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Radiation_Protection_in_Medical_Imaging_(Part 4)

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Radiation protection is built into any room designated for use with radiation equipment. Two types of barriers, primary and secondary, coincide with protection from either the primary beam or secondary scatter. The primary beam is the photon energy directed from the X-ray tube, through a patient, to an image receptor. The primary beam is given the most consideration because it contains the highest amount of radiation. Any wall, including ceilings and floors, perpendicular to the path of the X-ray beam, must have at least an equivalent filtration of 1/16 inch of lead. This is considered a primary barrier. Secondary barriers are used to protect technologists and other personal from scattered radiation coming from the tube, the beam or the patient. Secondary barriers could be half that of a primary barrier or the equivalent of a 1/32 inches of lead. Both primary and secondary barriers can be constructed of any material as long as the thickness used provides the needed protection. Several factors are considered when engineers decide how much protection is built into a particular room. The workload factor relates to how often the room is used for radiation work and general kilovolt levels used. The occupancy factor refers to the use of rooms adjacent to the radiation work space who is using them such as radiation workers, non-radiation workers, or the public and the possibility of exposure. The calculations for these and recommended construction information are included in reports 49 and 102 from the NCRP. Radiologic technologists don't have to think about inherent protection because it is a built in safety feature in all radiology departments. However, technologists can take steps to further protect themselves from primary and secondary radiation. One method of protection is a mobile shield, which is a vertical piece of plexiglas or metal on wheels. It can be positioned so that a technologist or other personal can step behind it during a fluoroscopic procedure or radiographic exposure when a lead apron isn't available or practical. These devices should contain between 0.5 millimeter and 1 millimeter of lead equivalent to absorb scatter radiation sufficiently. Mobile shields are particularly useful in the operating room when one diagnostic image is being taken but they aren't very practical for use for the CR. The term lead shield can be misleading because shields are no longer made of lead but instead use a lighter weight composite of other metals such as tungsten or tin at a thickness that's equivalent to the properties of lead. Lead shields come in different shapes and sizes to protect certain body parts. The most frequently used apron is the body apron which must be at least a lead equivalent to 0.25 millimeters. The apron is used to protect the bulk of the chest area down through the gonads on the anterior sides. Aprons generally have velcro straps that are used to secure the sides but some have wraparound straps that place less stress on the shoulders and back. Because aprons only protect a wearer from the front, a technologist should never turn his or her back to the primary beam or the patient who may emit scatter. This same lead equivalent applies to vest and skirt shielding which can be used during fluoroscopy. This pairing provides full protection from the chest to the gonads for the front, back and to the sides. Compared to the apron alone, the extra protection of the vest skirt combination increases the weight of shielding and might be a consideration for the technologists. Because of the one size fits all approach, lead aprons and vests may fit loosely and generally don't fully protect the thyroid, which is a butterfly shaped gland that sits above the sternal notch in this area. This gland is sensitive to radiation and should be shielded, whenever possible, with a thyroid shield of 0.5 millimeter lead equivalent or greater. A thyroid shield is fairly lightweight, wraps around the neck and secures the back with velcro. Although the radiologic technologists should avoid intercepting the primary beam if possible, sometimes it's unavoidable especially during fluoroscopy. During upper GI exams, for example, a technologist may need to help patients turn over or hand them barium to drink during the test. In these cases, a technologist should wear lead lined gloves to protect his or her hands and wrists. These gloves must have at least a 0.25 millimeter lead equivalent. Additionally, protective eyewear should be worn during lengthy fluoroscopic procedures. Slightly heavier than regular glasses, protective eyeglasses should have side panels of leaded glass and must have 0.5 millimeter of lead equivalent. Technologist can reduce their exposure to 1/4 of the original dose by doubling their distance from the source. For example, if a technologist stands one foot from a source of radiation where the intensity is 10 mR, and then moves back another foot from the source, universe square law tell us that the intensity of radiation will be reduced to 1/4 its original reading. So doubling your distance from a radiation source will reduce your exposure to 1/4, or in this case, 2.5 mR. Time, shielding and distance are cardinal rules of radiation protection. Understandably, limiting exposure time helps minimize dose and shielding protects the technologists from low dose scatter radiation. However, maintaining distance from the source of the scatter is the easiest way for technologists to protect themselves. During their initial education, radiologic technologists are taught that time, distance and shielding are the best ways to protect themselves from radiation exposure and adhere to the ALARA principle. If technologists spend as little time as possible near radiation, stand as far as possible from the source, and use their shielding, their occupational dose should stay relatively low. However, special consideration should be taken into account depending upon the modality. Modern radiography departments may use computed radiography, digital radiography, film cassettes or a combination of all three. Regardless of how the image is captured, the radiation used for any type of radiography is the same. Although the chosen imaging method may affect patient dose, the same types of protection apply for radiologic technologists regardless of the imaging method. The control booth is a safe area behind secondary barriers. If the construction of the room is up to code, the radiation in this area will be held to a maximum of 100 millirem or 1 millisievert per week. The control panel for the X-ray tube contains exposure controls and an exposure button that can be connected by a cord so that the technologists can hold it in his or her hand. The cord should not be long enough to allow the technologist to enter the imaging room while making an exposure. For the safety of both, the technologist and the patient, there should be a leaded glass window that allows the technologist to watch the patient without being exposed to radiation. Basic radiography rooms are used for many types of examinations and generally the X-ray tube can be pointed in any direction. The technologist who is responsible for insuring the tube is never pointed in an open doorway, the control booth wall or window, or anything other than the image receptor. Also, focusing the beam collimators and using the smallest field of view necessary ensures that the patient and technologist are exposed to the least amount of radiation possible. If the patient does need help remaining still during an exam, Patient restraint devices can be used instead of having a staff member hold the patient in place. Some exam tables have safety straps and wall units have stabilization bars. Most diagnostic radiography departments also have sandbags that can be used for several purposes including weighing down patient's arms for a cervical spine study, securing a pole that the patient is holding for stabilization, and keeping an extremity in a particular position. Adhesive tape should only be used as a last resort to keep a patient or body part still and only of the patient gives consent. If personal assistance is necessary, a member the patient's family should be the first choice to remain in a room during an exam provided that that relative is not pregnant and does not suspect that she may be. If a member of the family isn't available, a hospital employee who is not generally not exposed to occupational radiation, such as a nurse, can help. Radiologic technologist should be the last choice to help a patient stay still during an examination. Finally, whoever remains with a patient in the exam room for this purpose, hospital staff member or not, should be advised of possible radiation exposure and should be given minimum of a lead apron with a thyroid shield and leaded eyewear if needed.

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Duration: 8 minutes and 51 seconds
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Language: English
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Posted by: omar.hassan on Nov 3, 2015

Radiation_Protection_in_Medical_Imaging_(Part 4)

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