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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.

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Chapter 37 Late Effects of Radiation

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  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

  6. 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.

  7. 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.

  8. 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.

  9. Radiodermitis

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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).

  15. 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.

  16. 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.

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

  18. 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 Risk of Life Shortening as a Consequence of Disease or Occupation

  19. 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

  20. 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.

  21. 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 inthe irradiated group • The relative risk for radiation induced late effects is between 1 and 2.

  22. 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.

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

  24. 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.

  25. 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.

  26. 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.

  27. 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

  28. 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.

  29. 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.

  30. Leukemia • The relative risk from the study was 10:1. • The threshold with a 95% confidence was 300 rad.

  31. 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.

  32. 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.

  33. 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.

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

  35. 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.

  36. 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.

  37. 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

  38. 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.

  39. 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.

  40. 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.

  41. 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.

  42. 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 BEIR Committee estimates for mortality from malignancy in 100.000 people

  43. 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 id absolute or relative.

  44. Exposure at an Early Age • The age response was a slight bulge of cancer after the latent period.

  45. 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.

  46. 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.

  47. 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 Average Annual Risk of Death from Various Causes

  48. End of Lecture

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