Chapter 37 Late Effects of Radiation

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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.

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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.

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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.

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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.

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Epidemiologic Studies

• The results of radiation epidemiologic studies
  do not carry the statistical accuracy that
  observations of early effects do.

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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 an 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 no
  observed in current practice.

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Radiodermitis
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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.

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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.

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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.

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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.

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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 1960s
  several hundred cases were reported.
• Radiation induced cataracts occur in the
  posterior pole of the lens.

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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

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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).

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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.

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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.

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Life Span Shortening

• As noted earlier, American radiologist had a
  shorter life span in the early 20th century.
• The difference has disappeared since 1960.

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Risk of Life Shortening as a Consequence of
Disease or Occupation

• 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

• 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

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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

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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.

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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.

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Excess Risk

• Excess risk Observed cases Expected cases.
• Leukemia is known to occur in non-irradiated
  populations.
• If the number of cases in a irradiated population
  is higher, the difference is the excess risk.

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Absolute Risk

• If at least two dose levels of exposure are
  known, then it may be possible to determine an
  absolute risk.

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Radiation Induced Malignancy

• Many of the dose response conclusions for humans
  are based upon animal research
• Human studies have been bases upon data on
  radiation accident victims, atom bomb survivors,
  Radiologist, radiation therapy patient and
  children irradiated in utero to name a few.

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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.

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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.

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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

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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.

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Leukemia

• In the 1940s 1950s 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.

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Leukemia

• The relative risk from the study was 101.
• The threshold with a 95 confidence was 300 rad.

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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.

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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.

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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.

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Thyroid Cancer

• The number of cancers and preneoplastic nodules
  were shown to have a linear, non-threshold dose
  response.

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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.

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Radium Watch Dial Painters

• In the 1920s 1930s 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.

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Radium Watch Dial Painters

• 72 bone cancers in about 800 workers have been
  observed in 50 years of observation.
• The relative risk was 1221

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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 41.
• For exposure of 4000 rad to 6000 rad the relative
  risk is 141.

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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.

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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.

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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.

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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 Female
• 20,460 16,680
• 770 810
• 2880 3070
• 520 600

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BEIR Report

• The committee stated that because of the
  uncertainty in their analysis, less than 1
  rad/year may not be harmful.
• They also looked 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.

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Exposure at an Early Age

• The age response was a slight bulge of cancer
  after the latent period.

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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.

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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.

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Average Annual Risk of Death from Various Causes

• Cause
• All causes
• Smoker pack a day
• Heart Disease
• Cancer
• 25 years old
• Auto accident
• Radiation 100 mrad
• Texas Gulf hurricane

• 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

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Approach to Statistics

• The risks to patients from irradiation is very
  low but they are real.
• The odds of winning the lotto or being struck by
  lightning are also low but every year, someone
  wins or is struck.
• As professional users of radiation, we owe the
  patients and ourselves safe operation and
  protection practices.

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End of Lecture