Radiology Safety Certification Course

Transcription

1 Radiology Safety Certification Course Laurie Carter, D.D.S., Ph.D. Virginia Commonwealth University School of Dentistry I. Historical Overview A. X-Rays discovered by Wilhelm Roentgen on Nov. 8, 1895 by accident B. First x-ray tube known as a Crooke s Tube or Cathode Ray Tube 1. Evacuated tube with two electrodes (cathode and anode) through which an electrical current is passed 2. Modern day x-ray tubes still work on the same basic principle as the Crooke s Tube II. III. IV. What is Radiation? A. A form of electromagnetic energy emitted and transferred through matter B. Travels at the speed of light C. Has a wavelength D. Has a frequency E. Has no mass or charge How is Radiation Produced? A. Three requirements: 1. Source of electrons 2. A way to accelerate the electrons 3. A way to decelerate the electrons very quickly B. X-Ray Tubes have three main parts: 1. Cathode: source of electrons a. Negatively charged b. Contains a filament which, when heated, spews off electrons 2. Anode: attracts the electrons at a great speed, the accelerator a. Positively charged; attract the negatively charged electrons, which gather speed as they race from cathode to anode. b. Contains a target (focal spot) which the electrons smash in to, releasing their energy as 1% radiation and 99% heat 3. Pyrex Glass Tube: surrounds the anode and cathode a. Maintains a vacuum which prevents air from interfering with the traveling electrons Radiobiology A. Three possible types of interaction of x-rays with matter: 1. Scatter x-ray hits patient, but does not enter tissue. New photon of lower wavelength (energy) travels in a different direction. Source of fog on radiograph and source of useless radiation to patient 2. Absorption Some/all of x-ray energy absorbed by tissue. Removes photons from beam, results in white (radiopaque) areas on the image metallic restorations, cortical bone/enamel 3. Transmission Photon passes completely through patient and strikes image receptor, resulting in black (radiolucent) areas on the image Revised 26 Jan

2 B. Ionizing Radiation 1. Excitation 2. Ionization radiation which can eject an orbital electron from its shell producing an ion pair free radical production 3. Breakage of Molecular Bonds 4. Direct and Indirect Effects of Radiation C. Radiosensitivity is determined by four factors: 1. the metabolic state of the tissue a. The faster cells are dividing in a tissue, the more radiosensitive that tissue is (Law of Bergonie and Tribondeau) Radiosensitive bone marrow stem cells, sperm, ova. Radioresistant nerve, muscle 2. The rate at which the radiation is delivered (protraction) a. The more radiation delivered at one time, the more cellular damage occurs 3. The amount of time between exposures (fractionation) a. The more time between exposures, the more a tissue can repair itself 4. The size of the area exposed a. full-body exposure is more damaging than exposure to a smaller area D. Specific tissue sensitivities 1. Most sensitive cells to radiation damage: bone marrow stem (blood) cells 2. Reproductive cells very sensitive to radiation sperm and ova 3. Corneas and thyroid gland also very sensitive E. Visible effects of radiation exposure 1. Erythema-appears as a sunburn; first response to large dose radiation exposure 2. Moist desquamation-the skin blisters and peels off; follows erythema in larger exposures F. Short-term somatic effects: responses seen within days or weeks of a substantial exposure which can lead to death 1. Bone Marrow Syndrome: reduction of white blood cells, anemia, hemorrhage death in 2-3 weeks 2. Gastrointestinal Syndrome: diarrhea, loss of apatite, lethargy death in 7-10 days 3. Central Nervous System Syndrome: brain edema leads to lethargy, seizures, coma death in 2-3 days V. Quack Medicine and Dangerous Consumer Goods A. Radium ore healing pad B. Radium water C. Radium bath salts D. Radium suppositories E. Radium girls F. Shoe-fitting fluoroscopes G. Red Fiesta ware H. Refrigerator/freezer deodorizer I. Camping lantern mantle J. Vaseline glass K. Spark plugs L. TIG welding rods M. Radon egg, ceramic disks, health card N. Fertilizer O. Record album dusters Revised 26 Jan

3 P. Radon in drinking water Q. Salt substitute R. Tritium glow lights S. Smoke detectors VI. VII. VIII. Types of Radiation A. Natural 1. Terrestrial radon accounts for ~52% of the annual exposure of the U.S. population to radiation 2. Cosmic 3. Foodstuff B. Man-Made 1. Radioactive fallout 2. Nuclear fuel production & usage 3. Consumer products 4. Medical radiation - ~11% of annual exposure of the U.S. population to radiation, and dental is a very small component of that figure Measuring Radiation A. Standard International Units 1. Gray, Sievert, Coulombs per kg B. Traditional System 1. Rad, Rem, Roentgen C. Gray/Rad: describes amount of radiation absorbed by any medium D. Rem/Sievert: radiation equivalent in man (amount of occupational exposure). Rem is the unit used to measure on-the-job radiation exposure to dental personnel E. Roentgen/Coulombs per kg: radiation exposure in air F. Conversion between the systems: 1. 1 Standard International Unit = 100 Traditional Units Radiation Exposure A. Safe radiation exposure levels are those which do not cause a change in the genetic makeup of a cell. 1. No amount of radiation exposure is completely safe-all has the potential to cause cellular damage B. Maximum Permissible Dose (MPD) for dental team = 5 Rem per year. This level is considered safe C. Average dental doses: 1 PA = mr D. ALARA: As Low As Reasonably Achievable 1. Keep radiation exposure to you and your patient ALARA E. Radiographic studies and comparable background exposures Revised 26 Jan

4 IX. Image Critique How do we decide if an image is acceptable? A. Three main factors: positioning, density, and contrast 1. Positioning a. Is the desired anatomy displayed on the film? b. Is the anatomy displayed in a way that is diagnostic? (No overlaps, cone cuts, etc.) 2. Density a. Is the film too light or too dark? 3. Contrast a. Are the differences between the shades of black, white, and grey sufficient to demonstrate differences in adjacent tissues? B. Specific Criteria 1. Periapical a. Entire tooth/teeth visible b. at least 2 mm beyond the apex is visible c. Minimal distortion 2. Bitewing a. All molars and distal 2 nd premolar visible on molar BW b. All premolars and distal of canine visible on premolar BW c. Interproximal spaces are open d. Crowns and bone levels are visible (50% Rule) 3. Panoramic Image a. Entire mandible, condyles, and all dentition are visible b. Positioning displays anatomy clearly Revised 26 Jan

5 X. The X-Ray Beam Alignment (Alignment of the beam with the film) A. Ideal beam alignment places the beam parallel with the film. B. Ideal beam alignment minimizes distortion. C. Two types of alignment: horizontal and vertical 1. Horizontal alignment: perpendicular to the occlusal plane a. Correct horizontal alignment directs the x-ray beam straight through the contacts b. Correct horizontal alignment achieves open contacts and minimizes anatomical overlap c. Overlapping on contacts can be caused by improper horizontal angulation or malocclusion (teeth not in proper alignment) 2. Vertical Angulation: movement of the beam up and down in relation to the occlusal plane a. Correct vertical angulation occurs when the beam is perpendicular to the film pack/receptor b. Correct vertical angulation minimizes elongation of palatal cusps, foreshortening of buccal cusps and ensures both palatal and buccal cusps are on the same horizontal plane XI. XII. Controlling the X-ray Beam A. Kilovoltage peak (kvp) refers to the penetrating power of the x-ray beam and is the primary controlling factor of radiographic contrast. Increasing the kvp produces x-rays which penetrate the tissues more deeply. Lower kvp produces images with higher contrast, while higher kvp produces images with lower contrast. Contrast is the ability to see differences between adjacent tissues B. Milliamperage (ma) refers to the quantity of radiation coming out of the tube and is the primary controlling factor or radiographic density C. Exposure time is the length of time radiation is being emitted from the x-ray tube. D. kvp, ma and exposure time ALL contribute to image density, with ma having the greatest degree of control over density Radiation Protection A. Protecting Yourself 1. Distance: the farther you are from the radiation source, the safer you are. a. 6 feet is a safe distance from most x-ray tubes. 2. Shielding yourself: leaded barriers or walls, cinderblock, 2-3 gypsum drywall 3. Monitor your exposure with a badge (dosimeter) quarterly readings recommended B. Protecting your patient 1. Collimation - Square/rectangular cones: reduce exposure by 50% over round cones 2. Filtration at least 2.5 mm Al in BID 3. Long BID reduces exposure over short BID 4. Thyroid collars required for pediatric patients, when they will not interfere with conduct of the exam 5. No repeats Revised 26 Jan