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Basic radiation protection &
radiobiology
By
Dr. Mohsen Dashti
Patient care & management 202Wednesday, October 13, 2010
Discussion issues
• Ionizing radiation.
• Protecting the patient.
• Protecting the radiographer.
• Radiation monitoring.
Ionizing radiation
• What are the sources of ionizing radiation?
1. Natural radiation.
- What is natural radiation?
-- Sources of radiation that occur spontaneously in
nature and can be affected by human activity.
- Examples:
-- Cosmic radiation….. The sun and other planets.
-- Radioactive substances on earth…. Uranium and
radium.
- Natural radiation sources are given less attention to
their hazardous potential.
Ionizing radiation
• What are the sources of ionizing radiation?2. Manmade radiation.
- What is manmade radiation?
-- Sources of radiation that are developed by humans and used in different fields of technology.
- Examples:
-- Nuclear industry…. Weapons & nuclear power stations.
-- Radionuclide…. Radioactive elements & radiopharmaceuticals.
-- Medical radiation…. Medical imaging & dental exposure.
Ionizing radiation• Manmade radiation.
- It is known as x-rays, which is a form of
electromagnetic radiation that travels at the speed of
light depositing energy randomly.
• How can we produce x-rays?
1. Source of electrons.
2. Force to move electrons rapidly.
3. Element to stop this movement rapidly.
Ionizing radiation
• Manmade radiation.
- What happens to x-rays when they are produced?
1. Absorbed.
2. Scatter.
3. Pass through undistributed.
Ionizing radiation
• Manmade radiation.
- How do x-rays interact with matter?
1. Classic coherent scattering.
-- Interaction with matter in which a low-energy photon
(below 10 keV) is absorbed and released with its same
energy, frequency and wavelength but with change of
direction.
2. Photoelectric interaction.
-- Interaction with matter in which proton strikes an
inner shell electron, causing its ejection from orbit with
complete absorption of the photon’s energy.
Ionizing radiation• Manmade radiation.- How do x-rays interact with matter?
3. Compton scattering.
-- Interaction with matter in which a higher-energy photon strikes a loosely bound outer electron, removing it from its shell, and the remaining energy is released as scatter photon.
4. Pair production.
-- Interaction between matter and photon possessing a minimum of 1.02 MeV of energy, producing two oppositely charged particles.
5. Photodisintegration.
-- Interaction directly with the nucleus of photon possessing a minimum of 10 MeV, causing excitement followed by emission of nuclear fragment.
Ionizing Radiation
• Standards for regulation of exposure:
- What guidelines available to limit radiation dose?
1. No-threshold.
-- No dose exists below which the risk of damage does
not exist.
2. Risk versus benefit.
-- The benefit to the patient performing radiographic
procedure far outweigh the risk of possible biologic
damage.
Ionizing radiation
• Radiation risk.
Ionizing radiation
• ALARA…
- To keep radiation dose as low as reasonably
achievable.
-- The annual whole-body dose-equivalent limit for the
occupational worker is 50mSv (5 rem).
-- The whole-body dose-equivalent limit for the general
population is one tenth the occupational worker’s annual
limit or 5 msv (0.5 rem).
- Sv: unit in the SI system to measure the dose-equivalent
or biologic effectiveness of differing radiation; 1 Sv is
equal to 100 rems.
Ionizing radiation
Protecting the patient
• ALARA concept can be practiced with the
patient by utilizing 3 methods:
1. Time:
- Time minimization is the most important element to
protect the patient from radiation dose. How?
-- Applying the rules of radiographic techniques.
-- Using the exposure chart to determine the correct
amount of radiation to produce an image.
-- Minimizing repeat rates to reduce the patient’s time
in the path of the x-ray beam.
Protecting the patient
2. Distance:
- Distance maximization is another element to reduce
patient radiation dose. Why?
-- This serve to lessens the skin or entrance dose to
the patient.
-- Increasing the distance should be kept to a
reasonable range so radiation dose will not be
affected. How?
-- For you to answer???
3. Shielding:
- Use of shield to protect sensitive or unexposed region
of the patient’s body is another method to protect the
patient from radiation dose.
Protecting the patient
3. Shielding:
- The rule indicates that patients should be shielded
whenever they are 4-5 cm from the primary x-ray
beam.
-- Shields are made of lead, which absorbs x-rays
through the process of photoelectric effect, thereby
minimizing patient exposure.
• Types of shield:
1. Flat contact shield: made of a combination of vinyl and
lead. Placed directly over the gonads of the patient.
2. Shaped shield: cup shaped and made specifically for
male patients.
Protecting the patient
3. Shadow shield: mounted on the side of the collimator
of the x-ray tube and can be manipulated to extend
into the path of the beam.
Protecting the radiographer
• The same methods are used to protect the
radiographer from extra radiation dose.
- The radiographer should spend the least amount of time
possible in a room when a source of radiation is active.
- Fluoroscopy requires the radiographer to spend longer
time in an active radiation room, therefore extra
protection should be considered.
- Distance is the best measure to protect the radiographer
from radiation dose.
- Inverse square law should be applied to reduce the
impact of radiation dose.
Protecting the radiographer
• Inverse square law: The intensity of radiation varies
inversely with the square of the distance. What does it
mean?
-- For you to answer???
- Submit your answer next
week 20-10-10
Protecting the patient
- Lead shield and aprons must be used by the
radiographer whenever radiation is active.
- Aprons and lead shields must in in good conditions and
crack free to avoid passing radiation into the
radiographer.
- The minimum permissible amount of lead equivalency
for aprons used where the peak kilovoltage is 100 should
be 0.25 mm.
Radiation monitoring
- Discuss the four main radiation
monitoring methods used in x-
rays: film badges,
thermoluminescent dosimeters,
pocket dosimeters, and field
survey instruments.
See you next week