Module 5: Radiation Biology & Protection

What is radiation protection?

What is radiation protection?

The physical, technical and procedural factors involved in protecting both patients and personnel from unjustified radiation exposure

Absorbed dose

Amount of energy absorbed per unit mass

______ ________ is responsible for biologic damage

Absorbed dose

How is absorbed dose expressed?

• Grays (GY): Quantified amount of radiant energy transferred to an object

• Previously RAD (radiation absorbed dose)

What is needed for safe operation of x-ray equipment?

• Technique charts

• Positioning aids

• Protective clothing

• Personnel dosimetry

• Quality control

All living cells can be damaged by ________ radiation

Ionizing

Biologic damage can be _______ or _________

somatic, genetic

What is the threshold relationship of biologic effects?

• Point where a response to increasing stimulus first occurs

• Biologic effects observed only when threshold is reached

What is the non-threshold relationship of biologic effects?

• Any radiation dose has potential to produce a biologic effect

• No radiation is believed to be safe

Deterministic (non-stochastic) effects

• Biologic somatic effects of ionizing radiation that can be directly related to the dose received

• Have a threshold

Examples of deterministic effects

• Erythema (skin burn)

• Sterility

• Cataracts

Stochastic (probabilistic) effects

• Probability of occurrence increases with dose

• Regarded as main health risk from low dose radiation from diagnostic exposures

Example of Stochastic effects

Chance of radiation induced leukemia considerably greater after exposure to a dose at 100 than 1 rad, but no difference in severity of disease

What are the fundamental principles of radiation protection

• Net Benefit

• ALARA

• Dose limits

Net benefit

• Benefit vs. risk: Justify radiation exposure

• Medical exposure to radiation should be of some benefit to the individual

ALARA

As Low As Reasonably Achievable

What are dose limits?

• Quantity or amount of radiation exposure that must not be exceeded

• Pertains to doses received by individual on a yearly basis or accumulated over a working lifetime

______ ________ are intended to reduce the probability of biological effects

Dose limits

How are dose limits expressed?

Sieverts (SV)

Cardinal Principles of Radiation Protection

• Minimize time

• Maximize distance

• Maximize shielding

Exposure = ________ ________ x _________ _________

exposure rate, exposure time

As ________ _______ increases, so does ________ _______ received

exposure time, radiation dose

What is the benefit of reducing exposure time on the image quality?

Reduces motion blur

What is the benefit of maximizing distance from the image generator?

Most effective means of protection from ionizing radiation

Inverse square law

Radiation intensity is inversely related to the square of the distance from the source

What substances are used to shield from radiation?

• Lead

• Concrete

Primary protective barrier

Struck by primary or direct radiation

Secondary protective barrier

Provides shielding from scatter radiation and leakage radiation

What type of shielding must exist when producing x-ray images?

• Gonadal shielding

• Personnel shielding

• Room shielding

• X-ray tube shielding

Filtration (Personnel protection techniques)

• Reduces the amount of low energy photons that reach patient

• Reduces scatter

Technical factors (Personnel protection techniques)

• As energy of the beam increases, radiation scatter moving in in foreword direction increases

• Amount of scatter radiation is decreased

High-Speed image receptors (Personnel protection techniques)

• Less mAs required

• Fewer photons available to produce scatter

Correct positioning (Personnel protection techniques)

• Reduces repeat exposures

• Reduces chance for personnel exposure