher, the difference is the
excess risk.
Absolute Risk
• If at least two dose
levels of exposure are
known, then it may be
possible to determine
an absolute risk.
Radiation Induced Malignancy
• Many of the dose response conclusions
for humans are based upon animal
research
• Human studies have been based upon
data on radiation accident victims, atom
bomb survivors, Radiologist, radiation
therapy patient and children irradiated in
utero to name a few.
Radiation Induced Malignancy
• The greatest wealth of information is on
atom bomb survivors. At the time of the
bombing about 300,000 people lived in
those two cities.
– Nearly 100,000 died from the blast and early
effects.
– Another 100,000 received a high dose but
survived.
– The remainder received less than 10 rad.
Radiation Induced Malignancy
• The Atomic Bomb Casualty Commission
(ABCC) attempted to determine the
radiation dose received by each survivor
but factoring distance from the explosion,
terrain, type of bomb and type of building if
the survivor was inside.
• The survivors who received high doses
had 100 times more incident of leukemia.
Leukemia
• Radiation induced
leukemia follows a
linear, non threshold
dose response
relationship.
• Radiation induced
leukemia is
considered to have a
latent period of 4 to 7
years and an at risk
period of 20 years
Leukemia
• Studies on data from early American
radiologist showed an alarmingly high
incidence of leukemia. They served as a
radiologist and radiation oncologist without
the benefit of modern radiation protection.
• Most radiologist received doses exceeding
100 rad/year.
• There is no evidence of radiation induced
leukemia in radiologic technologists.
Leukemia
• In the 1940’s & 1950’s in Great Britain,
patients with ankylosing spondylitis were
treated with radiation to cure the disease.
• It remained to treatment of choice for over
20 years until patients cured started dying
from leukemia.
• The spinal bone marrow had received
exposures from 100 to 4000 rad.
Leukemia
• The relative risk from the study was 10:1.
• The threshold with a 95% confidence was
300 rad.
Cancer
• What we have seen for leukemia and also be
seen for cancer. There is not as much data on
cancer but it can be said that radiation can
cause cancer.
• The relative and absolute risks are shown to be
similar to leukemia. Several types of cancer
have been implicated as radiation induced.
• It is not possible to link any case of cancer to a
previous radiation exposure. About 20% of
deaths are from cancer so radiation induced
cancers are obscured.
Thyroid Cancer
• Thyroid cancer has developed in three
groups of patients whose thyroid was
irradiated in childhood.
– The first two groups were treated shortly after
birth for enlarged thymus with up to 500 rad.
The thymus shrank and no problem were
noted until 20 years later when thyroid
nodules and cancers developed in some
patients.
Thyroid Cancer
– The other group was 21 children natives of
the Rongelap Atoll in 1954. During hydrogen
bomb tests, the winds shifted carrying fall out
to their island. They received both external
and internal exposure of about 1200 rad.
Thyroid Cancer
• The number of
cancers and
preneoplastic nodules
were shown to have a
linear, non-threshold
dose response.
Bone Cancer
• Two groups have contributed to the
knowledge of radiation induced bone
cancers.
– Radium watch dial painters.
– Patients treated with radium for arthritis and
tuberculosis.
Radium Watch Dial Painters
– In the 1920’s & 1930’s workers sat a benches and
painted radium sulfate on watch dials to make them
luminous.
– Radium salts emit alpha and beta particles exciting
the luminous compound to make the dial glow in the
dark.
– It was fine detail work so the often touched the paint
brushes to their tongue. Radium was ingested.
– Radium is metabolized like calcium and deposited in
the bone. Radium has a half life of 1620 years so the
bone received up to 50,000 rad.
Radium Watch Dial Painters
• 72 bone cancers in about 800 workers
have been observed in 50 years of
observation.
• The relative risk was 122:1
Skin Cancer
• Skin cancers usually begins with the
development of radiodermitis.
• Significant data is available on patients treated
with orthovoltage (200 to 300 kVp) and
superficial x-rays (50 to 150 kVp).
• The latent period is about 5 to 10 years.
• The relative risk for exposure range of 500 to
2000 rad the relative risk was 4:1.
• For exposure of 4000 rad to 6000 rad the
relative risk is 14:1.
Total Risk of Malignancy
• The overall absolute risk for induction of
malignancy is approximately 8/10,000 rad
with the at risk period of 20 to 25 years.
• Lethality of radiation induced malignancy
is 50%.
• 400 deaths from radiation induced
malignancy can be expected after an
exposure of 1 rad to 10,000 persons.
Three-Mile Island
• There was an incident at the three mile island
nuclear power plant in 1979. About 2,000,000
people lived within 50 miles from the plant. This
population received about 8 mrad exposure.
• Normally there would be 330,000 of cancer
deaths in this population. One could expect not
more than one added death from the radiation.
• At twice that exposure, there would only be 1.2
added deaths.
BEIR Committee
• In 1990, the Committee on Biologic Effects
of Ionizing Radiation (BEIR) reviewed data
on late effects of low-LET radiation.
• They studied three situations.
– A one time accidental exposure to 10 rad:
highly unlikely in diagnostic radiology.
– One rad per year for life: possible for medical
radiologist but unlikely.
– 100 mrad/year continuous exposure.
BEIR Committee estimates for mortality from
malignancy in 100.000 people
• Normal expectations
• Excess cases
• Single 10 rad exposure
• Continuous exposure to 1
rad/year
• Continuous exposure to
100 mrad/year
• Male
• 20,460
Female
16,680
• 770
• 2880
810
3070
• 520
600
BEIR Report
• The committee stated that because of the
uncertainty in their analysis, less than 1
rad/year may not be harmful.
• They also looks at available data with
regard to the age at exposure with a
limited time of expression of effects to
determine if the response is absolute or
relative.
Exposure at an Early Age
• The age response
was a slight bulge of
cancer after the latent
period.
Relative Risk Model
• The relative risk
model show how the
excess radiation
induced cancers is
proportional to the
natural incidents.
• This is the most
recognized model.
Absolute Risk Model
• The absolute risk
model predicts that
the excess radiation
induced cancers is
constant for life.
• The best way to
compare risks is a
comparison to other
known risks.
Average Annual Risk of Death from
Various Causes
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Cause
All causes
Smoker pack a day
Heart Disease
Cancer
25 years old
Auto accident
Radiation 100 mrad
Texas Gulf hurricane
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Change of death this year
1 in 100
1 in 280
1 in 300
1 in 520
1 in 700
1 in 4000
1 in 100,000
1 in 4,500,000
End of Lecture
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