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