Radiation Safety Final Exam

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Radiation

Energy that travels through space or matter as waves or particles.

Ionizing Radiation

Any type of radiation that is capable of removing an orbital electron from the atom

ALARA

“As Low As Reasonably Achievable”  keeping radiation exposure as low as possible.

Inverse Square Law

As distance increases, radiation intensity decreases.

Principles of radiation protection

• Time: Direct Relationship

• Distance: Indirect Relationship

• Shielding: Indirect Relationship

  • 0.25 mm Pb minimum

Time and radiation protection are _______ly related

Direct

Distance and radiation protection are _______ly related

Indirect

Shielding and radiation protection are _______ly related

Indirect

4 special quantities to measure radiation

1. Air KERMA (Kinetic Energy per unit Mass: Gya

2. Absorbed Dose: Gyt

3. Effective Dose: Sv

4. Radioactivity: Becquerel (Bq)

What does KERMA stand for?

Kinetic Energy per unit Mass

4 radiation measurement quantities - What does the absorbed dose express?

Tells us how much radiation doses is absorbed in the patient and tells us short-term effects such as skin erythema and hair loss but not long-term effects

Gyt

4 radiation measurement quantities - What does the effective dose express?

Express long-term effects-used to express the quantity of radiation received by radiation workers and populations

Sv

4 radiation measurement quantities - What does radioactivity express?

Spontaneous release of energy from an unstable atom to get to a more stable state

Bq (Becquerel)

4 radiation measurement quantities - What does Air KERMA express?

Exposure: kinetic energy released per unit mass-measure total energy of ions in air

Gya

Exposure relationship

• More time = more exposure

• More distance = less exposure.

When were X-rays discovered?

November 8th, 1895: Wilhelm Conrad Rontgen in Germany

HVL

Half-value layer; thickness of material needed to reduce beam intensity by half.

Largest natural radiation source

Radon Gas

Others:

• Cosmic Rays

• Terrestrial Radiation

• Internally Deposited Radionucleotides

Human-made:

• X-ray/CT

• Nuclear medicine

• Interventional fluoroscopy

• Conventional radiography/fluoroscopy

Radiation can be…

1. Absorbed

2. Reflected

3. Scattered

4. Refracted

5. Transmitted

Radiation Actions - Absorbed

Energy is retained by a substance (create x-rays)

Radiation Actions - Reflected

The surface returns a portion of the energy (sun)

Radiation Actions - Scattered

The electromagnetic waves are changed from propagating in one direction to all directions (goes where it shouldn’t, which can negatively impact images)

Radiation Actions - Refracted

The electromagnetic waves are changed from propagating in one direction to another direction

Radiation Actions - Transmitted

Energy passes through space or the media

X-ray tube parts

Cathode, anode, filament, focusing cup, target, rotor, stator, glass envelope, tube housing.

Positive/negative sides

1. Cathode = negative side.

   • Filament - coil of wire approximately 2mm in diameter and 1 or 2 cm long

     • Dental imaging systems, portable imaging systems

   • Focusing cup - metal shroud that surrounds the filament

2. Anode = positive side. 2 types

   • Stationary - high tube current and power are not required

   • Rotating - capable of producing high-intensity x-ray beams in a short time

Positive/negative sides - What are the 2 types of anodes?

1. Stationary - high tube current and power are not required

2. Rotating - capable of producing high-intensity x-ray beams in a short time

Why does x-ray tube failure occur?

1. Anode being at high temperatures for a long period of time

2. Filament breaks and becomes thin because of excessive heat

3. The enormous amount of heat that is not dissipated

   1. Radiation - transfer of heat by the emission of infrared radiation

   2. Conduction - transfer of heat from one area to another

   3. Convection - transfer of heat by the movement of a heated substance from one place to another

4. Tube interactions

   1. Heat 99%

   2. X-rays 1%

Tube Failure - Conduction

Transfer of heat from one area to another

Tube Failure - Convection

Transfer of heat by the movement of a heated substance from one place to another

Two types of x-rays generated

1. Characteristic radiation

2. Bremsstrahlung radiation

Characteristic radiation

1. X-rays are produced when outer-shell electrons fill an inner-shell

   1. Projectile electrons interact with inner shell electron

   2. Projectile electron has energy high enough to totally remove an inner-shell electron of the target atom

Bremsstrahlung radiation

• X-rays produced when fast electrons slow down near the nucleus.

• Braking radiation

X-ray interaction with matter

The higher the energy of the x-ray, the shorter the wavelength

• Low energy x-rays interact with whole atoms

• Moderate energy x-rays interact with electrons

• High energy x-rays interact with the nuclei

X-ray interaction with matter - Low energy interacts with…

Whole Atoms

X-ray interaction with matter - Moderate energy interacts with…

Electrons

X-ray interaction with matter - High energy interacts with…

Nuclei

Where are X-rays produced? Gamma rays?

1. X-rays = outside the nucleus/electron cloud.

2. Gamma rays = inside the nucleus.

Radiopaque vs radiolucent

1. Radiopaque = white/light on image such as bone

2. Radiolucent = dark/black on image such as fluid

Pair production

Photon interacts near nucleus and creates a positron and electron

Photodisintegration

High-energy photon hits nucleus and ejects nuclear particles.

Photoelectric effect

Photon is absorbed and ejects an inner-shell electron.

Coherent/classical scattering

Low-energy photon changes direction without ionization

Compton effect

Occurs when x-rays throughout the diagnostic range can undergo an interaction with outer-shell electrons that not only scatters the x-ray but reduces the x-ray and ionizes the atom as well

Most radiation-sensitive cell cycle phase

M phase, also late G2

Low LET radiation

X-rays and gamma rays

Most radiosensitive cells

Blood-forming cells, reproductive cells, and immature rapidly dividing cells

Linear/nonlinear response

1. Linear = damage increases directly with dose.

2. Nonlinear = damage does not increase evenly with dose.

Target molecule

DNA.

LD50/60

Dose that kills 50% of exposed people within 60 days

Tissue weighting factor

Measures how sensitive an organ/tissue is to radiation risk

Radiation weighting factor

Compares biological damage from different radiation types

RBE and LET of X-rays

X-rays have low LET and an RBE of 1

Acute radiation syndromes

1. Hematologic: 1–10 Gy, affects bone marrow, infection, bleeding.

2. GI: 10–50 Gy, nausea, vomiting, diarrhea, dehydration.

3. CNS: 50+ Gy, confusion, seizures, coma, death.

Acute radiation syndromes - Hematologic

1–10 Gy, affects bone marrow, infection, bleeding.

Acute radiation syndromes - GI

10–50 Gy, nausea, vomiting, diarrhea, dehydration.

Acute radiation syndromes - CNS

50+ Gy, confusion, seizures, coma, death.

Dose Limits (5)

1. Occupational whole body: 50 mSv/year or 5 rem/year.

2. Public: 0.1 rem/year or 1 mSv/year.

3. Lens: 150 mSv/year or 15 rem/year

4. Skin/extremities: 500 mSv/year or 50 rem/year.

5. Fetus: 0.5 mSv per month// 5 mSV per whole preganancy (0.5 rem)

Dose limits - Occupational whole body

5 rem/year

Dose limits - Public

0.1 rem/year or 1 mSv/year

Dose limits - Lens

15 rem/year

Dose limits - Skin/extremities

50 rem/year

Dose limits - Fetus

0.5 rem total pregnancy

RBE Formula

Conversions:

• 1 Gy = 100 cGy.

• 1000 mrem = 1 rem.

• 100 rad = 1 Gy.

• 1 rad = 0.01 Gy.

Conversions - 1 Gy = __ cGy

100 cGy

Conversions - 1000 mrem = __ rem

1 rem

Conversions - 100 rad = __ Gy

1 Gy

Conversions - 1 rad = __ Gy

0.01 Gy

X-ray production

About 99% heat and 1% X-rays.

Largest man-made radiation source

Medical imaging, especially CT

Public dose limit

1 mSv/year or 0.1 rem/year

Cumulative effective dose

Age × 10 mSv

Radiation therapy

Use of radiation to treat cancer or abnormal tissue

Controlled vs uncontrolled area

1. Controlled area = radiation workers have safety rules and monitoring.

2. Uncontrolled area = general public area

Deterministic vs stochastic

1. Deterministic = has threshold; severity increases with dose.

2. Stochastic = no threshold; chance increases with dose.

Cell survival

Ability of cells to survive after radiation exposure

Oxygen enhancement ratio

Radiation is more damaging when oxygen is present

Relative biological effectiveness

Compares damage caused by different radiation types

Fractionation/protraction

Gives normal tissue time to repair while still damaging cancer cells

Radiobiology

Study of effects of radiation on living tissue

Radiosensitizer

Substance that makes cells more sensitive to radiation

Radiosensitivity depends on

Cell division rate, cell maturity, oxygen level, and tissue type

Manifest illness

Stage of radiation sickness when symptoms appear

What is Acute radiation syndrome

Illness caused by high whole-body radiation dose over a short time

What is Mean survival time

Average time a person survives after a lethal radiation dose

What is HVL

Amount of shielding needed to reduce radiation intensity by 50%

Target theory

Theory that a cell will die if target molecules are inactivated as a result of radiation exposure