Radiation Protection

Radiation Protection Considerations

I. Ionizing Effects of X-Radiation

A. Electromagnetic Radiation

Electromagnetic radiation consists of wave-like fluctuations of electric and magnetic fields that travel through space at the speed of light (3 × 10⁸ m/s).

Examples of electromagnetic radiation include:

• Radio waves

• Microwaves

• Infrared radiation

• Visible light

• Ultraviolet radiation

• X-rays

• Gamma rays

These radiations differ mainly in wavelength, frequency, and energy.

Wavelength

Wavelength is the distance between two consecutive wave crests.

Frequency

Frequency refers to the number of cycles per second, measured in Hertz (Hz).

Relationship of Wavelength, Frequency, and Energy

These three quantities are related as follows:

• Wavelength and frequency are inversely related

• Energy increases as frequency increases

• Energy decreases as wavelength increases

Formula:

Speed of light = Frequency × Wavelength
c = fλ

Radiations with short wavelength and high frequency have higher energy.

Ionizing Radiation

Ionizing radiation has sufficient energy to remove electrons from atoms, creating positive and negative ions.

Examples of ionizing radiation include:

• X-rays

• Gamma rays

Ionization can cause chemical and biological damage to tissues.

Diagnostic X-rays have extremely short wavelengths ranging from:

10⁻⁸ to 10⁻¹² meters

The unit previously used for very small wavelengths is the Angstrom (Å).

1 Å = 10⁻¹⁰ meters

Sources of Radiation Exposure

Humans are continuously exposed to radiation from two major sources.

Natural Background Radiation

Natural radiation comes from:

• Cosmic radiation from the sun

• Radioactive materials in the Earth’s crust

• Radon gas in the air

• Radioactive materials in food and water

Natural background radiation accounts for the largest portion of human radiation exposure.

Artificial (Man-Made) Radiation

Man-made radiation sources include:

• Medical and dental x-rays

• Nuclear testing fallout

• Nuclear power plants

• Occupational radiation exposure

Among artificial sources, medical radiation contributes the largest exposure.

II. Production of X-Rays at the Tungsten Target

Diagnostic x-rays are produced inside the x-ray tube when high-speed electrons strike the tungsten anode target.

Process:

1. Electrons are produced at the heated cathode filament.

2. A high voltage (kilovoltage) accelerates electrons toward the anode focal spot.

3. When electrons strike the tungsten target, their kinetic energy is converted to X-ray photons.

Two types of X-rays are produced.

1. Bremsstrahlung Radiation

Bremsstrahlung means “braking radiation.”

This occurs when a high-speed electron is deflected by the positively charged nucleus of a tungsten atom.

The loss of energy from the electron is emitted as an x-ray photon.

Characteristics:

• Produces a continuous spectrum of x-ray energies

• Accounts for 70–90% of the x-ray beam

• Produces a polyenergetic beam

2. Characteristic Radiation

Characteristic radiation occurs when a high-energy electron ejects an inner-shell electron (usually K-shell) from a tungsten atom.

Steps:

1. An incoming electron ejects a K-shell electron.

2. A vacancy is created.

3. An outer-shell electron drops down to fill the vacancy.

4. The energy difference is released as a characteristic x-ray photon.

Characteristics:

• Energy is specific to the target material

• Tungsten K-characteristic x-rays ≈ 69 keV

• Represents 10–30% of the x-ray beam

III. Interaction of X-Ray Photons with Matter

As X-rays pass through tissue, their intensity decreases. This process is called attenuation.

Attenuation occurs mainly through two interactions:

1. Photoelectric Effect

In the photoelectric effect:

• A low-energy X-ray photon interacts with tissue.

• The photon completely transfers its energy to an inner-shell electron.

• The electron is ejected from the atom.

This creates a vacancy, which is filled by an outer-shell electron, producing characteristic radiation.

Characteristics:

• Occurs more often in high atomic number materials (e.g., bone, contrast media)

• Increases patient radiation dose

• Produces short-scale contrast

• Probability ≈ Z³ / E³

2. Compton Scatter

In Compton scatter:

• A high-energy X-ray photon interacts with an outer-shell electron.

• The electron is ejected (recoil electron).

• The photon changes direction and continues with reduced energy.

Characteristics:

• Most common interaction in diagnostic radiology

• Produces scattered radiation

• Causes image fog

• Represents a radiation hazard to personnel

IV. Dose–Response Relationships

A dose-response relationship describes the association between radiation dose and the resulting biological effect.

Dose-response curves show how the biological response changes with radiation dose.

Two important concepts:

Threshold

The minimum radiation dose required before a biological effect appears.

Nonthreshold

A situation where any radiation dose can cause a biological effect.

Linear Nonthreshold (LNT) Model

The Linear Non-Threshold Model is used in radiation protection.

Characteristics:

• No safe radiation dose

• Even very small doses can cause damage

• Used to estimate risk for low-level radiation exposure

This model applies to stochastic effects, including:

• Cancer

• Leukemia

• Genetic mutations

Nonlinear Threshold Model

Some radiation effects occur only after a certain threshold dose.

Examples:

• Skin erythema

• Cataracts

These are deterministic (nonstochastic) effects.

V. Late Effects of Radiation

Late radiation effects occur months or years after exposure.

Examples include:

• Leukemia

• Cancer

• Genetic mutations

• Cataracts

• Infertility

Occupational radiation workers are mainly concerned with the late effects of radiation exposure.

Historical examples include:

• Early radiologists developing leukemia

• Hiroshima and Nagasaki survivors

• Radium dial painters developing bone cancer

VI. Biologic Effects of Ionizing Radiation

Law of Bergonié and Tribondeau

This law states that cells are more radiosensitive if they are:

1. Young

2. Undifferentiated

3. Rapidly dividing (high mitotic activity)

Examples of highly radiosensitive cells:

• Lymphocytes

• Bone marrow cells

• Intestinal epithelial cells

• Embryonic cells

Radiosensitive vs Radioresistant Tissues

Highly radiosensitive tissues:

• Lymphocytes

• Bone marrow

• Intestinal epithelium

• Reproductive cells

Radioresistant tissues:

• Muscle tissue

• Nerve tissue

• Mature bone

VII. Radiation Weighting and Tissue Weighting

Different radiation types cause different levels of biological damage.

Radiation Weighting Factor (Wr)

Represents the biologic effectiveness of different radiation types.

Example:

• X-rays: Wr = 1

• Alpha particles: Wr = 20

Tissue Weighting Factor (Wt)

Represents relative radiosensitivity of specific tissues.

Examples:

• Gonads: high weighting factor

• Skin: lower weighting factor

Effective Dose Formula

Effective Dose (EfD) =
Wr × Wt × Absorbed Dose

VIII. Linear Energy Transfer (LET)

LET describes the rate at which radiation deposits energy in tissue.

Higher LET radiation causes greater biological damage.

Examples:

• Alpha particles → high LET

• X-rays → low LET

Relative Biological Effectiveness (RBE)

RBE measures how damaging radiation is compared to X-rays.

Relationship:

Higher LET → Higher RBE → Greater biologic damage

IX. Direct and Indirect Radiation Effects

Direct Effect

Occurs when radiation directly damages DNA molecules.

More common with high-LET radiation.

Indirect Effect

Occurs when radiation interacts with water molecules, producing free radicals that damage DNA.

This is the most common mechanism in diagnostic radiology.

Because the body is 65–80% water, indirect effects predominate.

X. DNA Damage from Radiation

Radiation may cause several types of DNA damage:

• Single-strand break

• Double-strand break

• Cross-linking

• Base damage or mutation

Approximately 90% of radiation-induced damage is repairable.

However, severe or repeated damage can cause:

• Cell death

• Cancer

• Genetic mutation

XI. ALARA Principle

Radiation exposure must always be kept:

As Low As Reasonably Achievable (ALARA).

Radiographers must minimize exposure by:

• Proper collimation

• Correct exposure factors

• Avoiding repeat examinations

• Shielding sensitive organs

• Maintaining equipment quality control

Radiation safety is a professional responsibility of all radiologic technologists.

IV. Genetic Effects

Definition

Genetic effects are radiation effects that occur in the future offspring of exposed individuals due to damage or mutation of reproductive cells (gametes).

These effects do not appear in the exposed person, but rather in their children or future generations.

Mechanism

Radiation can damage the DNA of sperm or ova, causing gene mutation.
If the mutated gene is transmitted during reproduction, it can lead to hereditary disorders.

Important Concept: Genetically Significant Dose (GSD)

Genetically Significant Dose (GSD) refers to the average radiation dose received by the reproductive organs of a population that may affect future generations.

Purpose:

• Used to estimate the genetic impact of radiation exposure on a population

• Helps establish radiation protection standards

Radiation Protection for Reproductive Organs

Females

The ovaries are highly radiosensitive.

Possible effects:

• Infertility

• Genetic mutation in ova

• Potential hereditary abnormalities in offspring

10-Day Rule

The 10-Day Rule states that:

Reason:

• Ovulation has not yet occurred

• The probability of pregnancy is minimal

Patient Questionnaire

Patients are asked about:

• Pregnancy status

• Last menstrual period (LMP)

This helps prevent accidental fetal exposure.

Posting

Radiology departments often place signs reminding patients to inform staff if they are pregnant.

Males

The testes are very radiosensitive.

Possible effects:

• Temporary or permanent sterility

• Reduced sperm production

• Possible genetic mutation in sperm cells

Because of this:

• Gonadal shielding is used whenever possible.

Children

Children are more sensitive to radiation because:

• Cells divide more rapidly

• Tissues are still developing

• They have longer life expectancy, allowing more time for radiation effects to appear

Therefore:

• Radiation exposure must be kept as low as possible.

V. Somatic Effects

Definition

Somatic effects are radiation effects that occur in the exposed individual, not in their offspring.

These effects result from damage to body cells (somatic cells).

Somatic effects may appear:

• Immediately (early effects)

• Years later (late effects)

Major Somatic Effects

1. Carcinogenesis

Carcinogenesis is the development of cancer due to radiation exposure.

Radiation damages DNA, which may cause cells to grow uncontrollably.

Common radiation-induced cancers include:

• Leukemia

• Thyroid cancer

• Breast cancer

• Lung cancer

• Bone cancer

These usually appear years after exposure.

2. Cataractogenesis

Cataractogenesis is the formation of cataracts (lens opacity) caused by radiation damage to the lens of the eye.

Effects:

• Clouding of the lens

• Decreased vision

• Possible blindness in severe cases

The lens is highly radiosensitive.

3. Life Span Shortening

Radiation exposure may reduce life expectancy due to:

• Cellular damage

• Increased cancer risk

• Degeneration of body systems

4. Reproductive Risks

Radiation exposure to reproductive organs may cause:

• Temporary sterility

• Permanent infertility

• Genetic mutations

Embryologic / Fetal Effects

Radiation Effects on the Embryo and Fetus

The developing embryo and fetus are extremely radiosensitive.

Radiation exposure during pregnancy can cause:

• Growth retardation

• Congenital malformations

• Mental retardation

• Childhood cancer

• Fetal death (at high doses)

Critical Periods of Fetal Development

1. Preimplantation Stage (0–2 weeks)

Effect:
All-or-nothing response

Possible outcomes:

• Embryo dies
  OR

• Embryo survives with no damage

2. Organogenesis (2–8 weeks)

This is the most critical stage.

Organs are forming, so radiation may cause:

• Congenital malformations

• Structural abnormalities

3. Fetal Stage (8 weeks – birth)

Possible effects:

• Growth retardation

• Mental retardation

• Functional abnormalities

• Increased cancer risk later in life

Important Radiation Protection Principles for Pregnancy

Radiologic technologists must:

1. Verify pregnancy status

2. Avoid unnecessary examinations

3. Use lead shielding when possible

4. Use lowest radiation dose possible (ALARA principle)

5. Consult the radiologist if pregnancy is suspected

Ultra-High Yield Board Exam Points

These are frequently tested facts:

• Genetic effects affect future generations
• Somatic effects affect the exposed individual
• Gonads are highly radiosensitive
• 10-Day Rule protects possible early pregnancy
• Organogenesis is the most sensitive fetal stage
• Radiation may cause cancer, cataracts, and genetic mutation
• Children are more radiosensitive than adults

Patient Protection

Radiologic imaging professionals have the ethical and professional responsibility to minimize radiation exposure to patients, themselves, and the public.

Although diagnostic imaging provides significant medical benefits, exposure to ionizing radiation carries potential long-term biologic risks. Therefore, radiation exposure must always follow the ALARA principle (As Low As Reasonably Achievable).

Ways to achieve patient protection include:

• Beam restriction

• Proper exposure factors

• Filtration

• Shielding

• Proper patient communication

• Accurate positioning

• Use of automatic exposure control (AEC)

• Appropriate image receptors

• Use of grids or air-gap techniques

• Safe fluoroscopic practice

I. Beam Restriction

Beam restriction refers to limiting the size of the x-ray beam to the area of diagnostic interest.

It is considered the most important method of reducing patient radiation dose.

A. Purpose

Beam restriction serves several important purposes:

1. Reduce Patient Radiation Dose

Only tissues necessary for diagnosis are exposed.

2. Reduce Scatter Radiation

Smaller irradiated areas produce less scattered radiation.

3. Improve Image Quality

Scatter radiation produces radiographic fog, which decreases contrast and image clarity.

Therefore, beam restriction improves both patient safety and radiographic image quality.

B. Types of Beam Restrictors

There are three types of beam restriction devices:

1. Aperture diaphragms

2. Cones (cylinders)

3. Collimators

1. Aperture Diaphragm

The aperture diaphragm is the simplest beam restrictor.

Structure

• Flat piece of lead (Pb)

• Has a central opening

• The opening determines the shape and size of the x-ray beam

Common Uses

• Skull units

• Some chest radiography units

Advantages

• Simple design

• Easy to use

Disadvantages

• Opening size is fixed

• Field size cannot be adjusted

To change field size, a different diaphragm must be used.

2. Cones (Cylinders)

Cones are lead-lined cylindrical devices attached to the x-ray tube or collimator.

Types

• Straight cylinder cone

• Flared cone

Some cones are extendable (telescopic).

Uses

• Small anatomical areas such as:

  • Paranasal sinuses

  • L5–S1

  • Small localized structures

Advantages

• More efficient than aperture diaphragms

• Restrict the beam over a longer distance

Disadvantages

• Fixed opening size

• Limited to small field sizes

3. Collimators

The collimator is the most efficient beam restricting device.

It is attached directly to the X-ray tube housing.

Components

Collimators contain two sets of adjustable lead shutters (blades):

1. Upper shutters

2. Lower shutters

The lower shutters control the length and width of the radiation field.

This allows the radiographer to precisely control field size and shape.

C. Light-Localization Apparatus

The collimator contains a light-localization system.

This system allows visualization of the X-ray field before exposure.

Components

• Light bulb

• Mirror

The mirror reflects the light to produce a visible light field corresponding to the X-ray beam.

Important Principle

For proper alignment:

The x-ray tube focal spot and light bulb must be the same distance from the mirror.

If alignment is incorrect:

• The light field and x-ray field will not match

• An incorrect exposure area may occur

• Repeat examinations may be required

D. Accuracy

Collimator accuracy must be regularly checked through quality assurance (QA) programs.

NCRP Standard

Manual collimation must be accurate within:

±2% of the Source-to-Image Distance (SID)

Example:

If SID = 100 cm
Maximum error = 2 cm

Positive Beam Limitation (PBL)

Most modern radiographic systems use Positive Beam Limitation (PBL).

Definition

PBL automatically adjusts the x-ray beam size to match the image receptor size.

Sensors in the Bucky tray detect cassette size and adjust the collimator shutters.

Advantages

• Prevents unnecessary exposure

• Ensures correct beam restriction

• Produces an unexposed border on the radiograph

NCRP Standard

• Accuracy within 3% per side

• Maximum 4% total misalignment

II. Exposure Factors

Exposure factors significantly influence patient radiation dose.

A. mAs and kV

mAs (milliampere-seconds)

mAs controls the quantity (number) of X-ray photons produced.

Increasing mAs:

• Increases radiation output

• Increases patient dose

kVp (kilovoltage peak)

kVp controls the energy and penetrability of the X-ray beam.

Increasing kVp:

• Produces more high-energy photons

• Increases beam penetration

• Decreases radiation absorption by the patient

Optimal Technique

To minimize dose:

Use high kVp and low mAs whenever possible.

Benefits:

• Lower patient dose

• Reduced tube heat

• Longer x-ray tube life

B. Generator Type

Modern radiographic systems often use:

• Three-phase generators

• High-frequency generators

These generators produce a more constant voltage.

Benefits:

• More efficient x-ray production

• Slightly reduced patient dose

• Improved image quality

III. Filtration

The X-ray beam contains many low-energy photons.

Low-energy photons:

• Cannot penetrate the patient

• Are absorbed by tissues

• Increase patient skin dose

Filtration removes these photons.

A. Inherent Filtration

Inherent filtration consists of materials permanently built into the X-ray tube housing.

Sources include:

• Glass envelope of the tube

• Insulating oil

• Collimator mirror

• Tube housing window

Typical value:

≈1.5 mm aluminum equivalent

B. Added Filtration

Added filtration refers to thin aluminum sheets placed in the beam path.

Purpose:

• Remove low-energy photons

• Increase average beam energy

• Reduce patient skin dose

C. NCRP Filtration Guidelines

Minimum total filtration:

Total filtration = Inherent + Added filtration

IV. Shielding

Shielding protects radiosensitive organs from unnecessary radiation exposure.

Highly radiosensitive organs include:

• Gonads

• Lens of the eye

• Bone marrow

• Thyroid

• Breast tissue

A. Rationale for Use

Shielding should be used whenever:

1. Gonads are within 5 cm of the primary beam

2. Patient has reproductive potential

3. The shield does not interfere with the diagnosis

B. Types of Shields

1. Flat Contact Shields

• Flat lead-impregnated vinyl

• Placed directly over the gonads

Limitation:

• Only useful for AP or PA recumbent positions

2. Shadow Shields

Attached to the x-ray tube housing.

Advantages:

• Can be used for multiple patient positions

• Do not contaminate sterile fields

3. Contour (Shaped) Shields

Shaped to fit the male gonads.

Held in place by disposable briefs.

Very effective for many positions.

4. Breast Shields

Used during procedures such as scoliosis imaging.

Often used in:

• Spinal stoles

• Compensating filters

Performing scoliosis studies in PA projection reduces breast dose significantly.

C. Patient Position

Positioning can reduce radiation exposure.

Examples:

• PA abdominal radiography reduces gonadal dose

• PA skull imaging reduces lens exposure

• PA scoliosis imaging reduces breast exposure

V. Reducing Patient Exposure

A. Patient Communication

Good communication:

• Builds patient confidence

• Improves cooperation

• Reduces motion

• Prevents repeat exposures

Repeat exposures increase:

• Patient dose

• Facility cost

B. Patient Positioning

Accurate positioning ensures:

• Correct anatomy visualization

• Avoidance of repeat examinations

Positioning is especially important when using AEC systems.

C. Automatic Exposure Control (AEC)

AEC automatically terminates exposure when adequate radiation reaches the detector.

Purpose:

• Maintain consistent image density

• Prevent overexposure

1. Ionization Chamber

Located between the patient and the image receptor.

Measures radiation passing through the patient.

Exposure stops when a preset level is reached.

2. Phototimer

Located behind the image receptor.

Uses a fluorescent screen and a photomultiplier tube to detect radiation.

3. Backup Timer

Prevents excessive exposure if the AEC fails.

4. Minimum Response Time

The shortest exposure time possible for the AEC.

If the exposure time required is shorter than this, the image may become overexposed.

VI. Image Receptors

Faster image receptor systems require less radiation.

Rare-earth screens are commonly used because they:

• They are four times faster than calcium tungstate screens

• Require a lower radiation dose

Digital imaging also reduces dose due to:

• Increased detector sensitivity

• Efficient image capture

VII. Grids and Air-Gap Technique

Grids

Grids remove scattered radiation before it reaches the image receptor.

Benefits:

• Improved radiographic contrast

Disadvantage:

• Requires increased exposure (mAs)

Air-Gap Technique

Creates distance between the patient and the image receptor.

Scatter radiation diverges and misses the receptor.

It can function similarly to a low-ratio grid.

Common example:

• Lateral cervical spine imaging at 72-inch SID without a grid

VIII. Fluoroscopy

Fluoroscopy generally delivers higher radiation doses than standard radiography.

Reasons:

• X-ray tube closer to the patient

• Longer exposure times

Protective measures include:

• High kVp technique

• Proper collimation

• Limiting exposure time

• Using pulsed fluoroscopy

Fluoroscopy units include a 5-minute cumulative timer.

IX. NCRP Recommendations for Patient Protection

Important standards include:

• Minimum 2.5 mm Al filtration for >70 kVp
• Exposure reproducibility variation must not exceed 5%
• Linearity variation must not exceed 10%
• Tube leakage radiation must be <100 mR/hr at 1 meter
• Minimum 12-inch SSD for radiography
• Minimum 15-inch SSD for stationary fluoroscopy
• Fluoroscopy beam intensity <10 R/min
• 5-minute cumulative fluoroscopy timer required
• Collimation accuracy within 2% SID
• SID indicator accuracy within 2%

ULTRA HIGH-YIELD BOARD FACTS

These are very commonly tested:

• Beam restriction is the most effective method of reducing patient dose
• Collimator = most efficient beam restrictor
• High kVp and low mAs reduce patient dose
• Minimum filtration >70 kVp = 2.5 mm Al
• Gonadal shielding is used if within 5 cm of the beam
• AEC stops exposure automatically
• Grids improve contrast but increase patient dose
• Fluoroscopy requires a 5-minute timer

Personnel Protection

Personnel protection refers to methods used to minimize radiation exposure to radiologic workers such as radiographers, radiologists, and other healthcare personnel.

The most important principle in personnel protection is the ALARA principle, meaning radiation exposure must be kept As Low As Reasonably Achievable.

Radiation exposure to personnel mainly comes from secondary radiation, especially scatter radiation from the patient.

I. GENERAL CONSIDERATIONS

A. Occupational Exposure

Radiographers must avoid unnecessary radiation exposure and ensure that patients’ radiation dose is kept to the minimum necessary for diagnostic imaging.

Sources of Radiation Exposure to Radiographers

Radiation exposure can come from:

1. Primary Radiation

2. Secondary Radiation

   • Scatter radiation

   • Leakage radiation

Radiographers must never be exposed to the primary (useful) beam.

Most Important Source of Scatter

The patient is the principal source of scattered radiation in diagnostic radiology.

Other scattering objects include:

• X-ray table

• Bucky-slot cover

• Control booth wall

Occupational Dose Monitoring

The National Council on Radiation Protection and Measurements (NCRP) recommends personal radiation monitoring for individuals who may receive 10% of the occupational dose limit.

Occupational Dose Limit

Maximum occupational dose limit:

5 rem per year (50 mSv/year)

Therefore, monitoring is required if exposure may reach:

0.5 rem/year (5 mSv/year)

B. ALARA (As Low As Reasonably Achievable)

ALARA is the fundamental radiation safety philosophy used in radiology.

It means radiation exposure must be kept as low as reasonably achievable, even if exposures are below the legal limits.

Methods Used to Maintain ALARA

1. Radiation monitoring devices (dosimeters)

2. Regular radiation safety training

3. Radiation safety orientation for new employees

4. Radiation surveys of radiologic facilities

5. Review of monthly dosimeter reports

Monthly radiation monitoring reports are considered legal documents and must be carefully reviewed.

Even very small exposures should be reduced whenever possible.

II. OCCUPATIONAL RADIATION SOURCES

A. Scattered Radiation

Scatter radiation occurs when primary X-ray photons interact with matter and change direction.

This usually occurs through the Compton interaction.

Importance in Radiology

Scatter radiation is the most significant occupational radiation hazard in diagnostic radiology.

This is particularly important during:

• Fluoroscopy

• Mobile radiography

During fluoroscopy, high kilovoltage techniques produce energetic Compton scatter from the patient.

Scatter Radiation Intensity

The intensity of scatter radiation at 1 meter from the patient is approximately:

0.1% of the primary beam intensity

Because of this, the patient is considered the most important source of scatter radiation.

Other Scatter Sources

Additional sources include:

• X-ray table

• Bucky-slot cover

• Control booth wall

B. Leakage Radiation

Leakage radiation is radiation that escapes from the X-ray tube housing in directions other than the primary beam.

NCRP Leakage Radiation Limit

According to NCRP regulations:

Leakage radiation must not exceed 100 mR per hour at a distance of 1 meter from the X-ray tube housing.

This limit ensures that radiation leakage from the tube housing remains minimal and safe.

C. NCRP Guidelines

The National Council on Radiation Protection and Measurements (NCRP) establishes guidelines to ensure radiation safety.

Important Equipment Safety Requirements

1. The control panel must indicate when X-rays are being produced.

   • Usually by a visible or audible signal

2. The exposure switch must be a dead-man switch.

A dead-man switch means the operator must continuously press the switch for the exposure to occur. If released, exposure stops immediately.

3. The exposure switch must be located so that it cannot be operated outside the shielded control booth.

Rules for Selecting Someone to Assist a Patient

If a patient cannot hold the required position (e.g., children or weak patients), assistance may be required.

Guidelines include:

• Preferably a male older than 18 years

• A female older than 18 years who is not pregnant may also assist.

• Must wear protective apparel

• Must stand as far as possible from the beam

• Must never stand in the path of the useful beam

Radiology personnel must never hold the patient during exposures.

Instead, use:

• Mechanical restraining devices

• Patient relatives (if necessary)

Fluoroscopy Protection Guidelines

Several NCRP recommendations apply during fluoroscopic procedures:

• Image intensifier must provide 2.0 mm lead equivalent protection

• The exposure switch must be a dead-man type

• Undertable fluoroscopic tubes must have a Bucky-slot cover with 0.25 mm Pb equivalent

• A cumulative timer must alert the operator after 5 minutes of fluoroscopy

• Table-side lead drapes must have 0.25 mm Pb equivalent

• Protective lead aprons must be 0.50 mm Pb equivalent

• Lead gloves must be 0.25 mm Pb equivalent

• Hands must never be placed in the useful beam

• Maximum fluoroscopic exposure rate: 10 R/min

III. FUNDAMENTAL METHODS OF PROTECTION

A. Cardinal Rules of Radiation Protection

The three cardinal principles of radiation protection are:

1. Time

2. Distance

3. Shielding

These are the most effective ways to reduce radiation exposure.

Time

Reducing the time of radiation exposure reduces radiation dose.

Example:

If a worker receives 10 mrem in 1 hour, then 30 minutes exposure results in 5 mrem.

Distance

Increasing the distance from the radiation source greatly reduces exposure.

This is described by the Inverse Square Law.

Shielding

Placing a barrier between the radiation source and the worker reduces exposure.

Examples:

• Lead walls

• Lead aprons

• Lead shields

B. Inverse Square Law

The Inverse Square Law states:

Radiation intensity is inversely proportional to the square of the distance from the source.

Formula concept:

If distance doubles → exposure becomes 1/4

Example:

If 40 mrem is received at 40 inches, then at 80 inches the exposure becomes 10 mrem.

Increasing distance is therefore one of the most effective protection methods.

IV. PRIMARY AND SECONDARY BARRIERS

A. Primary Barriers

Primary barriers protect against the primary (useful) x-ray beam.

Examples include:

• Radiographic room walls

• Lead doors

Typical primary barrier thickness:

1/16 inch (1.5 mm) lead

Primary barriers are usually 7 feet high.

B. Secondary Barriers

Secondary barriers protect against:

• Scatter radiation

• Leakage radiation

Examples include:

• Upper portions of walls

• Control booth wall

• Lead aprons

Secondary barriers typically require:

1/32 inch lead thickness

Important:

Secondary barriers do not protect against the primary beam.

Control Booth

The control booth protects the radiographer from radiation exposure.

Requirements include:

• Shielded barrier

• Leaded glass window (about 1.5 mm Pb equivalent)

• Exposure switch inside the booth

The primary beam must never be directed toward the control booth.

B. Protective Apparel and Care

Protective apparel used by radiologic personnel includes:

• Lead aprons
• Lead gloves
• Thyroid shields
• Leaded eyewear

Required Lead Equivalents

Lead aprons: 0.50 mm Pb equivalent

Lead gloves: 0.25 mm Pb equivalent

Thyroid shields: 0.50 mm Pb equivalent

These are secondary protective devices, meaning they protect against scatter radiation but not the primary beam.

Care of Protective Apparel

Protective equipment must be handled properly.

Guidelines include:

• Hang aprons on proper racks
• Never fold lead aprons
• Do not drop them on the floor

Improper handling can cause cracks in the lead material, reducing protection.

Protective apparel must be radiographically inspected annually to detect cracks.

C. Protective Accessories

Additional protection devices include:

Mobile Lead Barriers

Mobile lead shields provide full body protection from scattered radiation.

They are used when personnel must remain in the room during exposure.

Lead Apron Under Pillow Technique

During some fluoroscopic procedures (e.g., GI or barium enema), a lead apron may be placed under the patient’s pillow to protect the radiographer assisting at the head of the table.

V. SPECIAL CONSIDERATIONS

A. Pregnancy

Pregnant radiographers require special radiation protection considerations.

Declaration of Pregnancy

The radiographer should declare pregnancy in writing to her supervisor.

Once declared:

• Occupational exposure history is reviewed
• A fetal monitor (baby badge) is issued

Fetal Dosimeter Placement

The fetal monitor is worn:

Under the lead apron at waist level

Fetal Dose Limit

Maximum fetal radiation dose during pregnancy:

500 mrem (5 mSv)

Under normal conditions, typical occupational exposures are far below this limit.

B. Mobile Radiography

Mobile radiography requires additional protection measures.

Guidelines include:

• Each mobile unit must have a lead apron

• Radiographer must stand as far away as possible

• Exposure cord must allow the radiographer to stand at least 6 feet from the patient

• Lead apron must be worn during exposure

C. Fluoroscopic Units and Procedures

Fluoroscopy produces higher radiation doses than routine radiography.

Required Source-to-Skin Distance

Minimum:

12 inches (30 cm)

Preferred:

15 inches (38 cm)

Fluoroscopic Exposure Limits

Maximum tabletop exposure rate:

10 R/min

Typical fluoroscopic current:

1–3 mA

Maximum:

5 mA

Fluoroscopic Protection Requirements

• Image intensifier must provide 2.0 mm Pb equivalent protection

• Bucky-slot cover must provide 0.25 mm Pb equivalent

• Protective curtain/drape must provide 0.25 mm Pb equivalent

• Total filtration must be 2.5 mm Al equivalent

• Cumulative timer must alert after 5 minutes

• Beam collimation must be visible on monitor

HIGH-YIELD EXAM POINTS

Most occupational exposure occurs during:

Fluoroscopy and mobile radiography

Most important scatter source:

The patient

Cardinal radiation protection rules:

Time – Distance – Shielding

Maximum occupational dose:

5 rem/year (50 mSv/year)

Maximum fetal dose:

500 mrem (5 mSv)

Leakage radiation limit:

100 mR/hr at 1 meter

Fluoroscopy exposure rate limit:

10 R/min

Radiation Exposure and Monitoring

The Three Things We Measure in Radiation

Radiation measurement focuses on three different concepts.

Students often confuse them, so remember this structure:

We will learn each one.

Lesson 3 — Exposure (Roentgen)

Exposure tells us:

The unit used is:

Roentgen (R)

Key idea:

Roentgen measures charge produced in air by x-rays or gamma rays.

Important points:

• applies only to photons (x-rays and gamma rays)
• measures ionization in air
• not used for tissue dose

SI Equivalent

The SI unit replacing Roentgen is:

Coulomb per kilogram (C/kg)

Conversion:

1 R = 2.58 × 10⁻⁴ C/kg

Example

If x-rays pass through air and produce a lot of ionization, the Roentgen value increases.

But remember:

Roentgen does not tell us how much dose the patient absorbs.

For that we need another unit.

Board Exam Tip

If the question asks:

“Unit of ionization in air”

The answer is:

Roentgen

Absorbed Dose (Rad / Gray)

Exposure tells us what happens in the air, but doctors need to know:

This is called:

Absorbed Dose

Definition:

Energy deposited in 1 kilogram of material.

Traditional Unit

Rad

Rad stands for:

Radiation Absorbed Dose

SI Unit

Gray (Gy)

Conversion:

100 rad = 1 Gray

Example

If tissue absorbs radiation energy:

• molecules break
• chemical reactions occur
• cells may be damaged

That’s why absorbed dose is important in biology and medicine.

Board Exam Tip

Question:

Unit measuring energy absorbed by tissue?

Answer:

Rad or Gray

Biological Damage (Rem / Sievert)

Different types of radiation cause different levels of biological damage.

Example:

Alpha particles cause much more damage than x-rays.

Even if the absorbed dose is the same.

To account for this we use:

Dose Equivalent

Dose equivalent measures:

Unit

Rem

Rem means:

Radiation Equivalent Man

Formula:

Dose Equivalent = rad × Quality Factor

SI Unit

Sievert (Sv)

Conversion:

100 rem = 1 Sv

Example

If a patient receives:

1 rad of x-rays → 1 rem

But:

1 rad of alpha particles → 20 rem

Because alpha radiation is much more damaging.

Quality Factor (QF)

Quality Factor represents:

Typical values:

Radiographers mostly deal with:

Low QF radiation (x-rays).

Linear Energy Transfer (LET)

Another concept related to biological damage is:

Linear Energy Transfer

LET describes:

High LET Radiation

Characteristics:

• deposits energy rapidly
• causes severe damage

Examples:

• alpha particles
• neutrons

Low LET Radiation

Characteristics:

• spreads energy over a distance
• causes less damage

Examples:

• x-rays
• gamma rays
• beta particles

Radiology uses low LET radiation.

Why Radiation Monitoring Is Needed

Radiographers work near radiation sources every day.

To ensure safety we must measure occupational exposure.

Monitoring devices help:

• measure worker dose
• ensure legal limits are not exceeded
• track lifetime exposure

Monitoring is required for workers who might receive:

Dosimeters (Radiation Monitors)

A dosimeter measures how much radiation a worker receives.

The most common types are:

1. OSL dosimeter

2. TLD dosimeter

3. Film badge

4. Pocket dosimeter

We’ll study them one by one.

OSL Dosimeter (Most Common Today)

OSL means:

Optically Stimulated Luminescence.

Material used:

Aluminum oxide (Al₂O₃).

How It Works

1. Radiation hits the crystal.

2. Energy becomes trapped inside the crystal.

3. A laser stimulates the crystal.

4. The crystal releases blue light.

5. Light intensity = radiation dose.

Advantages

• very sensitive
• detects ~1 mrem
• reusable readings
• resistant to heat and moisture

Because of this, OSL is the most widely used dosimeter today.

TLD Dosimeter

TLD means:

Thermoluminescent Dosimeter.

Material:

Lithium fluoride (LiF).

How It Works

1. Radiation stores energy in the crystal.

2. Crystal is heated in a reader.

3. Heat releases light.

4. Light intensity indicates radiation dose.

Advantages

• very accurate
• not affected by heat or humidity
• reusable

Minimum detectable dose:

~5 mrem

Film Badge

Film badges use:

photographic film.

Radiation darkens the film.

The darker the film, the higher the dose.

Filters Used

Film badges contain metal filters such as:

• aluminum
• copper
• open window

These help determine:

• radiation energy
• radiation type

Disadvantages

• sensitive to heat
• sensitive to humidity
• must be processed monthly

Because of these issues, film badges are being replaced by OSL dosimeters.

Pocket Dosimeter

Pocket dosimeters provide immediate readings.

They look like small penlights.

Inside is a tiny ionization chamber.

When radiation enters:

• air becomes ionized
• electrical charge changes
• a fiber moves inside the device

You read exposure through the eyepiece.

Measurement Range

Usually:

0–200 mR

Limitation

Pocket dosimeters do not create permanent records, so they are usually used in high-exposure situations.

Where to Wear Dosimeters

Standard placement:

Collar level outside the lead apron

This measures exposure to:

• head
• neck
• thyroid
• eyes

Pregnant Workers

Two badges are used:

1. Collar badge (outside apron)

2. Fetal badge (under apron at waist)

This estimates radiation to the fetus.

Ring Dosimeter

Used when hands are near radiation.

Common in:

• fluoroscopy
• interventional radiology
• nuclear medicine

Measures dose to fingers.

Radiation Dose Limits

Dose limits are recommended by the
National Council on Radiation Protection and Measurements (NCRP).

Occupational Worker Limit

Annual limit:

5 rem (50 mSv)

Applies to workers 18 years and older.

Public Limit

0.5 rem (5 mSv) per year.

Pregnant Worker

Total fetal dose limit:

0.5 rem (5 mSv).

Monthly limit:

0.05 rem (0.5 mSv).

ALARA Principle

ALARA stands for:

As Low As Reasonably Achievable.

Goal:

Minimize radiation exposure.

Three protection methods:

1. Time – reduce exposure time

2. Distance – increase distance from source

3. Shielding – use lead barriers

Key Concepts to Remember

Exposure → Roentgen
Absorbed Dose → Rad / Gray
Biological Effect → Rem / Sievert