Final Exam Flashcards

ONCOL 243 - Radiation Safety. University of Alberta

The filters contained in a film badge personnel dosimeter are generally composed of which two metals?

Aluminum or Copper

What is the maximum period of time that a thermoluminescent dosimeter (TLD) may be

worn as a personnel dosimeter?

3 Months

What do optically stimulated luminescence dosimeters (OSLs), thermoluminescent dosimeters, film badge dosimeters, and pocket ionization chambers have in common?

all devices are used for personnel monitoring

what device is known as a cutie pie

ionization chamber-type survey meter

Which device contains an Aluminum Oxide Detector

OSL dosimeter

When the sensing crystals contained in the TLD are exposed to ionizing radiation, what occurs?

Some of the electrons in the crystalline lattice structure of the LiF molecule absorb energy are excited to a higher energy level or band.

What makes the optically stimulated luminescence dosimeter ideal for monitoring employees working in low-radiation environments and for pregnant workers?

the increased sensitivity

which item is not a basic component of a film badge dosimeter

a. radiographic film packet

b. durable plastic film holder

c. charged electrodes

d. assortment of metal filters

charged electrodes

which personnel dosimeter resembles an ordianry fountain pen externally?

pocket ionization chamber

three disadvantages of pocket ionization chambers as personnel dosimeters

1. mechanical shock causes pocket chambers to discharge

2. permanent legal record of personnel exposure cannot be obtained

3. false high readings may be obtained if pocket dosimeter is not read each day

what two components of a Geiger-Muller detector alterts the operator to the prescence of radiation

an audio amplifier and a speaker

are all field survey instruments equally sensitive to detecting ionizing radiation?

no

ionization chambers are used by medical physicists to perform standard measurements. List three measurements ionization chambers can be used for

1. x-ray ouput (in mR/mAs)

2. reproducibility and linearity of output

3. timer accuracy

what should be part of an employment record of all radiaiton workers?

a record of exposure recorded by personnel dosimeters

what should be given to a radiation worker on termination of their employment

a summary of their occupational exposure report

why is the front of the white paper packet on a dosimeter color coded?

to facilitate correct usage and placement of the badge on the body of occupationally exposed personnel

list three different materials that are incorporated into the detector packet of OSL dosimeters

1. aluminum

2. copper

3. tin

what device can be used to provide immediate exposure readout for a radiation worker working in a cardiac catheterization laboratory

a pocket ionization chamber

what is a disadvantage of optically stimulated dosimeters?

exposure is not determinable on day of occurance

whenever the letter ‘M’ appears under the current monitoring period or in the cumulative columns of a personall monitoring report, it signifies ….

equivalent dose below the minimum measureable radiation quantity was recorded during that time

the optically stimulated dosimeter is ‘read out’ by using

laser light at selected frequencies

list three advantages of OSL dosimeters

1. can be used for up to a year

2. lightweight, durable, easy to carry

3. integrated, self-contained, preloaded packets

which of the following is not an x-ray limitation device

a. aperature diaphragm

b. collimator

c. filter

d. extension cylinder

c. filter

When the speed of screen-film systems doubles, for example, when changing from a 200- speed to a 400-speed system, what happens to patient exposure?

Patient exposure is reduced by half.

Sharper size restriction of the radiographic beam is achieved when a cone or cylinder is:

longer

When using digital fluoroscopy systems, making use of the last-image-hold feature can …

be an effective dose reduction technique

what is the purpose of radiographic beam filtration?

to increase beam hardness, thereby reducing patient skin dose and dose to superficial tissues

Depending on the area of the body being examined with a fluoroscopic image intensification system, for adult patients, a range of ______ kVp is generally used.

75-110 kVp

When performing a mobile fluoroscopic procedure, to reduce the radiation exposure to the patient, the radiographer must use a minimal source-skin distance of …

30 cm

what are three benefits of electronically amplifying an image using an intensification system in fluoroscopy?

1. increased image brightness

2. saving of time for radiologist

3. reduced patient dose

Current federal standards limit entrance skin exposure rates of general-purpose intensified fluoroscopic units to a maximum of ______________ measured at tabletop with the image intensifier entrance surface at a prescribed 30 cm above.

100 mGy_a/min

During a fluoroscopic examination, a resettable cumulative timing device times the x-ray beam-on time and sounds an audible alarm or temporarily interrupts the exposure after the fluoroscope has been activated for what length of time?

5 minutes

To visualize smaller and lower contrast objects during interventional procedures, high-levelcontrol fluoroscopy uses exposure rates that are ____________ those normally used in routine fluoroscopy

higher than

when obtaining a dorsoplantar projection of the foot, which of the type of filters should be used to provide the greatest uniform density?

wedge filter

A radiographer uses a high-speed, rare-earth screen-film system with optimal technical exposure factors to obtain PA and lateral radiographs of a 2-year-old child’s chest. To maximize reduction of radiation exposure to the patient following adequate immobilization, the radiographer should:

collimate the x-ray beam so that it is smaller than the margins of the image receptor and shield the child’s reproductive organs

Federal government specifications recommend a minimum total filtration of _______________ for stationary (fixed) fluoroscopic x-ray units operating above 70 kVp.

2.5 mm aluminum equivalent

Compared with the traditional material in the front of a cassette (aluminum or cardboard), the cassette front containing the carbon fiber absorbs approximately ______ as much radiation, resulting in a __________ dose for the patient because ________ radiographic techniques are required to produce the recorded image.

half, lower, lower

In standard image intensification fluoroscopy, an x-ray beam half-value-layer (HVL) of 3 to 4.5 mm aluminum is considered acceptable when peak kilovoltage ranges from

80-100 kVp

When an exposed computed radiography imaging plate is ready to be processed, an imaging reading unit is used to scan the photostimulable phosphor imaging plate with a helium-neon laser beam. This results in the emission of violet light that is changed into an electronic signal by a device called …

a photomultiplier tube

Computed radiography, because of its higher exposure latitude, makes grid use on the pediatric population

less necessary than was previously believed

CR imaging has greater ____________ flexibility than conventional screen-film radiography.

kilovoltage

list three procedures that require extended fluoroscopic time

1. biliary drainage

2. stent/filter placement

3. urinary/biliary stone removal

how is luminance determined

by measuring the concentration of light over a particular field of view

When settings are changed from one mA to a neighboring mA station, the most that linearity can vary is

10%

The control panel, where technical exposure factors are selected and seen on indicators by the equipment operator, must be located …

behind a suitable protective barrier that has a radiation absorbent window that permits observation of the patient during any procedure

Which of the following materials is commonly used in the tabletop of a radiographic examination table to make the tabletop as radiolucent as possible so that it will absorb only a minimal amount of radiation, thereby reducing the patient’s radiation dose?

carbon fiber material

what effect does a repeat image have on the radiation dose received by the patient?

The patient’s skin and possibly the gonads receive a double radiation dose.

During a radiographic examination, what three technical exposure factors and filtration reduce patient radiation dose?

• higher kVp

• lower mAs

• increased filtration

what two practices will minimize radiaiton exposure for a pregnant woman

1. select technical exposure factors that are appropraite for the part of the body imaged

2. Precisely collimating the radiographic beam to include only the anatomic area of interest and shielding the lower abdomen and pelvis when this area does not need to be included in the area to be irradiated

According to the American College of Radiology (ACR), abdominal radiologic examinations that have been requested after full consideration of the clinical status of a patient, including the possibility of pregnancy, need …

not to be postponed or selectively scheduled

Which type of gonadal shielding provides the best protection for a male patient when AP, oblique, and lateral projections are obtained?

Shaped contact shield containing 1 mm of lead

Specific area shielding may be selectively used during some x-ray procedures to protect which three parts of the body?

1. lens of the eye

2. breast

3. gonads

what are the most commonly used sensing devices to measure skin dose directly

thermoluminescent dosimeters

what is the genetically significant dose (GSD) for US population?

0.20 mSv

what is always the first step in protecting reproductive organs?

Adequate and precise collimation of the radiographic beam to include only the anatomy of interest

When automatic exposure control (AEC) is not used, then to ensure uniform selection of technical x-ray exposure factors, what do imaging departments do?

use standardized technique charts for each x-ray unit

poorly processed imaged on radiographic film will …

deteriorate over time

In fluoroscopy, the amount of radiation that a patient receives is usually estimated by measuring the radiation exposure rate at tabletop and multiplying this by …

the fluoroscopy time

can the radiaiton dose to an organ (such as bone marrow) be measured directly?

no, it can only be estimated

Digital mammography units with the ability to enhance contrast with image gray-level manipulation offer improvements to which patients?

patients with dense breast tissue

during mammography axillary projections should be done only on the request of …

the radiologist

what happens if a child is placed in a CT scanner and adult protocols are used

the child will receive higher dose than the adult

what is the biggest problem in diagnostic pediatric radiography

patient motion

what should the radiologic physicist do if a pregnant patient is inadvertently irradiated

perform the calculations necessary to determine fetal dose

Studies of groups such as the atomic bomb survivors of Hiroshima have shown that damage to newborns is unlikely for doses below …

0.2 Gy

Because most medical procedures result in fetal exposures is less than _____ Gy, the risk of abnormality is ____

0.01 Gy, small

list 3 nonessential radiologic procedures

1. a chest x-ray on scheduled admission to the hospital

2. lumbar spine x-ray as part of preemployment physical exam

3. whole body multislice CT scan

what three factors must be considered when selecting radiographic exposures

1. mass per unit volume of tissue in area of interest

2. effective atomic number and electron densities of tissue involved

3. type and quantity of filtration used

list three x-ray procedures with increased risk of exposure for radiographers

1. mobile c-arm fluoroscopy

2. interventional procedures that use high-level-control fluoroscopy

3. mobile radiographic exams

Because occupational exposure of the radiographer can be kept as low as reasonably achievable (ALARA) through individual monitoring and other protective measures and the use of protective devices and because exposure from radiation-related jobs will not alter the ______________________, radiation workers may receive a larger ________ than members of the general population

genetically significant dose, equivalent dose

In terms of occupational risk, radiography may be compared with the occupational risk associated with what other jobs?

Other industries considered reasonably safe, such as government and trade

whenever scattered radiation decreases, the radiographer’s exposure

decreases

what two adjustments decrease the production of scatter radiation

1. decrease kVp

2. increase mAs in compensation

During which two x-ray examinations should a radiographer always wear a thyroid shield?

1. fluoroscopy

2. special procedures

While standing behind the control-booth barrier, a radiographer makes a radiographic exposure. The x-rays scattered from the patient’s body should ____________________.

scatter a minimum of two times before reaching any area behind the control-booth barrier

Which of the following is another term for use factor (U)?

The beam direction factor

The annual effective dose limit for individual members of the general population not occupationally exposed is ___________ for continuous or frequent exposures from artificial sources other than medical irradiation and natural background and ____________ for infrequent annual exposure.

1 mSv, 5 mSv

A spot film device protective curtain, or sliding panel, of a minimum thickness of 0.25-mm lead equivalent should normally be positioned between the fluoroscopist and the patient to intercept which of the following type of radiation?

scattered radiation from the tabletop

How does the intensity of the x-ray beam change when the distance from the source of radiation and a measurement point is tripled?

The intensity of the x-ray beam decreases to one-ninth of its original value according to the inverse square law.

What is the term for the proportional amount of time during which the x-ray beam is energized or directed toward a particular barrier?

use factor

The maximum weekly permitted equivalent dose for a controlled area must not exceed

1 mSv per week

When a radiologic technologist declares her pregnancy to her employer, what happens?

She continues to perform her duties without interruption of employment, provided that she has received radiation safety counseling and follows established radiation safety practices.

what three parts of a diagnostic x-ray unit should a radiographer avoid touching while exposure is in progress

1. tube housing

2. collimator

3. high-tension cables

When doors to radiographic and fluoroscopic rooms are closed during radiation exposures, a substantial degree of protection is provided for persons in areas adjacent to the room door. This is because in most facilities room doors have attenuation for diagnostic energy x-ray equivalent to that provided by _______ mm of lead.

0.8 mm of lead

When the time spent in a higher radiation area is reduced or limited, occupational exposure …

is also reduced

Diagnostic imaging personnel receive the highest occupational exposure during which three procedures?

1. fluoroscopy

2. mobile radiography

3. special procedures

If the peak energy of the x-ray beam is 100 kVp, a protective lead apron must be the equivalent to at least ______

0.25 mm thickness of lead

For C-arm devices with similar fields of view, the dose rate to personnel located within a meter of the patient is comparable to what other radiographic scan

routine fluoroscopy

Protective eyeglasses with optically clear lenses should contain a minimal lead equivalent protection of …

0.35 mm of lead

_______________ is the radiation output weighted time that the unit is actually delivering radiation during the week.

Workload

To ensure that the lifetime risk of occupationally exposed persons remains acceptable, the lifetime effective dose in mSv should not exceed …

10 x the occupationally exposed person’s age in years

secondary leakage includes what two kinds of radiaiton

1. scatter radiation

2. leakage radiation

Who determines the exact shielding requirements for a particular imaging facility?

medical physicists

therapeutic radioisotopes are characterized by …

relatively long half-lives

Iodine-125 (125I) in the form of titanium-encapsulated cylindrical seeds has been used in what kind of tumors?

prostate cancers defined within the prostate cland

How many protons and neutrons does Te-125 have?

52 protons

73 neutrons

what is the half-life of Technetium-99m

6 hours

A neutron transforms itself into a combination of a proton and an electron via what process

beta decay

how thick is the rolling lead shield that is positioned between the patient and the hosptial staff during I-131 therapy

1 inch thick

Diagnostic techniques in nuclear medicine typically make use of ___________ radioisotopes as radioactive tracers.

short lived radioisotopes