Management of Imaging Personnel and Radiation Dose

Flashcards covering key concepts related to the management of imaging personnel and radiation dose.

Annual Occupational Dose Limit

50 millisievert (mSv) for whole body exposure as per federal government NCRP recommendations.

General Public Dose Limit

1 mSv for continuous or frequent exposures from artificial sources, and 5 mSv for infrequent annual exposure.

ALARA

As low as reasonably achievable

Cardinal Principles of Radiation Protection

Time, Distance, and Shielding.

Primary Protective Barrier

Prevents direct radiation or unscattered radiation from reaching personnel or the public; typically made of 1.6 mm lead.

Secondary Protective Barrier

Protects against leakage and scatter radiation; typically made of 0.8 mm lead.

Occupancy Factor

The fraction of the week during which a space beyond a barrier is occupied, influencing shielding requirements.

Workload (W)

Reflects the unit's radiation-on time used for determining barrier shielding.

Controlled Area

Region adjacent to an x-ray room used only by occupationally exposed personnel.

Leakage Radiation

Radiation generated in the x-ray tube that does not exit the collimator opening but penetrates through the tube housing.

Dose Reduction Method & Techniques

Avoid repeating images

The patient as a source of scattered radiation

For Dose Reduction Method & Techniques; At what angle do you stand to reduce the chances of scattered radiation?

90 degrees

The scattered x-ray intensity is reduced by ____ the intensity of the primary x-ray beam when standing at a 90 degree angle to the patient (primary beam), at a distance of 1m.

1/1000

What is the protective apparel thickness of a glove?

0.25mm of lead equivalent

What is the protective apparel thickness of a Apron (NCRP recommendation)?

0.5 mm of lead equivalent

What is the protective apparel thickness of a thyroid shield?

0.5 mm of lead equivalent

What is the protective apparel thickness of a protective glasses?

0.35 mm of lead equivalent

What is the protective apparel thickness of a protective curtains?

0.35 mm of lead equivalent

The monthly EqD to the embryo-fetus shall not exceed _____

0.5 mSv

If a radiographer stands 2 m away from an x-ray tube and receives an exposure rate dose of 6.0mGya/hr, what will the exposure rate dose be if the same radiographer moves to stand 4m from the x-ray tube?

1.5 mGya/hr

what is the difference between the primary protective barrier and a secondary protective barrier (what does each barrier protect against)?

primary barrier protects against primary beam
secondary barrier protects against leakage and scatter

What is the thickness for a primary protective barrier, and what is the thickness for a secondary protective barrier?

primary - 1.6 mm or 1/16 th
secondary - 0.88 mm or 1/32

The region adjacent to a wall of an x-ray room can be controlled or uncontrolled.

A. who wouldin a controlled area:

B. Who makes up the uncontrolled area:

C. What is the weekly MPED for controlled area?

D.What is the weekly MPED for an uncontrolled area?

A. occupational

B. General public

C. 1000 microSv / 1mSv

D. 2 micro SV

Scattered Radiation - Occupational Hazard

By reducing the size of the radiographic beam (collimate), this reduces the # of x-ray photons available to undergo Compton scatter which __

reduced occupational dose

What does filtration of the diagnostic beam do?

removes long and low-energy wavelengths, reducing patient dose.

Protective apparel

protects personnel from both leakage and scatter radiation - secondary radiation

Lead aprons can be made with as little as ____ lead equivalent.

0.25 mm

The NCRP requires our leads to be ___ lead equivalent

0.5 mm

technical exposure factors

increasing kVp techniques, requires less mAs, less scatter production

Using higher kVp increases the mean energy of the photons comprising beam which__

decreases large angle scatter

repeats in digital imaging

try to position correctly the first time

Patient Restraint

The radiographer must never ____ _____ to restrain a patient during a radiographic exposure.

stand in the primary beam

Use patient restraints to _____ the patient when possible

immobilize

For patient restraint, use ______ person, preferably male or person of non-childbearing age to hold when necessary 

non-occupational

Protection for pregnant personnel - Imaging departement protocol

worker should declare pregnancy

RSO will provide fetal radiation dosimeter

Additional dosimeter will ensure that the _____ EqD to the embryo-fetus does not exceed _____

monthly

0.5 mSv

ALARA guidelines have all workers rotating equally to distribute radiation exposure risk ______ to all employees

evenlyand minimize risk

If a pregnant worker is pulled from a rotation it __

increases the rest of the staff’s overall risk

A declared pregnant radiographer ______ need to be reassigned to a lower radiation exposure position.

does not

Time is important in ___

fluoroscopy

Fluoroscopic x-ray units are equipped with ____

5 minute timer alert

Time

The amount of radiation a worker receives at a particular location is ______ to the length of time the individual is in the path of ionizing radiation.

directly proportional

Distance

most effective means of protection from ionizing radiation

The further you stand away the ____

less dose you receive

Distance- Inverse Square Law

Expresses the relationship between _____ and _____ of radiation and is a tool to be used in governing the dose receive by personnel

distance, intensity

ISL = The intensity of radiation is _______ to the square of the distance from the source.

inversely proportional 

More distance =

Less intensity

2 x D =

¼ intensity

3 x D =

1/9 intensity

4 x D =

1/16 intensity

Shielding may be used to provide____

protection from radiation

Structural barriers are

lead and concrete

Protective Structural Shielding

used to protect imaging personnel and general public

Lead sheets of appropriate thickness are placed in the walls of the ___

radiography and fluoroscopy rooms

______ determines the exact protection requirements needed

physicist

Two types of barriers

primary and secondary barriers.

Primary protective barriers prevent ____ or _____ _____ from reaching personnel or members of the general public on the other side of the barrier

DIRECT

unscattered radiation

Primary protective barriers consist of

1.6 mm lead (1/16)

Secondary protective barrier protects against ____ and ____

leakage and scatter radiation

Secondary protective barrier consist of 

1/32 in lead (0.8 mm)

The ceiling is considered a

secondary protective barrier

all 4 walls and the floor are considered

primary protective barriers

Control Booth Barrier

protects the radiographer and is considered a secondary protective barrier

Exposure will not exceed a _____

maximum allowance of 1 mSv per week

To reduce dose from scatter one should:

stand far away

wear lead

stand behind the radiologist

Mobile units and Safety

some units have a remote control exposure device

allowing for more distance

Mobile units and Safety

Cord should be long enough to allow radiographer to stand at least ___

2 m from the patient, tube, beam

when possible, stand at a _____ to the xray beam scattering line to reduce intensity of the beam

right angle 90 degrees

Protection During c-arm fluoroscopy

Positioning of the C-arm can _____ or ______ the scatter in the room

increase

decrease

Positioning the c-arm with the x-ray tube over the table and the image intensifier under the table results in higher exposure of the patient and ______

increased scatter radiation

Additional ways to protect during C-arm fluoroscopy aside from limiting the use of boost and magnification or handheld switch.

collimate

last image hold

foot pedal

The exposure rate caused by scatter near the entrance surface of the patient (tube side). exceeds the exposure rate caused by scatter near the exit surface of the patient (image intensifier side) usually by a factor of _____

2-3

lower potential scatter dose is on the ____ of the patient away from the x-ray tube

side

What is the Regular Maximum allowed entrance rate

8.8 cGy/min (10 R/min)

What is the Boost-mode Maximum allowed entrance rate

20-40 cGy/min

Ways Radiologist can reduce exposure

decrease duration of procedure, reduce beam on time

take fewer digital images

reduce use of continuous fluoroscopic mode

use last image hold

Radiologist and physicians performing interventional procedures can be subjected to _____ to the extremities

high doses

NCRP recommends an annual EqD limit to localized areas of the ____

skin and hands of 500 mSv

Radiation sources generated in an x-ray room

primary radiation

scatter radiation

leakage radiation

primary radiation

emerges from the xray tube

scatter radiation

occurs when primary radiation passes through matter.

Radiation output

weighted time that the unit is actually delivering radiation during the week

units of mAs per week or mA-min per week

inverse square law

helps calculate the intensity of the beam which is important in design of radiation safety barriers

Helps determine primary barrier thickness values and secondary barrier thickness value

Use factor

quantity that is used to select fractional contact time

U(secondary) =

1 for all radiation accessible structuresand 1/4 for all other accessible locations.

Because scatter and leakage emerge in all directions in the x-ray room, all surfaces will always be struck by___

some quantity of radiation

Occupancy factor used to modify shielding requirements for a particular barrier by taking into account the fraction of

the work week during which the space beyond the barrier is occupied

Controlled area

the region adjacent to a wall of an x-ray room is used only by occupationally exposed personnel (x-ray wall)

Uncontrolled area

nearby hall or corridor that is frequented by the general public (hallway, bathroom, general public)

Calculating Barrier Shielding Requirements

it is the product of mA-min x U x T must be determined

Primary barrier calculations (What the thickness needs to be)

US shielding is in fractions of lead

1/16th for primary 1.6 mm

1/32 for secondary 0.8 mm

Secondary barrier calculations

Intercepts both scatter and leakage radiation.

Scatter and leakage emerge in all directions, so __

use factor is always 1

Intensity of radiation scattered at a ______ from its source is reduced by a factor of ____ relative to the primary radiation

90 degrees at 1 meter

1000

Leakage regulatory standards mandate that the maximum permissible leakage exposure rate at ____ from the target of a x-ray tube in all directions can not exceed ____ or ____ when it is operated continuously at its maximal permitted kVp and mA combinations

1 meter

100 mR/hr or 0.88 mGya/hr

HVL may be used at barriers to reduce ___

leakage radiation levels to permissible values

Radiation warning signage is important for

safety in radiology departments

Occupancy factor, workload, and use factor must be considered when

calculating thickness requirements for a protective barrier.