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RAD141-Chap 2d
RAD141 - Chap 2d - Radiation Protection
| Question | Answer |
|---|---|
| What is the technologist's responsibility w/regard to radiation? | ALARA - the technologist must ensure that the radiation dose to both the patient and the technologist is kept as low as reasonably achievable |
| What is a roentgen? | a measurement of radiation exposure in air, measured by the amount of ionization in a given unit of air; abbreviation = R |
| What are rads and rems? | units of dose -> ionization w/in tissue or described as energy absorbed by tissue; rads -> patient doses; rem -> used or radiation protection purposes |
| How are roentgens, rads, and rems related? | they are equivalent; 1 R = 1 rad = 1 rem |
| What is the correct term for maximum permissible dose? | dose-limiting recommendations |
| Whatr is the annual dose limit for occupationally exposed workers? | 5 rem (50mSv) of whole-body effective dose (ED)/year; aka annual effective dose limit |
| What is the annual dose limit for the general public (for frequent and infrequent exposure)? | 0.1 rem (1 mSv) /year for continuous or frequent exposure; 0.5 rem (5 mSv)/year for infrequent exposure |
| What is the cumulative lifetime ED for an occupationally exposed worker? | 1 rem (10 mSv) times the years of age; but, technologists must limit their exposure to the least amount possible, or even less than the allowable 5 rem (50 mSv) /year |
| When should a qualified radiation protection officer be utilized? | when the potential for exposure = or exceeds 0.1 rem/year |
| What is the dose limit for minors? | individuals uner 18 years of age should not be employed in situations in which they are occupationally exposed; ED limit for minors is same as general public (0.1 rem/year) |
| What are the SI units for roentgens, rads, and rems? | Roentgen -> Coulombs/kg of air (mult by 2.58 * 10^-4); rad -> Gray (Gy) (mult by 10^-2); Rem -> Seivert (SV) (mult by 10^-2) |
| What is an mrad? | 10^-2 or 0.01 mGy; 1mGy = 100mrad; mrads are used for patient doses |
| How are dose limits measured? | by rem or Seivert (Sv); 1 rem = 0.01 Sv or 10 mSv; 1 mSv = 0.1 rem |
| What is the recommended maximum equivalent dose to the fetus? How should this be monitored? | 0.05 rem or 50 mrem (0.5 mSv) duraing any 1 month and 0.5 rem or 500 mrem (5mSv) for the gestation period; a 2nd film badge should be worn under the lead apron at the abdomen |
| What are TLD badges and when are they required? | TLD -> thermoluminescent dosimetry badges must always be worn by all personnel who have the potential of receiving more than 1/4 the recommended dose limit; must be worn at waist or chest level, except in fluoroscopy |
| Where should TLD badges be worn in fluoroscopy? | at the collar area outside the lead apron |
| How often should film badged be changed and read? TLD badges? | Film badges are changed and read monthly; TLD badges at least every 3 months |
| What are 4 ways ALARA can be achieved? | 1) always wear a monitoring device; 2) never hold a patient during exposure; 3) close collimation, filtration of primary beam, optimum kV techniques, high-speed screens and film, and minimum repeat exams; 4) time, distance, and shielding principle |
| What are the 2 types of "dosage" measurements for a patient? | SEE -> skin entrance exposure -> highest numeric value, but the least biologically significant; ED -> effective dose -> takes into account the dose to all organs and their relative risk of becoming cancerous |
| Which radiographic procedure has the highest ED for males? for females? | males -> AP unshielded hip (ED=84) (with shielding, ED = 14); females -> AP thoracic spine on a 14 x 17 film w/o breast shields (ED=63;w/ 7x17 film -> ED=35) |
| Why do fluoroscopic procedures generally involve much higher patient doses than conventional "overhead tube" diagnostic exams? | because of the need to penetrate the barium or iodine contrast media and the time required to manipulate the media in the patient; however, volume of tissue exposed is fairly small |
| What impact does magnification mode have on patient dosage? | increases the dose rate, but decreases the volume of tissue exposed |
| How can dosage be reduced in fluoroscopy? | pulsed fluoroscopy may be used to reduce dose in proportion to the # of pulses used per second; spot film doses can be reduced by using photospot cameras or digital fluoroscopy |
| How can the technologist protect themselves during fluoroscopy procedures? | the intensifier tower, tower lead drapes, Bucky slot shield, x-ray table, patient foot rest, and the radiologist provide shielding; least amount of exposure is 4 feet away from the table and behind the radiologist |
| What type of radiation is the technologist exposed to during fluoroscopy? | scatter radiation |
| Where is the scatter radiation greatest in fluoroscopy? | in the immediate region of the patient close to the table on each side of the radiologist |
| What type of protection must be worn during fluoroscopy? | a lead apron must be worn; a 0.5 mm lead equivalent apron reduces scattered radiation to the majority of the body by 10 or more times, enough to reduce risks well below recommended dose limits |
| Should thyroid shields and leaded gloves and glasses be worn during fluoroscopy? | thyroid shields can be worn when available, but offer little additional protection; gloves and lead glasses are not necessary if recommended practices are followed |
| What is the federal standard for exposure rates in fluoroscopy? | 10 R/min; most modern equipment has an average fluoroscopy rate between 3 and 4 R/min |
| What 7 ways can the technologist minimize patient dosage? | 1)mimimize repeat radiographs; 2)correct filtration; 3)accurate collimation; 4)specific area shielding; 5)protection for pregnancies; 6)use of high-speed film-screen combinations; 7)minimize patient exposure thru selecting projections & exposure factors |
| How can patient exposure be minimized by proper selection of projections & exposure factors? | use of higher kV, lower mAs; use of PA rather than AP projections to reduce dose to anterior upper thoracic region (thyroid, neck, breasts); use of techniques consistent w/system speed for digital radiography (confirmed by exposure index values) |
| What are the 2 major reason for unnecessary repeat radiographs? | 1) poor communication between technologist & patient (motion); 2) carelessness in positioning & selection of incorrect exposure factors |
| What does filtration accomplish? | reduces patient exposure by absorbing most of the lower-energy "unusable" x-rays -> hardening of the x-ray beam => increase in effective energy or penetrability of the x-ray beam |
| What is inherent filtration? | built-in filtration from the structures making up the x-ray tube itself; approx 0.5 mm aluminum (Al) equivalent |
| Where does added filtration come from? | the amount of filtration between the x-ray tube and the collimator, and within the collimator itself |
| What is the minimum total filtration? | minimum inherent plus added filtration is 2.5 mm Al equivalent for equipment producing 70kV or greater |
| What metals are most commonly used in filter? | Aluminum is most commonly used in filters for diagnostic radiology; molybdenum (Mo) most often used in mammography |
| How does accurate collimation reduce patient exposure? | by limiting the size and shape of the x-ray beam to only the area of clinical interest, reducing the volume of tissue directly irradiated and by reducing the accompanying scatter radiation |
| What are the safety standards regarding collimator accuracy? | must be accurate to within 2% of the SID |
| How does divergence affect collimation? | the illuminated field size as it appears on the patient's skin surface will appear smaller than the actual size of the anatomic area; exp evident on a lateral thoracic or lumbar spine (consideral distance from the skin surface to the IR) |
| What is positive beam limitation? | PBL was required between 1974-1993 in the US/Canada; automatical collimation of the usefule x-ray beam to the film size, consisting of sensors in the film cassette holder, automatically signalling the collimator to adjust x-ray beam to film/IR size |
| If PBL is in use, should manual collimation ever be used? | the operator can manually reduce the collimation field when the IR is larger than the critical area being radiographed and in exams of upper & lower limbs taken tabletop wherein the PBL is not activated |
| What are 3 reasons for 4-sided collimation? (And an extra reason) | 1)reduces patient exposure; 2)improves image quality; 3)visible collimation on 4 sides proves maximum collimation did occur (if not visible, can't prove that primary beam was restricted at all); also, 4-sided collimation provides a check of CR location |
| What is the collimation rule? | collimation should limit the exposure field to only the area of interest and collimation borders s/b visible on the IR on all 4 sides (if the IR size is large enough to allow this w/o "cutting off" essential anatomy |
| When is specific area shielding required? | when radiosensitive tissue or ograns (thyroid gland, breasts, and gonads) are in or near the useful beam |
| What is the most common and most important area shileding? | gonadal shielding -> protects the reproductive organs from irradiation when they are in or near the primary beam |
| What are the 2 types of specific area shielding? | shadow shields and contact shields |
| What are shadow shields? | they are attached to the collimator, placed between the x-ray tube & the patient, casting a shadow of the shield over the specific areas being sheilded |
| What are gonadal contact shields? How are they constructed? | most commonly used for patients in recumbent positions; minimum 1-mm lead equivalent when placed in the primary x-ray field |
| Besides gonadal contact shields, how else can the gonads be protected from scatter and/or leakage radiation? | larger vinyl-covered lead shields of 0.5-mm lead equivalent placed over the gonadal area in general |
| Where are male conadal shields placed? How are they shaped? | distally to the symphysis -> upper margin at the symphysis pubis; lower area covering the testes and scrotum; smaller sizes for smaller males, children; slightly tapered at the top, wider at bottom |
| Where should gonadal shields be placed on the female adult? | cover ovaries, fallopian tubes, & uterus->4.5-5 inches proximal or superior to the symphysis pubis & 3-3.5 inches each way from the pelvic midline; lower border at or slightly above the symphysis pubis, w/upper border extending just above level of ASIS |
| What shape gonadal shields s/b used on a female? | they s/b wider in the upper region to cover the area of the ovaries; narrower towards the bottom (less obstruction of pelvic/hip structure) |
| What type of gonadal protection s/b used on a 1-yr-old female? | a shield only 2.5-3 inches wide and 2 inches tall, placed directly superior to the symphysis pubis |
| How effective are gonadal shields? | if placed correctly, reduce the gonadal dose 50% - 90% if the gonads are in the primary x-ray field |
| What are the 3 summary rules for specific area sheilding? | s/b used on all potentially reproductive-age patients; s/b used when radiation-sensitive areas lie w/in or near (2 inches) primary beam unless such shielding obscures essential diagnostic info; accurate beam collimation & careful positioning must be used |
| When is radiation exposure most critical during pregnancy? | During the 1st 2 months |
| What former rule was designed to protects potential early pregnancies? | The 10-day or LMP rule -> all radiologic exams involving the pelvis & lower abdomen s/b scheduled during the 1st 10 days after the onset of menstruation |
| Why was the 10-day rule abandoned? | because of the potential harm to the woman in delaying essential x-ray procedures |
| Are x-rays now allowed outside of this 10-day period? | Yes, although higher dose exams of the pelvic area or fluoroscopy procedures can be delayed a few week if they wouldn't compromise the health of the patient |
| Which exmas result in higher doses to the fetus/embryo? | lumbar spine, sacrum & coccyx, intravenous urogram (IVU), fluoroscopic procedures (abdomen), pelvis, proximal femur and hip, computed tomography; s/b confirmed by referring physician & radiologist 1st |
| Why is the speed of intensifying screens so important? | for all film-screen combinations, over 99% of the radiographic image results from light emitted by the intensifying screens (< 1% form the primary rays) -> speed of intensifying screens has a great effect on x-ray exposure |
| What must be balanced with film speed? | faster film speeds result in some loss of image definition |
| What is common practice for slower (100-speed) screens? For faster-speed screens? | slower 100-speed screens in tabletop procedures (such as upper/lower limbs) as a grid is not used & optimum detail is important; faster-speed screens w/larger body parts (grids & higher exposure techniques are required) |
| What is the film-screen rule? | use the highest speed film-screen combination that results in diagnostically acceptable radiographs; dictated by dept protocol or routine |
Created by:
debmurph
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