Introduction to Radiation Protection CHAPTER 9 study flashcards

What is “Radiation?

Radiation refers to kinetic energy that passes from one location to another and can have many manifestations

“many different types of radiation exist”

Ionizing:

x rays, gamma rays, high energy UV (atomic damage potential)

(Has sufficient energy to eject electrons from an atom)

Radiation that produces positively and negatively charged particles (ions)

Non-ionizing:

visible light, infrared, radio waves

(Does not have sufficient kinetic energy to eject electrons from the atom)

* Please note non-ionizing radiation does not mean it is harmless or cannot cause damage

Sources of Ionizing Radiation

Natural Background

earth, cosmic rays

Sources of Ionizing Radiation

Man-Made-

mainly x rays, CT scanning (medical)

Terrestrial Radiation

◦Naturally occurring radioactive materials in the Earth. Uranium, thorium, and radon

Cosmic Radiation

High powered energy from the solar system. Sun and stars

Human Made Ionizing Radiation (X-Rays!)

Form of electromagnetic radiation

• Travels at the speed of light

• X-rays are bundles of energy that move through ‘space’ (from the x-ray tube to the patient)

• Photons

X-Ray Production

Source of electrons

◦Thermionic emission from Cathode filament (mA)

Means for setting them in high-speed motion

◦Potential difference across the X-ray tube (kVp)

Mechanism for decelerating them abruptly

◦Target of the Anode

 All of these conditions are met by the X-ray tube and it’s electrical supply.

3 Fates of X-Ray Photons after Exiting the Tube

1.Penetrate

2.Scatter

3.Absorb

X-Ray Interactions with Matter

• Classic coherent scattering

• Photoelectric interactions

• Compton scattering

• Pair production (Radiation Therapy)

• Photodisintegration (Radiation Therapy)

 

Photoelectric interactions and Compton scattering are particularly important in diagnostic radiography.

Photoelectric Effect

Occurs within the diagnostic X-ray energy range.

 Incoming X-ray photon is completely absorbed by collision with inner-shell electron.

•Responsible for largest contribution to patient exposure

 

Compton Scattering

Occurs within the diagnostic ranges of X-ray energies

• Incoming x-ray photon collides with outer-shell electron of an atom.

• The photon loses some of its energy through collision, scatters off in a random direction (scatter angle), and undergoes other interactions until its energy is totally absorbed.

• Most occupational exposure is from Compton Scatter

Photoelectric Absorption-

X Rays are absorbed in the body

◦Most influential to patient exposure

Compton Scattering-

X Rays scatter and can also affect the image

◦Most influential to occupational exposure

International System of Units) adopted in 1985

Radiation is measured in multiple ways for many different reasons…

Exposure (X)

Measure of ionization in air as a result of exposure to x-rays or gamma rays

Air Kerma

Measures transfer of kinetic energy to tissue or air.

◦Replaces the traditional unit of Exposure(X)

Absorbed Dose (D)

Measures the amount of energy absorbed in any tissue.

◦Measurement depends on:

◦Energy of the x-ray beam

◦Type of the tissue irradiated

Effective Dose (EfD)

Best measure of the overall risk of exposure to humans from ionizing radiation

◦Used for measurement of occupational exposure

Dose Equivalent (EqD)

 

The product of the average dose in a tissue or organ in the body and its associated weighting factor, or quality factor.

 

Standards for Regulation of  Exposure

• Standards are regulated by the FDA and its Center for Devices and Radiological Health (CDRH)

•Receives advice from NCRP (National Council of Radiation Protection& Measurements)

 • Effective dose limit recommendations have been set to minimize the biologic risk to exposed persons

Dose Limits per NCRP
(National Council of Radiation Protection& Measurements)

“Upper boundary doses of ionizing radiation that result in a negligible risk of bodily injury or genetic damage”

50 mSv per year for the worker

Average Person’s Annual Dose (non imaging worker)

1/10th the occupational worker’s annual limit = 5 mSv

Need for Radiation Protection

X-rays are Ionizing.

 

• X-rays have enough energy to cause damage to living cells (atomic).

 

Everyone involved in the medical application of ionizing radiation must have at least a basic knowledge of effective methods/practices to minimize its effects.

Dose – Response Relationship

Physicians use a “risk vs. benefit” rationale when ordering ionizing radiation studies.

•Benefits of an exam must outweigh the potential risks from radiation exposure.

•Doses should be kept as low as possible because no dose is considered totally risk-free.

•ALARA mandates a no-threshold theory of exposure.

Early Effects of Radiation

Large amount of radiation over a short period of time

• Acute Radiation Syndrome (ARS)

•Prodromal Stage

•Latent Stage

•Manifest Stage

•Cell recovery or cell death

• Predictable outcomes; threshold amounts

Radiation Syndromes

Bone marrow syndrome

• Gastrointestinal syndrome

• Central nervous syndrome

 •Amount of dosage to cause these syndromes is far greater than those received by the occupational worker or patient.

 

 

Late Effects of Radiation

Late Effects: can develop over a long period of time after exposure

 

Two types of Late Effects

1 ) Somatic Effects

2 ) Genetic Effects

The more a person is exposed to ionizing radiation, the higher their chance of late effects. Always a potential THREAT; practice radiation protection & safety at all times.

Late Somatic Effects –

in general body cells

◦Non-gonadal areas

◦Effects the individual that was exposed

◦May affect all body cells

◦Two most common are cancer and cataracts

◦Not apparent for many years after irradiation

◦May occur from previous acute high dose OR chronic low dose exposure

◦Non-threshold (any amount of radiation could cause harm)

Late Effects of Radiation cont.

Genetic Effects – reproductive cells

Mutations can occur

◦Effects the exposed individual’s offspring

◦Gonadal organs/components

◦Testicles / sperm

◦Ovaries / eggs

Patient Dose

Absorption of x-ray photons is the biggest contributor to patient dose

Occupational Dose

Primarily from COMPTON SCATTER

ALARA

“As Low As Reasonably Achievable.”

 Using LOWEST radiation exposure that will produce OPTIMALdiagnostic quality radiographs

• FIRST exposure ideal

• Limit/reduce repeat exposures/exams

Repeats = Increased Exposure

Repeats result in at least double the intended exposure

Primary concern because:
NO DOSE level is safe!

               Radiation protection is concerned with:

Physical aspects

◦What body part are we imaging?

◦Reproductive organs and thyroid are more sensitive to radiation

Technical aspects

◦Technical Factors: how much radiation are we exposing the patient to?

Procedural factors involved in protecting patients and personnel

◦Lead aprons and distance from the source

◦Collimation / field size

CARDINAL RULES
of Radiation Protection

1. Time

•  Amount of time in room

•  How long the exposure is

2. Shielding

•  Leaded Protection (walls, glass, aprons, gloves, goggles, etc.)

3. Distance

•  How far from the source the tech or the patient is

•  MOST IMPORTANT

Patient Protection: What can we do?

Low exposure (low mAs and highest possible kVp)

•Reducing the mA (quantity)

•Shortest exposure time (s/ms)

 

• Shielding

 

• Collimation (beam restriction)

 

• Avoid repeats (without compromising quality/safety)

Patient Dose Considerations

Let’s expose the patient to QUALITY

• What technical factor controls penetration power? --kVp

• kVp directly influences the power or quality of the beam.

◦Reducing weak or low quality photons = decreased patient exposure

Post Signs, Ask Questions!

Young, rapidly developing cells are sensitive to ionizing radiation

 

•Be sure to ask patients of childbearing age, if there is a possibility of pregnancy

 

•When in doubt, ask anyway

 

•Don’t assume they read and understood the sign

 

•Reinforce the message

 

•Consent forms (document attestations)

 

•Be the patient advocate for radiation safety

Occupational Protection: What can we do?

Minimize time spent in room when ionizing radiation is being produced

• Maintain the longest distance from the source of exposure

• Shield yourself when applicable (e.g. apron, gloves, goggles, etc.)

• Use appropriate technical factors (reduce scatter)

• Avoid holding patients during exposures

• Employ best practices of radiation safety

Pregnant Student

• Very low risk to fetus if good ALARA practices are followed.

• Dose limit for pregnancy term is 5 mSv.

• Declaration of pregnancy is voluntary.

•Pregnancy announcement can be revoked

• Pregnant student is provided a 2nd dosimetry badge.

•Fetal exposure monitored monthly

•0.5 mSv per month applies during pregnancy

Radiation Monitoring

Any occupational worker who is regularly exposed to ionizing radiation must be monitored to determine estimated exposure.

•Any worker who is likely to receive more than 1/10th the recommended dose-equivalent (5 mSv) limit should be monitored.

• Three popular monitoring devices:

•Direct Ion Storage Dosimeter (DIS)

•Optically stimulated luminescence dosimeter (OSL) most commonly used

•Thermoluminescent dosimeter (TLD)

• Monitors measure the quantity of radiation received on the basis of conditions in which the radiologic and imaging sciences professional was placed.

• Exposure data are collected for a specified period of time. (typically monthly or every 2-3 months)