Radiation Protection Principles
What are the three cardinal principles of radiation protection?
Time, Distance, Shielding
What is the most commonly used material for shielding in diagnostic radiology?
Lead
SID indicators must be accurate within what percentage?
2%
What is the minimum distance a technologist should stand from a portable x-ray tube?
6 ft or 2 m
What is the primary goal of health physics?
To protect people from radiation hazards
What is the cardinal principle that should be reduced when using fluoroscopy?
Time
What is a half-value layer (HVL)?
The thickness of material required to reduce intensity by 50%
What is the percentage that collimator light and x-ray field alignment need to be within of the SID?
2%
What is the maximum tabletop exposure rate in fluoroscopy without high-level control?
100 mGy/min
What is barrier thickness most influenced by when creating radiography rooms?
Distance to adjacent occupied areas
According to this law, exposure decreases when the distance from a radiation source increases.
Inverse square law
How much lead in an apron is needed to reduce exposure to approximately 1%?
0.5 mm
What is the minimum filtration needed for x-ray tubes that operate above 70 kVp?
2.5 mm Al
What is the minimum source-to-skin distance for stationary fluoroscopy?
38 cm
What is the weekly design limit for an uncontrolled area?
20 µSv/week
When the patient acts as a source of scatter, what kind of source has been created?
Extended area source
What is effective dose?
The dose that accounts for tissue radiosensitivity and overall risk
What is the variation limit for radiographic reproducibility?
±5%
What is the lead equivalence of the fluoroscopic image receptor assembly?
0.5 mm Pb
Which detector is preferred for accurate radiation intensity measurement?
Ionization chamber
Time, distance, and shielding have what kind of effects?
Multiplicative
What is the maximum leakage radiation allowed from an x-ray tube housing?
1 mGy/hr at 1 m
What does linearity testing ensure is proportional?
mAs output
What happens after 5 minutes of fluoro?
An audible signal from the cumulative fluoroscopy timer goes off and needs to be reset
Why does distance still reduce exposure during fluoroscopy despite the patient giving off scatter?
Because extended radiation sources behave like point sources when the distance is sufficiently increased.