Radiation Protection
1. PRINCIPLES OF RADIATION PROTECTION
- Each recent decade has seen remarkable improvements in medical imaging.
Diagnostic ultrasonography appeared in the 1960s, as did the gamma camera.
Positron emission tomography (PET) and x-ray CT were developed in the 1970s.
Magnetic resonance imaging (MRI) became an accepted modality in the 1980s, and now, digital radiography and digital fluoroscopy are rapidly replacing screen-film radiography and image intensified fluoroscopy.
- Unfortunately, radiation injuries occurred frequently. These injuries usually took the form of; skin damage, loss of hair, and anemia. Physicians and, more commonly, patients were injured, primarily because the low energy of radiation then available resulted in the necessity for long exposure times to obtain acceptable images.
- Now, protective devices and apparel, such as lead gloves and aprons, were developed for use by radiologists. X-ray workers were routinely observed for any effects of their occupational exposure and were provided with personnel radiation monitoring devices.
- Radiation protection must be an important consideration during each x-ray procedure.
- The Ten Commandments of Radiation Protection are listed below; 1. Understand and apply the cardinal principles of radiation control: time, distance, and shielding. 2. Do not allow familiarity to result in false security. 3. Never stand in the primary beam. 4. Always wear protective apparel when not behind a protective barrier. 5. Always wear an occupational radiation monitor and position it outside the protective apron at the collar. 6. Never hold a patient during radiographic examination. Use mechanical restraining devices when possible. Otherwise, have family or friends hold the patient. 7. The person who is holding the patient must always wear a protective apron and, if possible, protective gloves. 8. Use gonadal shields on all people of childbearing age when such use will not interfere with the examination. 9. Examination of the pelvis and lower abdomen of pregnant patients should be avoided whenever possible, especially during the first trimester. 10. Always collimate to the smallest field size appropriate for the examination.
- Always practice ALARA: Keep radiation exposures as low as reasonably achievable.
- Minimizing radiation exposure to technologists and patients is easy if the x- radiation imaging systems designed for this purpose are recognized and understood.
1.1. Filtration
- Metal filters, usually aluminum or copper, are inserted into the x-ray tube housing so that low-energy x-rays are absorbed before they reach the patient. These x-rays have little diagnostic value.
1.2. Collimation
- Collimation restricts the useful x-ray beam to that part of the body to be imaged and thereby spares adjacent tissue from unnecessary radiation exposure.
- Collimators take many different forms. Adjustable light-locating collimators are the most frequently used collimating devices.
- Collimation also reduces scatter radiation and thus improves image contrast.
1.3. Intensifying Screens
- Today, most x-ray films are exposed in a cassette, with radiographic intensifying screens on both sides of the film.
- Examinations conducted with radiographic intensifying screens reduce exposure of the patient to x-rays by more than 95% compared with examinations conducted without radiographic intensifying screens.
1.4. Protective Apparel
- Lead-impregnated material is used to make aprons and gloves worn by radiologists and radiologic technologists during fluoroscopy and some radiographic procedures.
1.5. Gonadal Shielding
- The same lead-impregnated material used in aprons and gloves is used to fabricate gonadal shields. Gonadal shields should be used with all persons of childbearing age when the gonads are in or near the useful x-ray beam and when use of such shielding will not interfere with the diagnostic value of the examination.
1.6. Protective Barriers
- The radiographic or CT control console is always located behind a protective barrier. Often, the barrier is lead lined and is equipped with a leaded-glass window.
- Under normal circumstances, personnel remain behind the barrier during x- ray examination.
2. STANDARD UNITS OF MEASUREMENT
- In radiologic science, special physics quantities are measured, those of: exposure, dose, effective dose, and radioactivity.
- The figure below relates them to a hypothetical situation in which they would be used.
- In 1981, the International Commission on Radiation Units and Measurements (ICRU) issued standard units based on SI that have since been adopted by all countries except the United States.
- Becquerel (Bq). The becquerel is the unit of quantity of radioactive material, not the radiation emitted by that material.
- One becquerel is that quantity of radioactivity in which a nucleus disintegrates every second (1 d/s = 1 Bq).
- Megabecquerels (MBq) are common quantities of radioactive material.
- Radioactivity and the Becquerel have nothing to do with x-rays.
- Air Kerma (Kinetic Energy Released in Matter) (Gya).
- Air kerma (Gya) is the unit of radiation exposure or intensity.
- Air kerma is the kinetic energy transferred from photons to electrons during ionization and excitation.
- Air kerma is measured in joule per kilogram (J/kg) where 1 J/kg is 1 gray (Gya).
- Absorbed Dose (Gyt ). Biologic effects usually are related to the radiation absorbed dose. Absorbed dose is the radiation energy absorbed per unit mass and has units of J/kg or Gyt.
- The units Gya and Gyt refer to radiation dose in air and tissue, respectively.
- For a given air kerma (radiation exposure), the absorbed dose depends on the type of tissue being irradiated.
- Sievert (Sv). Occupational radiation monitoring devices are analyzed in terms of sievert, which is used to express the quantity of radiation received by radiation workers and populations.
- Some types of radiation produce more damage than x-rays. The sievert accounts for these differences in biologic effectiveness. This is particularly important for persons working near nuclear reactors or particle accelerators.
ليست هناك تعليقات:
إرسال تعليق