Basic Considerations of
Radiation Safety and Barrier Protection

Safety Principles The medical profession has taken many steps to protect patients and medical personnel from the risks of radiation. There are three fundamental principles of radiation protection: Minimal time of exposure - Minimizing the duration of exposure directly reduces radiation dose. Simply put, if the amount of time spent near a radiation source is reduced, the amount of radiation exposure received will also decrease. A common analogy: if you spend a lot of time at the beach, you will be exposed to the sun and ultimately get sunburn. If you spend less time in the sun and more time in the shade, your sunburn will be much less severe. This is similar to the way radiation exposure works. Maximum distance from the radiation beam - When the working distance from a radiation source is increased by a factor of two, the dose received from that source will be reduced by a factor of four. Therefore, a person or object 40 feet from a radiation source will receive 1/4 of the exposure than that of a person 20 feet from the source. Compare this to an outdoor concert, and think of the radiation as the music emanating from the speakers. A person sitting directly in front of the speaker may suffer some permanent hearing damage. A person 50 yards from the stage will most likely be exposed to music of average intensity. And a person in a park across the street may not even hear the concert. Radiation exposure is similar: the closer you are to the source, the greater your chances are for damaging your body. Use of all possible shielding - Shielding is the use of any material to reduce the intensity of the radiation by absorption or reflection. Increasing the shielding around a radiation source decreases the exposure. Example: if you stand in the rain without an umbrella, you will get wet. But, if you use an umbrella as a shield, you will remain dry and protected. Also, think of complete coverage and optimum protection by incorporating boots, raincoat, hat, and a larger umbrella. This is similar to radiation shielding in which the specific shielding material and thickness depends on the amount and type of radiation involved. Employing Plexiglas for beta particles and lead for x-rays and gamma rays is an effective way to reduce radiation exposure. Shielding is gauged by the amount of protection that reduces exposure from a radiation source by one-half. This is termed the half-value layer (HVL), which is dependent on both the energy of the radiation and the atomic number of the absorbing material. While this exact terminology may not be of clinical relevance, it is important because it is part of the lexicon that describes the interaction of x-rays with shielding materials. ALARA is an acronym for As Low As Reasonably Achievable. This is a radiation safety principle for minimizing radiation doses by employing all reasonable methods. ALARA is a regulatory requirement for all radiation safety programs. It is the core of any radiation protection program and a mindset of professional excellence. One can never have "zero" radiation exposure due to naturally occurring radioactivity that surrounds us - cosmic rays, the sun, natural isotopes in our body, etc. Therefore, it is best to add nothing to this background dose. The ALARA approach used by the U.S. Nuclear Regulatory Commission (NRC) assumes that any exposure to ionizing radiation carries some risk. The risk is assumed to be linear, so as one's exposure increases, so does the risk of adverse health effects. Instead of operating at or just below permissible exposure limits, one must stay as far below the exposure limits as possible. This affords a wider margin of safety, because should a control malfunction or fail, one's exposure level may rise yet still remain below the acceptable level.

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