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RAD141-Chap 2d

RAD141 - Chap 2d - Radiation Protection

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