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
•   Risky Condition           •   Expected Days of Life Lost
•   Male                      •   2800 days
•   Heart disease             •   2100 days
•   Single                    •   2000 days
•   Smoke a pack a day        •   1600 days
•   Coal Miner                •   1100 days
•   Cancer                    •   980 days
•   30 pounds overweight      •   900 days
•   All accidents             •   435 days
•   Motor vehicle accidents   •   200 days
•   Occupational Accidents    •   74 days
•   Radiation worker          •   12 days
•   Airplane crashes          •   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 non-
  irradiated 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

                             • Male     Female
• Normal expectations        • 20,460   16,680
• Excess cases
• Single 10 rad exposure     • 770      810
• Continuous exposure to 1   • 2880     3070
  rad/year
• Continuous exposure to     • 520      600
  100 mrad/year
             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
•   Cause                  •   Change of death this year
•   All causes             •   1 in 100
•   Smoker pack a day      •   1 in 280
•   Heart Disease          •   1 in 300
•   Cancer                 •   1 in 520
•   25 years old           •   1 in 700
•   Auto accident          •   1 in 4000
•   Radiation 100 mrad     •   1 in 100,000
•   Texas Gulf hurricane   •   1 in 4,500,000
     End of Lecture

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posted:8/3/2011
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