Radiation Protection

Radiation

Form of energy that travels through space and matter. This energy can move in the form of waves or particles.

1. Cosmic rays

2. Terrestrial radiation

3. Internally deposited radionuclides

4. Radon (largest source)

Radiation from natural sources

Radon

radioactive gas that comes from the decay of uranium in the earth.

It emits alpha particles, which are not penetrating, and therefore

contributes a radiation dose only to the lung

1. Medical

2. Nuclear power generation

3. Research applications

4. Industrial sources

5. Consumer items

Radiation from man-made sources

Radiation protection

tool to protect health against the risks generated by the use of ionizing radiation

1. Justification

2. Optimization

3. Dose Limit

ICRP’s Three Fundamental Principles of Radiation Protection

1. Prevent deterministic effects

2. Reduce stochastic effects

Aims of radiation protection

Intensity or the amount of ionization produced by X-rays or gamma rays in air.

What does exposure measure?

Roentgen (R) - Old unit

Air kerma (Gya) - SI unit

C/kg - Coulombs per kilogram (C/kg) - Special Unit

1 R = 2.58 × 10⁻⁴ C/kg

Units for exposure

Exposure

Common in quality control, calibration, and output measurement of X-ray machine.

Energy absorbed per unit mass of tissue

What does absorbed dose measure?

rad (radiation absorbed dose) - Old unit

Gray (Gyt) – SI unit

J/kg = Joules per kilogram - Special Unit

1 rad = 0.01 Gy

1 Gy = 1 J/kg = 100 rad

Units for absorbed dose

Absorbed dose

Used in estimating how much radiation energy is actually absorbed by the patient or material

Overall biological risk of radiation exposure to the entire body, even if only part of the body is irradiated.

What does effective dose measure?

rem (roentgen equivalent man) - Old unit

Sievert (Sv) – SI unit

J/kg = Joules per kilogram - Special Unit

1 Sv = 100 rem

Units for effective dose

Effective dose

Expressing the quantity of radiation received by radiation workers and populations.

Rate of decay of radioactive atoms per unit time

What does radioactivity measure?

Curie (Ci) - Old unit

Becquerel (Bq) - SI unit

d/s - Disintegration per second - Special unit

1 (Bq) = 1 dps

1 (Ci) = 3.7 x 1010 dps

Units for radioactivity

Radioactivity

Used in nuclear medicine and radiopharmaceuticals

Health physics

Concerned with providing radiation protection and minimizing occupational dose to the public

Health physicist

Radiation scientist concerned with the research, teaching, or operational aspects of radiation safety

1. Design equipment

2. Calculate and construct barriers

3. Develop administrative protocols

Roles of the health physicists

Linear Non-Threshold model,

which addresses the probabilistic risk of cancer, leukemia, and genetic effects even at low radiation doses. Effective implementation requires continuous monitoring of both occupational and patient doses in diagnostic imaging

What model drives the ALARA principle?

1. Time

2. Distance

3. Shielding

Cardinal principles of radiation protection

Directly proportional: when time is doubled, exposure is doubled

Relationship between time and exposure

Exposure = exposure rate x exposure time

Formula for exposure

5-minute reset timer

Reminds the radiologist that a considerable amount of fluoroscopic time has

elapsed. The timer records the amount of x-ray beam on time.

Inversely proportional, computed by the inverse square law

What is the relationship between distance and radiation exposure?

Formula for distance, inverse square law

50 uGya/hr or 5mR/hr

During fluoroscopy, what is the approximate exposure at two steps back?

Because during fluoroscopy, the ptx is an extended source of radiation because of the scattered x-rays generated within the body

Why does the inverse square law not apply to fluoroscopy?

Take two steps back, and take one step to the side and get behind the radiologist

Best step to minimize radiation exposure during fluoroscopy?

Half-value layer (HVL) or

Tenth-value layer (TVL)

The amount that a protective barrier reduces radiation intensity can be estimated if the _____ or _____ of the barrier material is known

One TVL

Is the thickness of absorber that reduces the radiation intensity to one-tenth its original value.

3.3 HVL

1 TVL =

Use of protective apparel

Example of application of shielding in radiology

0.5 mm Pb, equivalent to 2 HVLs, which would reduce occupational exposure to 25%

Lead content of protective aprons and its equivalent, and how much exposure it can reduce

10%

oblique angle

Actual measurements show that such protective aprons reduce exposure to approximately _% because scattered x-rays are incident on the apron at ______ _____.

Protective x-ray tube housing

Every x-ray tube must be contained within protective housing that reduces leakage radiation during use.

100 mR/hr (1 mGya/hr)

1 meter

Leakage radiation must be less than ______ at a distance of _____ from the protective housing.

Control panel

Must indicate the conditions of exposure and must positively indicate when the x-ray tube is energized.

tape measure

A source-to-image receptor distance (SID) indicator must be provided. This can be as simple as a ____ _____ attached to the tube housing, or as advanced as lasers.

2%

The SID indicator must be accurate to within __ of the indicated SID.

Positive Beam Limitation

Automatic, light-localized, variable-aperture collimators automatically adjust the size of the X- ray field to match the size of the image receptor (IR).

Positive Beam Limitation

PBL

2%

The PBL must be accurate to within __ of the SID.

Beam Alignment

In addition to proper collimation, each radiographic tube should be provided with a mechanism to ensure proper alignment of the x-ray beam and the image receptor.

2.5 mm Al

All general purpose diagnostic x-ray beams must have a total filtration (inherent plus added) of at least _____ when operated above 70 kVp.

50 and 70 kVp

Radiographic tubes operated between _____ must have at least 1.5 mm Al.

0.5 mm Al

Below 50 kVp, a minimum of _____ total filtration is required.

Reproducibility

For any given radiographic technique, the output radiation intensity should be constant from one exposure to another.

This is checked by making repeated radiation exposures through the same technique and observing the average variation in radiation intensity.

How is reproducibility checked?

5%

When checking for reproducibility, the variation in x-ray intensity should not exceed ___.

precision radiation dosimeter

three exposures

kVp control

10 exposures

Two methods are available to evaluate exposure reproducibility; both rely on a _____ _____ _____.

First, one can make a series of at least _____ _____ at the same technique factors, having changed technique controls between each exposure. If the result is not reproducible, this is usually the result of error in the ___ _____.

Second, one can select a combination of technique factors and hold them constant for a series of __ _____.

Exposure linearity

The ability of a radiographic unit to produce a constant radiation output for various combinations of mA and exposure time.

10%

The maximum acceptable variation in linearity is ___ from one mA station to an adjacent mA station.

mGya/mAs (mR/mAs)

Radiation intensity is expressed in units of _____.

Operator Shield

It must not be possible to expose an image receptor while the radiologic technologist stands unprotected outside a fixed protective barrier, usually the console booth.

2 meters

The exposure switch of such an imaging system must allow the operator to remain at least __ _____ from the x-ray tube during exposure. The useful beam must be directed away from the radiologic technologist while positioned at this minimum distance.

• 38 cm (15 inches) for stationary fluoroscopic units

• 30 cm (12 inches) for mobile C-arm fluoroscopy

Typical minimum SSD:

• _____ for stationary fluoroscopic units

• _____ for mobile C-arm fluoroscopy

gonadal level

0.25 mm Pb

During fluoroscopy, the Bucky tray is moved to the end of the examination table, leaving an opening in the side of the table approximately 5 cm wide at _____ _____.

This opening should be covered automatically with at least _____ equivalent.

protective curtain

0.25 mm Pb

A _____ _____ or panel of at least _____ equivalent should be positioned between the fluoroscopist and the patient.

cumulative timer

audible signal

A _____ _____ that produces an _____ _____ when the fluoroscopic time has exceeded 5 minutes must be provided.

Dose Are Product (DAP)

measure of the total amount of radiation delivered to the patient

DAP = Radiation dose × Area of the x-ray beam

Formula for DAP

Unit: Gy·cm² (gray × square centimeter)

Unit for DAP

DAP

may be used to monitor radiation output from radiographic and fluoroscopic imaging systems

placed near the x- ray source below the collimator, before the beam enters the patient

Where are DAP meters placed?

… dividing the DAP measurement by the area of the beam at the skin.

The risk for injury to the skin where the beam enters the patient can be derived by …

21 mGya/min (2.1 R/min)

80 kVp

Note:

The intensity of the x-ray beam at the tabletop of a fluoroscope should not exceed _____ for each mA of operation at _____.

100 mGya/min (10 R/min)

200 mGya/min (20 R/min)

If there is no optional high-level control, the intensity must not exceed _____ during fluoroscopy.

If an optional high-level control is provided, the maximum tabletop intensity allowed is _____.

effective radiation dose (E)

The overall stochastic risk to a patient depends on _____ _____ ____, which is related to tissue radiation dose and to the volume of tissue exposed.

Tissue Radiation Dose

Refers to the energy deposited locally

Tissue Radiation Dose

The quantity that best reflects the potential for injury to that tissue (deterministic effect)

If the radiology facility is located on an upper floor

In area survey, when is it necessary to shield floors of radiology rooms as well?

1. Primary radiation

2. Secondary Radiation

   a. Scatter radiation

   b. Leakage radiation

Three types of radiation considered when constructing the protective barrier

Primary Radiation

The most intense radiation and therefore the most hazardous and the most difficult to shield

Scatter radiation

Results when the useful beam intercepts any object, causing some x-rays to be scattered

ptx

During radiography and fluoroscopy, the _____ is the single most important scattering object.

0.1%

The intensity of scatter radiation 1 meter from the patient is approximately ___ of the intensity of the useful beam at the patient.

Leakage radiation

Radiation emitted from the x-ray tube housing in all directions other than that of the useful beam.

1 mGya/hr (100 mR/hr)

If the x-ray tube housing is designed properly, the leakage radiation will never exceed the regulatory limit of _____ at 1m.

Primary protective barrier

designated to the wall to which the useful beam can be directed, and shields from primary radiation

Lead bonded to sheet rock or wood paneling specified for architects and contractors in units of pounds per square foot (lb/ft2 )

Used most often as a primary protective barrier

Concrete, concrete block, or brick

1/16 inch of lead

7 ft high

Primary protective barrier

• _____, _____, or _____ may be used instead of lead.

• As a rule of thumb, 4 inches of masonry is equivalent to _____.

• Radiation protection guidelines have established that primary radiation barriers must be _____.

0.4 mm Pb

conventional gypsum board, glass, or lead acrylic

Often, lead is not required for secondary protective barriers because the computation usually results in less than _____. In such cases, _____ _____, _____, ____ _____ is adequate.

1. Distance

2. Occupancy

3. Control

4. Workload

5. Use factor

6. kVp

Factors that affect barrier thickness

source of radiation and the barrier

The thickness of a barrier naturally depends on the distance between the _____ of radiation and the _____. A wall along which an x-ray imaging system is positioned probably requires more shielding than the other walls of the room

Occupancy

time of occupancy factor (T)

If the area were a rarely occupied closet or storeroom, the required shielding would be less than if it were an office or laboratory that was occupied 40 hours per week.

• This concept reflects the _____.

Controlled area

An area that is occupied primarily by radiology personnel andpatients.

recommended occupational dose limit

less than 1 mSv/wk (100 mrem per week)

The design limits for a controlled area are based on the _____ _____ ____ _____; therefore, the barrier is required to reduce the exposure to a worker in the area to _____.

Uncontrolled area

An area that can be occupied by anyone.

1 mSv/ yr (100 mrem/yr)

20 µSv/wk (2 mrem/wk)

25 µSv (2.5 mrem)

Uncontrolled area:

The maximum exposure rate allowed is based on the recommended dose limit for the public of _____.

• This is equivalent to _____, which is the design limit for an uncontrolled area.

• Furthermore, the protective barrier should ensure that no individual will receive more than _____ in any single hour.

level of radiation activity

workload (W)

units of milliampere minutes per week (mAmin/wk)

The shielding required for an x-ray examination room depends on the _____ of _____ _____ in that room.

• The greater the number of examinations performed each week, the thicker the shielding that is required.

• This characteristic is called _____ and is expressed in _____.

Use Factor

Represents the fraction or percentage of time a specific barrier (like a wall, floor, or ceiling) is directly hit by the primary X-ray beam.

Walls: 1/4
Floor: 1

The NCRP recommends that walls be assigned a use factor of ___ and the floor a use factor of _.

1

secondary radiation barriers

A room designed strictly for chest radiography has one wall with a use factor of _. All others have a use factor of zero for primary radiation and thus would be considered ____ _____ _____.

⬆ use factor = ⬆ shielding

⬇ use factor = ⬇ shielding

⬆ use factor = ___ shielding

⬇ use factor = ___ shielding

kVp

penetrability

150 kVp

75 kVp

100 kVp

30 kVp

For protective barrier calculations, ___ is used as the measure of _____.

• Most modern x-ray imaging systems are designed to operate at up to _____. Most examinations, however, are conducted at an average of _____.

_____ for general radiography, _____ for mammography

75 kVp

The average kVp is usually closer to _____ than to 100 kVp.