Basic radiation protection & radiobiology

By

Dr. Mohsen DashtiPatient care & management 202

14-3-10

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 patient2. 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 patient3. 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 patient3. 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

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