BIOLOGICAL EFFECTS OF RADIATION

1. Mrs. BHUVANESHWARI.P
M.Sc. MEDICAL PHYSICS
LECTURER
GANGA COLLEGE OF NURSING
COIMBATORE

2. BIOLOGICAL EFFECTS OF
RADIATION

3. Radiation
What is it?
Energy Being Transmitted Through Space
• Electromagnetic (x rays, gamma
photons)
• Particulate (alpha particles, beta
particles, electrons, neutrons)

4. Sources of Radiation
• Sources of radiation can be divided into two
categories:
–Natural Background Radiation
–Man-Made Radiation
• Radiation is part of nature. All living
creatures, from the beginning of time, have
been, and are still being, exposed to radiation.

5. Natural Background Radiation
• Cosmic Radiation
• Terrestrial Radiation
• Internal Radiation

6. Cosmic Radiation
• The earth, and all living things on it, are
constantly bombarded by radiation from outer
space.
• Charged particles from the sun and stars
interact with the earth’s atmosphere and
magnetic field to produce a shower of
radiation.

7. Terrestrial Radiation
• Radioactive elements are found in soil, water,
and vegetation.
• Important radioactive elements include
uranium and thorium and their radioactive
decay products which have been present
since the earth was formed billions of years
ago.
• Some radioactive material is ingested with
food and water. Radon gas, a radioactive
decay product of uranium is inhaled.

8. Internal Radiation
• People are exposed to radiation from
radioactive material inside their bodies.
Besides radon, the most important internal
radioactive element is naturally occurring
potassium-40 but uranium and thorium are
also present.
• On average, in the United States radon
contributes 55% or all radiation exposure
from natural and man-made sources.
Another 11% comes from the other
radioactive materials inside the body.

9. Man-Made Radiation
Machines
• Medicine –
• diagnostic (x ray, fluoroscopes, CAT
scans)
• therapeutic (accelerators)
• Industry and Research (x ray,
accelerators)

10. Man-Made Radiation
Radioactive Material
• Medicine –
• diagnostic (thyroid scans, stress tests)
• therapeutic (cobalt irradiation [cancer],
hyperthyroid treatment)
• Biological and Medical Research (tracers, radio-
pharmaceuticals, drug development)
• Industry - (thickness/density gauges, well
logging)

11. Man-Made Radiation
Radioactive Material (continued)
• Industry - Electric generation (nuclear power
plants)
• Consumer products - Luminous dials, fire
detectors, exit lights, dishware
• Defense - Nuclear weapons, nuclear powered
naval vessels, security devices

12. Calculate Your Own
Background Radiation Dose
• Background calculator from Los Alamos
National Laboratory

13. Background Radiation

14. Regulation of Exposure
• The Nuclear Regulatory Commission and
other federal and state agencies regulate
exposure from man-made radiation sources.
Different regulations apply to two distinct
groups:
–Members of the public
–Occupational workers

15. Absorbed Dose
• The energy absorbed in a material per
unit mass of the material.
• SI unit: gray (Gy)
• Traditional unit: rad (1 Gy = 100 rad)

16. Relative Biological Effectiveness
• RBE
– Ratio of the absorbed dose from a
standard radiation (250 kVp x rays) to
produce a given biological effect to the
absorbed dose from a radiation of interest
to produce the same effect.

17. Relative Biological Effectiveness

18. Quality Factor
• Quality factor (Q)
Consensus value of RBEs for a
particular type of radiation. Examples:
radiation Q
betas and electrons 1
x rays and gammas 1
protons and neutrons 10
alphas 20

19. Dose Equivalent
• Dose equivalent (H): allows the
description of the biological effect of an
absorbed dose.
H = DQ
• SI unit: sievert (Sv)
• Traditional unit: rem 1 Sv = 100 rem

20. Sequence to Biological Effect
• Physical: less than seconds
• Chemical: seconds
• Biological: seconds to many years
– Reactions with molecules, cells
– Tissue changes
– Cancer, leukemia

21. Physical
• Interactions of radiation with matter
• Direct ionization of atomic electrons by
charged particles
• Indirect indirect ionization by neutral
particles

22. Chemical
• Chemical alteration of biological
molecules
• Direct effect: molecule receives energy
directly from incident radiation
producing ions and free radicals
• Indirect effect: molecule altered by
interaction with ions or free radicals

23. Biological
• Law of Bergonie and Tribondeau
The radiosensitivity of a population of
cells is directly proportional to their
mitotic rate and inversely proportional to
their degree of differentiation.

24. Biological Outcomes
• The radiation may enter the body but
miss important targets.
• The radiation may not cause any
damage to a target.
• The damage may be repaired.
• A damaged cell may die.
• A damaged cell may be changed
(mutated).

25. Biological – Acute Effects
• Acute effects: acute radiation syndrome
at high doses
• Hematopoietic syndrome
• Gastrointestinal syndrome
• Cardiovascular and central nervous
system syndrome

26. Biological – Delayed Effects
• Somatic, genetic and teratogenic effects
–cancer and leukemia
–inherited effects
–effects to embryo and fetus
• Stochastic and non-stochastic biological
effects

27. U.S. Regulatory Limits
• Radiation worker:
– 5 rem/yr = 50 mSv/yr
• Individual member of the general public:
– 0.1 rem/yr = 1 mSv/yr
• Compare to
– average background: 0.36 rem/yr = 3.6
mSv/yr
– LD50/30: 450 rad = 4.50 Gy

28. Basis for Regulatory Limits
• Sources of information on biological
effects
• Lack of information (or effect) at low
doses
• Dose response models

29. Sources of Information
• Animal experiments
• Accidental massive irradiation
• Hiroshima-Nagasaki survivors
• Occupational exposures
• Patients
• Nuclear weapons tests participants
• Chernobyl

30. Dose Response Models
• Data on cancer induction is from high
radiation exposures (100 rad and higher).
• No evidence of genetic effects in humans.
• Must extrapolate high level data to low
exposures.
• Model used in regulations:
Linear, no threshold

31. Dose Response Models

32. Low Dose Facts
• Radiogenic health effects in humans are
observed only at doses in excess of 5-10 rem
delivered at high dose rates.
• Below 5-10 rem, estimation of adverse health
effects is speculative since risks of health effects
are either too small to be observed or are non-
existent.
• Epidemiological studies have not demonstrated
adverse health effects in individuals exposed to
less than 10 rem delivered over long time periods.

33. Low Doses: What we don’t know
• Are there any bad effects below about
5-10 rem?
• Are there beneficial effects below about
5-10 rem?
• Are any there inherited effects at any
dose?

34. References
• Federal Regulation: Title 10: Energy
Chapter I: Nuclear Regulatory Commission
Part 20: Standards for Protection Against
Radiation
• Radiation and Health Physics Page
• Health Physics Society

35. THANK YOU