Basic radiation protection & radiobiology By Dr. Mohsen Dashti Patient care & management 202 Wednesday, October 13, 2010
Ionizing radiation. Discussion issues 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.
Manmade radiation. Ionizing radiation - What happens to x-rays when they are produced? 1. Absorbed. 2. Scatter. 3. Pass through undistributed.
Manmade radiation. Ionizing 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.
Radiation risk. Ionizing radiation
ALARA Ionizing radiation - 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.
2. Distance: Protecting the patient - 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.
3. Shielding: Protecting the patient - 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