CLRS 232 Exam 4

Definition of Dose Limits

Describes occupational limits of radiation exposure (replaced MPD)

Know legal dose limits in the United States

Annual: 50 mSv/yr (5000 mrem/yr)

Lens of Eye: 150 mSv/yr (15 rem/yr)

Other Organs: 500 mSv/yr (50 rem/yr)

Cumulative Whole Body: 10 mSv/yr x age

Pregnancy, Entire: 5 mSv (500 mrem)

Pregnancy, Monthly: 0.5 mSv (50 mrem)

Definition of use factor

The amount of time the beam is aimed at a barrier

Definition of workload

A measure of radiation output in one week

Definition of occupancy factor

The amount of time the bordering rooms will be occupied

Protective apparel/what thickness is the requirement

Lead aprons with at least 0.25 mm Pb but 0.5 mm Pb commonly used, must be worn to be effective, gloves available as well

What procedures have the highest occupational exposure?

Fluoroscopy and mobile radiography

Primary barrier and Secondary barrier

Primary: Any wall to which the useful beam can be directed (primary radiation), made of lead and concrete

Secondary: Designed to shield areas from secondary radiation, always less thick than primary (leakage and scatter radiation), made of steel, glass, gypsum, and wood

Difference between primary radiation, leakage radiation, and scatter radiation

Primary: Useful beam

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

Scatter: Results when useful beam intercepts any object causing some x-rays to be compton scattered

Know how to calculate cumulative whole-body dose?

10 mSv x age or 1 rem x age

Where can you wear your occupational radiation monitoring device?

Front at waist or chest level

What does the effective dose take into account?

The relative sensitivity of tissues and organs that absorb dose

What is the purpose of having a dead man exposure switch in a fluoroscopic procedure?

If the operator drops dead or just release the pressure on either the hand or the foot switch, the exposure would be terminated

What is considered an unnecessary examination?

Mass screening for tuberculosis, hospital admission, pre-employment physicals, periodic health examinations, emergency department CT, whole-body multislice helical CT screening, repeat exams, anything where the harm outweighs the benefits

When designing barriers for a radiography suite what must be considered?

Workload, use factor, delivered dose per week and distance from source to barrier and time the space is occupied

What must be considered when you are pregnant and a radiographer?

Lower recommended dose limit (0.5 mSv/month), 2nd dosimeter worn at waist level, termination/involuntary leave of absence may not occur as consequence

What's the purpose of the protective housing of the x-ray tube?

Reduces leakage radiation during use

What is the main source of radiation exposure to radiography staff come from?

Scatter radiation

What is TLD made up of (what material)? And how long can it store information?

Made of lithium fluoride, can measure exposure as low as 50uGya, can be worn for intervals for up to 1 year

Our legal dose limits are based on what type of dose-response relationship?

Linear, non-threshold dose-response relationship

Tissue weighting factor and radiosensitivity

The higher the weighing factor, the more radiosensitive the tissue is

Source to receptor distance has to be within what percentage in radiography

2%

Definition of effective dose

Organ sensitivity to radiation, its for radiation protection purposes, identifies biological effectiveness of radiation energy that has been absorbed, shows long term effects

Occupational dose limit for the lens of the eye?

150 mSv/yr (15 rem/yr)

What is radiation therapy?

A therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator

Why is the ceiling for radiation therapy rooms have just as much shielding as the other walls?

To protect people from the highest level of radiation the machine can produce

What happens to patient entrance skin exposure when the fluoro x-ray tube is too close to the tabletop?

It highly increases

The Geiger-Muller counter is often used for the detection of what?

Radiation contamination

What are the two types of personal monitoring devices?

Thermoluminescent dosimeters (TLD) and optically stimulated luminescence dosimeters (OSL)

Proportional Counters what does it measure?

Measure low intensity radiation, discriminate between alpha and beta particles

Why is the exposure of patients to medical x-rays getting more attention in our society?

1. the frequency of x-ray examination is increasing in all age groups

2. concern among public health officials and radiation scientists is increasing regarding the risk that is associated with medical x-ray exposure

What is Appropriateness Criteria?

Evidence-based guidelines to assist referring physicians in making the most appropriate imaging decision for a specific clinical condition