Module 4: Radiation Protection

why does protection matter?

ALARA and the patient-benefit balance

How is exposure controlled?

time, distance, shielding

how equipment and room design reduce:

unnecessary dose

Radiation protection is a ____, not a single device

system

protection must address the__

patient, personnel, and the public

Good practice of radiation protection means;

diagnostic information with the least reasonable exposure

health physics deals with:

research, teaching, and operational aspects of radiation safety

health physics includes:

occupational protection and minimizing dose to the population

Health physics developed historically from ____, but is central to modern medical imaging

nuclear work

Health physics

• Two recurring concepts:

ALARA and the linear nonthreshold model (no dose is safe)

ALARA stands for

as low as reasonably achievable

ALARA does not mean no radiation, it means-

no unnecessary radiation

ALARA

• The radiographer controls many ____ choices

practical dose-reduction choices

Cardinal principles of protection

Time, distance, shielding

Time

• Dose is ___ related to exposure time

directly

• double the time, double the dose

Exposure Time formula?

Exposure = exposure rate x time

What can you do to reduce time in fluoro

Use pulsed fluoro, intermittent operation, last-image hold, and 5 minute timer

Time may also affect image ____

quality (motion)

Distance

• Exposure ____ rapidly as distance increases

decreases

• inverse square law

Distance

• In diagnostic imaging, the ___ is often the major source of scatter

patient

Distance

• For the patient distance is ____ 40’’, 72’’ , for technologists its a ____

fixed, variable

Approximate exposure rate, at normal position, at waist height is ____

3 mGy/hr

Shielding

• What are common shielding materials?

lead and concrete

Shielding

• Half-value layer (HVL):

thickness that reduces ingensity to 50%

Shielding

• Tenth-value layer (TVL):

thickness that reduces intensity to 10%

Shielding

• 1 TVL is approximately how many HVLs

3.3 HVLs

Shielding works best when combined with:

time and distance

Occupational Dose Monitoring

• Most Occupational Dose in diagnostic imaging is associated with:

fluoroscopy

Occupational Dose Monitoring

• lead aprons greatly reduce:

trunk dose, nearly zero

Occupational Dose Monitoring

• Effective dose (EfD) estimates:

whole-body risk from partial-body exposure

• weighted average of dose of each organ and tissue

Occupational Dose Monitoring

• Effective dose to entire body is estimated to be ____ of dosimeter reading

10%

Occupational Dose Monitoring

• Example; collar dosimeter recieves 1 mSv, what is the effective dose to whole body?

100 uSv

NCRP Report No. 102 was published ??

published in 1989 by the national council on radiation protection and measurements (NCRP)

NCRP Report No. 102 - what is it?

• Foundational guidance for the design, performance, and safe use of medical radiation equipment

• addresses equipment protection, radiation surveys, personnel monitoring, diagnostic imaging, and pt/staff protection

Built-in protection: The x-ray unit

• ____ housing limits leakage and off-focus radiation

lead-lined tube housing

Built-in protection: The x-ray unit

• leakage radiation measured at a distance of 1 meter from the x-ray source cannot exceed ____ when the tube is operated at its highest voltage at the highest current that allows continuous operation

1 mGy/hr

Built-in protection: The x-ray unit

• control panel is:

located behind a protective barrier with an observation window