Chapter 15 Management of Imaging Personnel Radiation Dose

"The intensity of radiation is inversely proportional to the square of the distance from the source"

Inverse square law (ISL)

Protects against leakage and scatter radiation

secondary protective barrier

Annual occupational effective dose in metric units for whole body exposure during routine operations

50mSv

Restricts the dimensions of the radiographic beam so that it's margins do not extend beyond the image receptor

Positive beam limitations (PBL)

Prevents direct, or unscattered, radiation from reaching personnel or members of the general public on the other side of the barrier

Primary protective barrier

Monthly allowable equivalent dose to the embryo fetus in metric units from occupational exposure of a pregnant radiologist

0.5 mSv

Beam direction factor

Use factor(U)

Annual effective dose limit set for individual members of the general public

1mSv

Specified either in units of mAs per week or milliampere-minutes per week

Workload (W)

During a standard fluoroscopic examination, when the Bucky tray is positioned at the foot end of the table, this device automatically covers the Bucky slot opening in the side of the X-ray table. It protects the radiologist and radiographer at the gonadal level

Bucky slot shielding device

Most common materials used for structural protective barriers

Lead and concrete

This is used to modify the shielding requirement for a particular barrier by taking into account the fraction of the work week during which the space beyond the barrier is occupied

Occupancy factor (T)

Permits the radiologist and assisting radiographer to remain outside the fluoroscopic room at a control console behind a protective barrier while the X-ray beam is on

Remote control fluoroscopic system

Mode of operation in which the exposure rate may significantly exceed the rate used in routine fluoroscopy

High level control

During a fluoroscopic exam, this device should be positioned between the fluoroscopist and the patient to intercept scattered radiation above the tabletop

Protective curtain

A permanent protective barrier for the radiographer that is located in an X-ray room housing stationary radiographic equipment

Control booth barrier

A radiation workers whole body lifetime effective dose in mSv should not exceed 10 times the persons age in years

CumEfD limit

All the radiation that arises from the interaction of an x-ray beam with the atoms of a patient or any other object in the path of the beam

Scatter radiation

Principle that holds that occupational exposure of the radiographer and other occupationally exposed persons should be kept as low as reasonably achieveable

Alara concept

The average annual gonadal equivalent dose to members of the population who are of childbearing age

GSD

Consists of radiation that has been deflected from the primary beam. This radiation is made up of leakage radiation from the tube housing and scatter primarily from the patient

Secondary radiation

Glasses with optically clear lenses that contain a minimal lead equivalent protection level of 0.35 mm

Protective eyeglasses

Should be used to immobilize patients during radiographic exposures whenever possible, instead of people

Mechanical restraining devices

Special garments that are conventionally made of lead-impregnated vinyl and are worn during fluoroscopic and certain radiographic procedures

Protective apparel

A portable device for producing real-time images of a patient. This device holds an X-ray tube at one end and an image intensifier at the other end

C-arm fluoroscope

The purpose of an additional monitor to a pregnant worker is to ensure that the monthly EqD to the embryo fetus does not exceed ___ in metric units

0.5 mSv

What are radiation sources that can be generated in a diagnostic X-ray room

Primary, scatter, and leakage radiation

During C-arm fluoroscopy, the exposure rate caused by scatter near the entrance surface of the patient (the x-ray tube side) _____ the exposure rate caused by scatter near the exit surface of the patient (the image intensifier side).

Exceeds

For high-level-control interventional procedures, the radiographer should verify that which of the following dose reduction features are available and in good working order?

1. High quality, low dose fluoroscopy mode and pulsed beam operation

2. Manual collimation, correct beam filtration, and removable grids

3. Roadmapping, time interval differences, and last image hold mode

All

Which radiation source poses the most significant occupational hazard for the radiographer?

Scattered radiation

During a fluoroscopic exam, which of the following methods and devices reduces the radiographers exposure?

1. Adequate collimation

2. Control of technical exposure factors

3. Use of a cumulative timing device

All

If the peak energy of the diagnostic x-ray beam is 120 kVp, the primary protective barrier generally should consist of at least ________ and extends ________ upward from the floor of the x-ray room when the tube is 1.5 to 2.1 m from the wall in question.

A. 1.6 mm lead, 2.1 m

B. 1.6 mm lead, 6.3 m

C. 0.8 mm lead, 2.1 m

D. 0.8 mm lead, 6.3 m

A

Which radiation source is the control booth barrier NOT intended to intercept in an X-ray room?

Primary radiation

Which device eliminates non-useful low-energy photons from the primary beam?

Aluminum filtration

What is the MOST effective means of protection from radiation normally available to the radiographer?

As much distance as possible

The lead glass window of the control booth barrier in a stationary radiographic installation typically consists of what lead equivalent?

1.5m lead equivalent

The beam direction factor is also known as the:

Use factor

If the intensity of the X-ray is inversely proportional to the square of the distance from the source, how does the intensity of the X-ray beam change when the distance from the source of radiation and a measurement point is quadrupled?

It decreases by a factor of 16 at the new distance

Leakage and scatter radiation are forms of:

Secondary radiation

Diagnostic X-ray installations must be equipped with:

Radiation absorbent barriers

During fluoroscopy which of the following will provide radiation protection for the radiographer and the radiologist?

1. Using appropriate source to skin distance

2. Having a diagnostic type X-ray tube housing

3. Using a remote control fluoroscopic system

All

Floors of radiation rooms except dental installations, doors, walls, and ceilings of radiation rooms exposed routinely to the primary beam are given a use factor of:

1

If a radiographer moves closer to a source of radiation, the radiation exposure to the radiographer:

Increases significantly

A radiographers annual occupational EfD ___ ____ ____ personal medical and natural background radiation exposure

Does not include

Protective lead aprons and shielded barriers function as _____ shields for imaging personnel

Gonadal

The intensity of radiation is _____ proportional to the square of the distance from the source

Inversely

Radiographic and fluoroscopic exposures should ____ be made when room doors are ____

Only; closed

If the peak energy of an X-ray beam is 100kVp, a Pb apron must be equivalent to at least _____mm thickness of lead.

0.25

The ___ protects radiologist and radiographer at the gonadal level

Bucky

For C-arm devices with similar fields of view, the dose rate to personnel located within a meter of the patient is comparable to that in routine fluoroscopy - approximately several ___ __ ___ (____) per hour

Milligray in air (mGya)

The physical configuration of a C-arm fluoroscopic unit ___ the methods the operator can use to ___ protection from scattered radiation

Limits; achieve

From the perspective of increased radiation safety, it is best to ___ the C-arm to place the X-ray tube under the table and the image intensifier over the table

Reverse

Filtration primarily benefits the ____

patient

During a diagnostic x-ray procedure the patient becomes a source of scattered radiation as a consequence of the _____ scattering process

Compton

At a ___ degree angle to the primary X-ray beam at a distance of __m, the scattered X-ray intensity is generally approximately 1/1000 of the intensity of the primary beam

90; 1

The amount of radiation a worker receives at a particular location is ____ proportional to the length of time the individual is exposed to radiation

Directly

In a typical X-ray room, a secondary barrier should overlap the primary barrier by about ____ cm

1.27

After receiving radiation safety counseling, a pregnant rad tech must read and sign a form acknowledging that she has received counseling and understands the practices to be followed to ensure the ____ of the ____ ____

Safety ; embryo-fetus

Primary radiation is also known as ____ radiation

Direct

Accessory protective shielding includes ____, _____, and _____ ____ made of lead impregnated vinyl

Aprons, gloves, and thyroid shields

No one should touch the tube ______ or ___ _____ cables while a radiographic exposure is in progress

Housing; high tension

When high speed image receptor systems are used, smaller radiographic exposure (less milliamperage) is required, which results in fewer X-ray photons being available to produce _____ ___. Because of this reduction in ____ ____, personnel exposure is decreased.

Compton scatter

It is imperative that the EqD to the embryo-fetus from occupational exposure of the mother not exceed the National Council on Radiation Protection and Measurements (NCRP) recommended monthly EDL of ____ ___ or a limit of ____ ___ during the entire pregnancy

0.5mSv or 5.0 mSv

Maternity protective lead aprons consist of ____ __ ___ equivalent over their entire length and width and also have an extra ____ __ ____ equivalent protective panel that rubs transversely across the width of the apron to provide added safety for the embryo-fetus

0.55 mm lead; 1.0 mm lead

When the distance from the X-ray target, a point source of radiation, is doubled, the radiation at the new location spans an area _____ times larger than the original area. However because the same amount of radiation exists to cover this larger area, the intensity at the new distance decreases by a factor of __.

Four; 4

Primary protective barriers are located _____ to the undeflected line of travel of the X-ray beam

Perpendicular

In a typical diagnostic X-ray installation, the secondary barrier consists of ___ __ ____

0.8 mm lead

During general fluoroscopy and X-ray special procedures, a neck and thyroid shield can guard the thyroid area of occupationally exposed people. It should be ___ __ ___ equivalent

0.5 mm lead

Protective lead gloves of at least ____ __ ____ equivalent should be worn whenever the hands must be placed near the fluoroscopic field

0.25 mm lead

For better visualization of small body parts, C-arm fluoroscopes have the capability to _________ the image.

Magnify

During a fluoroscopic examination, a ______ protective apron is recommended to protect personnel who must move around the X-ray room

Wraparound

The radiographer should attempt to stand at ____ _____ (__ degrees) to the patient; when the protective factors of distance and shielding have been accounted for, this is the place where the ____ amount of scattered radiation is received

Right angles ; 90; least

Who should determine the exact requirements for protective structural shielding for a particular imaging facility

A qualified medical physicist

Protective eyeglasses have what lead equivalent protection?

0.35 mm

How does a lead lined, metal, diagnostic-type protective tube housing protect the radiographer and the patient from off-focus, or leakage, radiation?

By restricting the emission of X-rays to the area of the useful or primary beam

What is the annual EqD for localized areas of the skin and hands?

500 mSv