Lecture 9 dosimeters

• Radiation can not be measured directly.
• Posting and Warning signs are necessary for sources and distribution of average radiation exposure to the world’s population.
• Always operate the equipment from behind the protective barrier or using lead equivalent apron.
• The technologist is responsible for protecting the patient, protecting himself, using safe exposure factors, and avoiding repeating exposures.
• Radiation Exposure is defined as the number of ions created in air by radiation.
• Exposure or "Exposure dose" is the quantity of the ionization in the air due to ionizing radiation from photons, which reveal the amount of radiation traveling through the air.
• The SI unit for exposure is coulomb/kg of air.
• 1 Roentgen (R) = 2.58 × 10^-2 C/Kg or (0.000258 C/Kg).
• Ionization is what happens when radiation photons separate an electrons from atoms.
• If a radiation source (like X-ray tube) produces a radiation exposure of 1 C/kg, that means the radiation source produces 6242 × 10^-2 ions/kg.
• 1 C/kg and 1 R are very large exposure values.
• In medical imaging, it is much more common to see radiation exposure in Milli-Roentgen (mR) or Micro-coulomb (µC/kg).
• The quantity of photons is expressed by an air-kerma.
• Air kerma is the energy transferred to electrons in a given mass of air (energy/mass).
• Air kerma can be thought of as the number of x-rays per unit area.
• Radiation in Air - Air KERMA is the quantity that expresses the concentration of radiation energy absorbed at a specific point within the body tissue.
• Radiation from medical examinations is similar to sunlight.
• The effect of sunlight on the skin depends on the light's intensity, how long a person stays in it, and the sensitivity of the skin.
• The total dose to the worker and the public from any radiation source should be within the dose limits as specified in Principles of Radiation Protection.
• Collimation to the area of interest reduces scatter radiation.
• Thermo-luminescent Dosimeter (TLD) is a small device used to measure the radiation dose by measuring the amount of light emitted from a crystal in the detector when the crystal is heated after being exposed to the radiation.
• Less time spent near the X-ray source results in less radiation exposure.
• Personal Dosimetry includes TLDs and OSLs.
• Providing a protective apron to the attendant while holding patients is a radiation safety measure.
• Radiation Safety involves minimizing radiation exposure by using time, distance, shielding, and operation safety principles.
• Shielding with barriers of lead, concrete, or very dense material provides protection from penetrating radiation.
• More distance from the X-ray source results in less radiation exposure.
• Radiation dose limits for staff working with radiation and for the members of the public are specified in Principles of Radiation Protection.
• For alpha particles, W R is 20.
• The Inverse Square Law states that doubling distance from the source decreases dose by a factor of four.
• While there are no specified dose limits for patients, there is a responsibility to ensure that all exposures are justified and optimized as per Principles of Radiation Protection.
• Optically Simulated Luminescent Dosimeters (OSL) are similar to TLDs except that the light emission is stimulated by a laser light instead of heat.
• ALARA stands for As Low As Reasonably Achievable, which means avoiding exposure to radiation that does not have a direct benefit to you, even if the dose is small.
• An active dosimeter produces a radiation-induced signal and displays a direct reading of the detected dose or dose rate in real time.
• LET is expressed in the units of kiloelectron volts of energy transferred per micrometer in tissue (keV µm).
• An ionization chamber is used to determine the exact activity of radioactive dose.
• A dosimeter is a device that measures exposure, air kerma, absorbed dose, and equivalent dose.
• A Giger counter is used to detect many radiation in the background α- and β- particles.
• High LET radiation can deposit most of its energy within the volume of one cell of the body and the chance of damage to the cell DNA is therefore larger.
• A personal dosimeter is a small radiation detection device worn by an individual, used to measure doses from ionizing radiation.