RAD 301: Radiation Biology

Annual occupational whole-body effective dose limit

50 mSv (5 rem).

Primary source of occupational exposure

Scatter radiation from the patient.

Protective apparel

Lead aprons, gloves, and thyroid shields.

Reduce exposure _______ to limit radiation dose.

time

Increase _______ from the radiation source; it is the most effective protection for radiographers.

distance

Protective barriers to reduce exposure

shielding; primary and secondary barriers

Inverse square law

Doubling distance reduces exposure to one-fourth.

Photoelectric absorption

A photon is completely absorbed, ejecting an inner-shell electron.

Photoelectric absorption: image and dose

Produces high subject contrast but increases patient dose.

Compton scatter

A photon interacts with an outer-shell electron and is partially absorbed and scattered.

Compton scatter contributes to image fog

Scatter reaching the receptor creates unwanted density and reduces contrast.

Coherent scattering

A very low-energy photon changes direction NO ionization; also called Thomson scattering.

Pregnant trauma patient: exposure factors

Use the lowest exposure factors that produce a diagnostic image.

Pregnant trauma patient: collimation

Precaution: Collimate precisely to the area of interest.

Pregnant trauma patient: shielding

Shield the lower abdomen and pelvis when appropriate.

ALARA

As Low As Reasonably Achievable.

Declared pregnant worker: second dosimeter placement

Wear it under the apron at waist level to monitor embryo/fetus dose.

Total gestational (total pregnancy term) dose limit

5 mSv (0.5 rem).

Monthly embryo/fetus dose limit

0.5 mSv (0.05 rem).

Radiosensitivity and effect on cell division

cells are ______ b/c they are rapidly dividing cells have greater potential for radiation damage.

Law of Bergonié and Tribondeau

law that states Cells are most radiosensitive when rapidly dividing, immature, and poorly differentiated.

Radiosensitive tissue examples

Bone marrow, reproductive cells, and intestinal epithelium.

Natural background radiation

Includes cosmic radiation, terrestrial radiation, internal radionuclides, and radon gas.

Beam restriction

Collimate the radiographic beam no larger than the image receptor.

Benefits of collimation

Reduces patient dose and scatter, improves contrast, and supports ALARA.

Radiopaque

Absorbs more x-ray photons and appears white or light. example: bone

Radiolucent

Allows x-rays to pass easily and appears black or dark. example: air

Radiation absorption and patient dose

Greater absorption deposits more energy in tissues and increases patient dose.

Cell

Basic unit of living matter; fundamental to structure, function, and development.

Nucleus

Contains DNA and controls most cell activities, including growth and reproduction.

Mitochondria

Produce energy for cellular functions. “powerhouse of the cell” “power plant”

Personnel radiation monitoring

Radiation workers are monitored with a dosimeter, such as an OSL dosimeter.

Dosimeter placement during fluoroscopy

At collar level, outside the lead apron.

Mobile radiography distance

Stand at least 72 inches (6 feet) from the patient and x-ray tube.

Mobile radiography positioning

Whenever possible, stand at a right angle to the primary beam.

Erythema (deterministic)

Diffuse redness of the skin; a short-term somatic radiation effect.

Desquamation (deterministic)

Shedding of the outer layer of skin; a short-term somatic radiation effect.

Somatic (short term) effects

nausea, fatigue, blood and intestinal disorders, erythema and desquamation

Ionization by x-rays

X-rays remove electrons from atoms, creating ion pairs that can damage cells and DNA.

X-ray beam quality

Penetrating power is controlled by kVp; higher kVp increases penetration.

Lower kVp

Produces less penetration and increased absorption.

mAs

Controls x-ray quantity, or the number of x-rays.

DNA

The most radiosensitive nuclear macromolecule; controls cell reproduction and function.

Radiation injury

DNA damage may cause cell death, mutations, or cancer; visible effects follow a latent period.

Latent period

The time between the initial exposure to radiation and the appearance of visible effects.

Stochastic effects

Can occur at any radiation dose; probability increases; no threshold

Deterministic effects

Certain amount of radiation must be received before an effect can occur; severity increases; threshold