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Module 4 Biological Effects of Ionizing Radiation

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Presentation on theme: "Module 4 Biological Effects of Ionizing Radiation"— Presentation transcript:

1 Module 4 Biological Effects of Ionizing Radiation

2 Terminology Acute vs. Chronic Exposure Direct vs. Indirect Action
Prompt vs. Delayed Effects Stochastic vs. Non-stochastic Effects An understanding of what Health Physicists mean when we use a particular term will help in discussing radiation and its effects in this class and as you read about and discuss these issues in the future. A.First lets look at the differences between acute and chronic exposure.1.An acute exposure means an exposure that is received over a short time, perhaps as long as a few days.2.A chronic exposure is one that is received continuously (or repeatedly) over a long period of time. Most occupational exposures fall into this category.B.Next consider prompt vs. delayed effects.1.Prompt effects are those that appear within a few days of exposure.2.Delayed effects are those that appear several years after the exposure.3.We’ll look at some examples of both cases later.C.We’ll discuss Direct vs. Indirect action and Stochastic and Non-stochastic effects in detail. Module #4

3 Chain of Events for Direct Action
Incident particle or photon Excitation or Ionization Dissociation of a molecule due to the excitation or ionization on one of the molecules atoms Biological Effects possible depending on the molecule dissociated Module #4

4 Direct Action A break in the DNA molecule due to direct action of the radiation or an electron that is freed from an atom Module #4

5 Chain of Events for Indirect Action
1. Incident Particle or Photon Ionization of Water Molecule Dissociation of Water Molecule Free Radicals Produced Chemical Changes Possible Biological Effects Module #4

6 Indirect Action H2O  H2O+ + e- H2O+  H+ + OH H2O + e -  H2O-
Radiation ionizes a water molecule The positive ion dissociates The electron attaches to a neutral water molecule The negative ion then dissociates Module #4

7 Indirect Action (cont.)
H + H H2 OH + OH  H2O2 H + O2 HO2 HO2 + H  H2O2 The H radicals combine to form hydrogen gas Hydrogen peroxide is produce through two mechanisms Module #4

8 Stochastic (Random) Effects
Occur by chance Occur in both exposed and unexposed individuals Are not unequivocally related to the radiation exposure Become more likely as dose increases Severity is independent of the dose Module #4

9 Linear No Threshold Model
Assumes that any amount of radiation has a detrimental effect Is not a predictive model Is used to establish regulatory dose limits (NRC) 1 Probability of Occurrence 0.5 Dose Module #4

10 Examples Cancer Mental Retardation Genetic Effects Module #4

11 Cancer Radiation induced tumors most frequent in the hemopoietic system, thyroid, and skin. Cancer induction is well documented at doses of 100 rad or more Induction at lower doses is inconclusive (possible exceptions are leukemia and thyroid cancer) Tumor induction has a latent time of 5-20 years Module #4

12 Cancer (cont.) Radiation induced leukemia in Atomic bomb survivors has been documented at doses above 40 rad Bone Cancer induction has been documented in laboratory animals for large injection of “bone seeking” radionuclide Radiation induced lung cancer is seen mainly in underground miners exposed to high Radon concentrations Module #4

13 Mental Retardation Most pronounced in those exposed between the 8th and 17th week of pregnancy Brain cells divide rapidly during this period Has been observed in children exposed in-utero to radiation from the atomic bombs in Japan Module #4

14 Genetic Effects No radiation induced genetic effects have been observed in humans Genetic effects have been observed in animal studies Module #4

15 Non-stochastic (Deterministic) Effects
A certain minimum dose must be exceeded before the effect occurs The severity of the effect increases as dose increase There is a clear causal relationship between exposure and occurrence Module #4

16 Nonlinear Threshold Response
No response is seen until the threshold dose is exceeded At some dose all individual experience the effect Applies to non-stochastic effects 100 Present Response 50 Dose Module #4

17 Non-stochastic Effects
Sterility Cataracts Skin Erythema Hemopoietic Syndrome Gastrointestinal (GI) Syndrome Central Nervous System Syndrome Module #4

18 Sterility Temporary sterility had been observed
In men at doses as low as 30 rads In women at doses as low as 300 rads The higher the dose the longer the period of sterility Module #4

19 Cataracts Cataracts Threshold eye dose of about 200 rads of beta or gamma radiation Threshold may be as low as 60 rads for neutron radiation Long latent period Module #4

20 Erythema & Other Skin Effects
Reddening of the skin (erythema) occurs at photon or beta doses of about 300 rads Higher does may cause epilation, blistering, necrosis, and ulceration Module #4

21 Hemopoietic Syndrome Blood changes may be seen at doses as low as 14 rads Blood changes almost certain at doses above 50 rads Module #4

22 Hemopoietic Syndrome Hemopoietic Syndrome appears at about 200 rads
Characterized by depression or ablation of the bone marrow May be accompanied by nausea, vomiting, fatigue, and increased temperature Death occurs within 1-2 months unless medical treatment is successful Module #4

23 Gastrointestinal Syndrome
Occurs at a whole body dose of 1000 rads or greater Characterized by the destruction of the intestinal epithelium and complete destruction of the bone marrow Accompanied by severe nausea, vomiting, and diarrhea soon after exposure Death occurs within a few weeks Module #4

24 Central Nervous System Syndrome
Occurs at whole body doses of 2000 rads or more Damages the central nervous system as well as all other organs and systems Unconsciousness occurs within minutes Death follows in a matter of a few hours to a few days Module #4

25 Summary Biological effects of concern in the occupational setting do not appear until several years after radiation exposure if they appear at all The probability of these effects increases with dose In any individual case it can never be determine with 100% confidence that radiation was the cause Module #4

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