Radiation Safety Principles and Dose Management in Medical Imaging

Is there a safe dose of radiation for patients?

There is no safe dose—always a chance of cancer or genetic effects.

Name 3 types of photon interaction with matter.

Transmit, absorb, scatter.

What is primary radiation?

Radiation that comes directly from the x-ray tube.

What is scatter radiation?

Secondary radiation that degrades image quality and increases patient & occupational dose.

How does increasing KVP affect patient dose?

Increases scatter escape → decreases patient dose (Exception: if mAs also increases, dose ↑).

How does increasing SID affect dose?

Dose decreases (inverse square law + increased distance).

How does filtration affect dose?

Filtration removes low-energy photons → decreases skin dose.

What is a compensating filter used for?

Even out the radiation dose across a body part that has uneven thickness or density.

How does receptor sensitivity (speed) affect dose?

Higher speed = less dose needed.

How do grids affect dose?

Improve contrast by absorbing scatter, but increase patient dose (need higher technique).

What effect do repeats have on dose?

Increase dose unnecessarily (poor positioning/equipment).

How does collimation/field size affect dose?

Smaller field size (tight collimation) = less dose.

What is AEC (Automatic Exposure Control) and how can it increase dose?

AEC stops exposure when enough radiation reaches the receptor. Incorrect chamber selection → repeat images & ↑ dose.

What does ALARA stand for?

As Low As Reasonably Achievable.

What are the 3 Cardinal Rules of radiation protection?

Minimize time, maximize distance, use shielding.

What is the inverse square law effect?

Double distance = dose decreases by factor of 4.

Where should you wear a radiation badge?

Between neck & waist, under lead apron, front of body.

What does the control badge measure?

Measures background radiation during transport.

How does a TLD work?

Lithium fluoride crystal stores radiation → heat releases light → light is measured.

How does an OSLD work?

Aluminum oxide crystal stores radiation → laser releases light → light is measured.

What does 'M' or '-' mean on a dosimetry report?

Minimal dose (<1 millirem of exposure).

What is the annual dose limit for pregnant technologists?

4 mSv (for remainder of pregnancy).

Fetal exposure effects at 0-2 weeks.

Prenatal death (lethal).

Fetal exposure effects at 10 days - 6 weeks.

Neonatal death (lethal) or congenital abnormalities.

Fetal exposure effects at 2 weeks - 6 weeks.

Intellectual disabilities.

Fetal exposure effects later in pregnancy.

Malignancy/cancer risk (linear, no threshold).

Protective lead aprons for patients and operators must provide ___ of lead equivalency for 100 kV or less.

0.25 mm.

Protective lead aprons for patients and operators must provide ___ of lead equivalency for >100 kV and <150 kV.

0.35 mm.

Protective lead aprons for patients and operators must provide ___ of lead equivalency for 150 kV or greater.

0.5 mm.

For interventional procedures, protective thyroid shields must provide ___ of lead equivalency.

0.5 mm.

Protective gloves or gauntlets must possess at least ___ of lead equivalency.

0.25 mm.

All protective equipment must be tested on a ____ basis for integrity.

Yearly.

Ceiling-mounted lead acrylic screens and moveable shields should provide protection equivalent to at least ___ of lead equivalency.

0.5 mm.

What should a technologist do if they encounter questionable exam conditions?

The technologist may withdraw from the exam and inform their supervisor.

What rights do technologists have regarding unsafe equipment or patients?

Technologists have the right to refuse to work with unsafe equipment or patients.

What should a technologist do if they find themselves in a dangerous situation?

By being knowledgeable, which helps the patient to co-operate and believe what is said.

What should technologists do when addressing patients' fears about radiation?

They should compare radiation exposure to other radiation risks and other kinds of risks, and provide factual information.

What is the annual whole body dose limit for a radiation worker?

20 mSv effective dose per year averaged over a defined 5 year period (i.e. a limit of 100 mSv in 5 years) and 50 mSv in any single year.

What is the annual whole body dose limit for a member of the public?

1 mSv effective dose.

What is the annual dose limit to the lens of the eye for a radiation worker?

20 mSv equivalent dose per year averaged over a defined 5 year period and 50 mSv in any single year.

What is the annual dose limit to the lens of the eye for a member of the public?

15 mSv.

What is the annual dose limit to the skin for a radiation worker?

500 mSv equivalent dose.

What is the annual dose limit to the skin for a member of the public?

50 mSv equivalent dose.

What is the annual dose limit to the hands and feet for a radiation worker?

500 mSv equivalent dose.

What is the annual dose limit to the hands and feet for the member of the public?

There is no dose limit for this category.