Radiology Lecture 13: Radiation Safety

What is the most common radiation/dose relationship theory?

Linear, non-threshold (LNT)

What does the Linear, non-threshold (LNT) state?

There is no radiation threshold that is safe

What are the two radiation protection goals?

1. Prevent deterministic effects

2. Minimize risk of stochastic effects

What is the average radiation exposure for a person in the US in 1980?

3.1 mSv

How much of the radiation exposed to a person in the US in 1980 is from the background?

83%

How much of the radiation exposed to a person in the US in 1980 is from medical factors?

15%

What is the average radiation exposure for a person in the US in 2006?

6.2 mSv

How much of the radiation exposed to a person in the US in 2006 is from the background?

50%

How much of the radiation exposed to a person in the US in 2006 is from medical factors?

48%

How much of the radiation exposed to a person in the US in 2006 is from radiography?

5%

How much of the radiation exposed to a person in the US in 2006 is from dental factors?

2.5%

What total of population exposure is due to radioraphy?

0.125%

What does ALARA stand for?

As

Low

As

Reasonably

Achievable

What are the three ways to lower radiation exposure for patients?

1. Justify

2. Optimize

3. Limit

What are the five principles of radiation protection?

1. Awareness

2. Avoidance

3. Time

4. Distance

5. Shielding

How many times should x-ray machines be inspected in Maryland?

Once per year

How many times should does the state inspect x-rays?

Once every three years

How much x-ray beam area reduction is done by the collimator?

60 - 70%

How much x-ray beam dose reduction is done by the collimator?

45 - 95%

What does reducing scatter using a collimator improve?

Contrast

Which shape of collimator is routinely used for x-rays?

Rectangular

Which metal filtration absorbs the lowest energy photons?

Aluminum

Which metal filtration is used in CBCT?

Copper

What does filtration in x-rays reduce?

Patient exposure

What is the acceptable operating voltage of intraoral x-rays?

60 - 80 kVp

What is required for the patient to wear during x-rays for protection?

Lead apron

When should thyroid collars not be used?

Panoramic

Which apron is not used for standing panoramic imaging?

Lap apron

Would a 12" or 8" focal spot to receptor distance (SID) be preferred?

12"

What are the two benefits of a longer focal spot to receptor distance (SID)?

1. Reduce skin dose

2. Increased image quality

What should the speed of the imaging receptor exceed?

ANSI speed group

How many feet away from an x-ray behind a barrier should you stand?

6 feet

What angle from the x-ray beam should you stand?

90 - 135

How much lower is x-ray intensity when it is scattered by air compared to the main beam?

0.1%

What two things should an operator never do while taking an x-ray?

1. Hold receptor

2. Hold tube head

How much radiation in the body provides no significant effects?

500 mSv

How can you calculate the maximum accumulated dose (MAD) for a person?

10 mSv x age

How much whole body radiation per year do you get from public exposure?

5 mSv

What is the dose limit for the Embryo-fetus per month after pregnancy is known?

0.5 mSv

Is there a limit for diagnostic radiography?

No

Which personal monitoring device for radiation has a special type of sensitive film in a special holder with metallic filters?

Film Badges

What are the two benefits of film badges?

1. Inexpensive

2. Permanent record

What are the two cons of film badges?

1. Over response at low energies

2. Not good after 1 month

Which personal monitoring device for radiation that uses lithium fluoride crystal and absorbs energy that is read by a special reader?

Thermoluminescent Dosimeter (TLD)

What part of an x-ray must be permanently mounted?

Exposure switch

What are the two functions of the exposure switch?

1. Visually indicates exposure

2. Audibly signals that the exposure has terminated

How many hours of background dose is equivalent to an intraoral image?

6 hours

What is the risk of cancer per exposure for x-rays?

1 in 2,000,000

What is the risk of dying from cancer in the US?

17 - 20%

How can you calculate background equivalent dose in days?

Effective Dose / 8

What is the term for the small chance that a fatality would occur from some activity?

Micromort

How much life is lost by working in a nuclear plant?

51 days

How much life is lost with annual radiation doses?

18 days

How many micromorts does a FOV CBCT scan carry the risk of?

5 micromorts

Is pregnancy a contraindication to diagnostic radiography?

No

Is there a risk of birth defects with a radiation dose of 0 - 50 mGy?

No