RAD 205 Test 4

Definition of equivalent dose limits?

A dose that is not expected to produce significant effects

Publication that recommends limits to exposure to ionizing radiation

NCRP Report #116

Which of the following relates to the equivalent dose limits for a non-radiation worker

1/10 that of a radiation worker

Radiation protection standards organizations

-ICRP (international commission on radiological protection)

-NCRP (national council on radiation protection and measurement)

-UNSCEAR (United Nations scientific committee on the effects of atomic radiation)

-NAS/NRC-BEIR (national Academy of sciences/national research council committee on the biological effects of ionizing radiation)

Radiation protection standard organizations are responsible for what?

Evaluating the relationship between radiation dose and induced biologic effects

Formulating risk estimates of somatic and genetic effects after irradiation

Regulatory agencies are responsible for

Enforcement of the established standards

Protecting the general public patients and occupational radiation workers through enforcement of protection standards

Regulatory agencies

-FDA (food and drug administration)

-NRC (nuclear regulatory commission)

-EPA (environmental protection agency)

-OSHA (occupational safety

and health administration)

Which agencies: research evaluate and recommend?

NCRP

ICRP

NAS / NRC-BEIR

Which organizations enforce standards?

FDA

NRC

EPA

Agreement states

Agreement states

Most states have agreements with NRC to assume responsibility of enforcing radiation regulations through their own state health departments

Protection philosophy

-ALARA

-guidelines based on linear non-threshold DRR

-benefits should outweigh risks

Dose Limits (DL) have been established for

occupationally exposed personnel, as well as members of the general public

The dose limit, if received annually, the risk of death would be

1 in 1000, which is similar to other low risk occupations

Effective Dose Limit (E) or (EfD) used for

Whole body exposure

Equivalent Dose Limit (EqD) used for

Partial body exposure

Effective dose

Provides a measure of the overall risk of exposure to ionizing radiation

Incorporates radiation type and tissue radio sensitivity by using weighting factors

Effective dose formula

EfD= D x Wr x Wt

D-absorbed tissue dose in rads

Wr-Radiation weighting factor

Wt-tissue weighting factor

Gonads Wt vs bone marrow

0.20 gonads

.12 bone marrow

Equivalent dose

Provides a measure of the exposure to partial body tissues based on the type of radiation received

Equivalent dose formula

EqD = D x Wr

D- dose absorbed in rads

Wr- radiation weighting factor

Annual whole body effective dose limit (maximum)

50 mSv per year

Annual whole body effective dose limit (lifetime cumulative)

10 mSv x Age in years

Once total mSv equals 10x age in years, how many mSv are allowed per year?

Only 10 mSv

A 35 y/o technologists lifetime cumulative dose should not exceed _ mSv

350 mSv

Annual Dose Equivalent Limit for Lens of the Eye

150 mSv

Annual dose equivalent limit for tissue and organs (besides the eyes)

500 mSv

(Includes:

Redbone marrow

Breast

Lung and thyroid

Gonad

Skin

All extremities )

Who is the preferred demographic for emergency occupational exposure?

Older volunteers with low lifetime dose

Annual dose equivalent limit for life savings events (skin)

5000 mSv

Effective dose limit for lifesaving events (whole body)

500 mSv to whole body

Effective dose limit for non-lifesaving events (whole body)

"Should" not exceed cumulative lifetime limit

As dose approaches _ in life-saving events, the worker must be informed of acute effects, and long-term increased risk for cancer

500 mSv

Equivalent Dose limits for embryo

Entire gestational period: 5 mSv

Monthly: .5 mSv

Effective Dose limit for education/under 18

1 mSv annual

Equivalent dose limit for education and training: lens of the eye

15 mSv annual

Equivalent dose limit for education and training: skin and extremities

50 mSv annual

Effective dose limit for general public: frequent exposure

1 mSv (whole body)

Effective dose limit for general public: infrequent exposure

5 mSv (whole body)

Equivalent dose limit for general public: lens of the eye

15 mSv

Equivalent dose limit for general public: skin and extremities

50 mSv

NID

negligible individual dose

A risk that can be dismissed

.01 mSv

T/F: Below the level of .01 mSv annual dose (NID), it is not useful to try to limit exposure further

True

Categories of radiation induced somatic effects

Stochastic effects (probablistic effects)

Deterministic effects

Stochastic/probablistic effects are _ likely as dose increases

More

Stochastic/probablistic effects

Increase of incidence (not severity) with increase of dose

Non threshold and random

All or none response

Stochastic effects examples

Cancer

Leukemia

Generic effects

Deterministic effects

Increase in severity as dose increases

Require considerably larger doses

Threshold in nature

Deterministic effects examples

Erythema

Decrease in sperm or blood counts

Cataracts

Epilation

T/F: Virginia is an agreement state

True

The department of health regulates the radiation protection guidelines in Virginia

Dose limits have been established only as _ _ of radiation doses

Upper limits

3 cardinal principles

Time, distance, shielding

The radiation dose to the individual is _ related to the duration of the fluoroscopic or OR study

Directly

If exam time doubles, patient/tech exposure will

Double

The cardinal principle of time should not be confused with

Exposure time and MA stations

An area of radiation protection that is not directly controlled by the radiologic technologist is

Time of exposure during fluoroscopy

Control of time during fluoroscopy mostly lies in the hands of

Radiologists

intermittent fluoroscopy

Practiced by radiation conscious radiologists (fluoro on/off fashion)

5 minute timer

Should always be set prior to fluoroscopic studies to remind radiologist of time elapsed

How can a technologist control the time in fluoroscopy?

Technologist can control the number of times they have to repeat films

As the distance from the radiation source increases, the radiation intensity

Decreases in inverse proportions to the square of the distance

Just taking a few few steps back during fluoroscopy will do what for the technologist?

Increase the distance and drastically reduce exposure

If distance from radiation source is doubled,

intensity is reduced to 1/4 of its original value

If distance from radiation source is increased 3 times

Intensity is reduced to 1/9 of its original value (3 squared = 9)

If distance from radiation source is increased times 4,

Intensity is reduced to 1/16 of its original original value ( 4 squared = 16 )

If the exposure rate from a source is 9000 mR/hr, what is the rate at 3 steps from the source?

1000 mR/hr

What serves is the main source of scattered radiation during fluoroscopy?

The patient

Leakage is

Radiation from the tube that does not hit the target

Scatter radiation

Represents extended (patient) source versus a point source (tube)

Lead

Place between the radiation source and the technologist

High atomic number

Lead absorbs radiation through the

Photoelectric effect

(high binding energy electrons cause x-ray photons to expend all its energy during collision and cease to exist)

Amount of shielding needed to reduce exposure is expressed as

Half value layer

Technologist position during fluoro

If you must stay in the room to observe, after two steps back from the radiation source, take one step to the side and get behind the radiologist.

This move results in additional shielding and the exposure at that position will be zero

Half value layer

The thickness of absorbing material necessary to reduce the radiation intensity to 1/2 of its original value

HVL (half value layer) is usually expressed in

Mm (milimeters) of aluminum

HVL (half value layer) is the only true indicator of

X ray beam quality

As kVp increases, HVL _

Increases

Tenth Value Layer (TVL)

Thickness needed to attenuate 9/10 of the beam

Aluminum makes the beam

Harder (more high quality) by absorbing low energy photons

Original exposure= 300 mGya, how much aluminum is required to reduce intensity of the beam to ~9 mGya if HVL is .2 mm Al

5 HVL x .2 = 1 mm Al to reduce the x ray exposure to 9 mGya

What makes lead an excellent protective barrier?

High density

High atomic number

High absorption coefficient

If an exposure of 16 mR is recorded at 1 m what would the exposure be at 4 m?

1 mR

Protective features required on all equipment

Protective tube housing

Control panel exposure indicator

Filtration

Protective tube housing metal lining- lead minimum

Minimum 1.5 mm lead

Protective tube housing purpose

Protect against:

Electric shock

Leakage radiation

Leakage from protective tube housing must not exceed

1 mGya/hour at 1 meter distance

How does aluminum filtration reduce patient exposure?

Increases beam quality

Decreases beam quantity (intensity)

Decreases unnecessary skin dose

Filtration is expressed in

mm of Al equivalent

3 types of filtration

inherent, added, total

Control panel exposure indicator

Indicator that signals when exposure has been made

Fluoro exposure indicator requirements

KVP and MA meters required

Radiographic exposure indicator requirements

MA meter required

Sometimes an audible beep in addition

Sometimes a light flash in addition

Inherent filtration

Built-in the equipment

Inherent filtration examples

Glass window of x-ray tube

Insulating oil around tube

Inherent filtration must equal

.5 mm Al

T/F: Inherent filtration increases as the tube ages

True

Tungsten plates out on inside of tube starts to stick to window

Which absorbs more radiation

Added filtration

Aluminum sheets inserted between tube and collimator box

Added filtration examples

Light reflecting mirror

Plastic cross hairpiece

Fluoroscopic table top

Patient cradle

Added filtration must equal

1 mm Al

Total filtration

inherent filtration + added filtration

Quality of the beam is _ by filtration, quantity of the beam is _ by filtration

Quality is increased

Quantity is decreased

Total filtration below 50 KVP

.5 mm Al equiv.