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Biological Effects of

Jennifer Walker, MSEd, R.T.(R)(CT)(MR)

Sandi Watts, MHA, R.T.(R)

Radiation—the transfer of kinet

ic energy, g

ion,

diat

iat

ule

that is in their path. T

lters the

atom or molecule and creates an .

Therefore, the term

used when describing x-. T

.1 Ionizing

iat

ama

a cellular level when x-rays

interact with at that compose the

molecular structures of the anatomy

being radiate

c

ical

ll)

i

lit

injury and abnorma

ies in the

product

ree electrons

produc

ion of low-energy x-ray

photons

The effects of ionizing radiation

vary depending on the particular organ

and tissue exposed. Exposure to ion-

izing radiation can affect the individu-

al exposed, their descendants, or both,

and it can lead to cancer, a shorter lifes-

pan, developmental abnormalities,

genetic mutations, and degenerative

diseases.2 The effects of ionizing radia-

tion exposure are classified as somatic

(occur in exposed individual) or genet-

ic (occur in descendants of exposed

individual).2

Medical iat exposure results

ili

ical

near medicine.

Diagnostic x-ray radiation, such as i-

, and computed

After completing this article, the reader should be able to:

 Explain potential injuries and risks of radiation exposure.

 List characteristics associated



es.

 Describe radiation protection measures for the patient.

As the profession continues

to grow, it is important for

radiologic technologists

to maintain their focus on

protecting their patients,

themselves, and other

health care workers from

unnecessary radiation

exposure. This article

reviews how x- are

produced, how they interact

with the body’s ms, and

how they can damage cells

and tissues. Different types

of radiation damage and

radiation-induced illness

are discussed, along with

recommended exposure

limits. Finally, techniques

for minimizing exposure

are highlighted, including

the triad of time

monitoring for technolog

and tips for conducting

high-quality examinations

while keeping dose as low as

reasonably achievable.

Directed Reading

assorted variety of cells. Radiologic technologists learn

biology when studying human anatomy and physiology;

radiation physics is learned through studying x- pro-

duction and imaging processes.

- Production

The x-ray tube is a component of the x-ray imaging

system that rarely is seen by radiologic technologists

because it is contained in a protective

t cal

he cathode and a positive

t called the anode (see Figure 1). The tube is

constructed of glass or metal and provides a constant

uum, which allows an efficient production of x-rays

and enables a longer tube life.

The cathode is referred to as the cathode assembly

and consists of the filament wires, a focusing cup, and

associated wiring. T

ic cloud, conduct a high voltage to

the gap between t

thode and anode, and focus the

t stream as it heads toward the anode (ie, target

area).2 A

he technologist depresses the expose button

on the console, current (ie, milliamperage) is sent to the

filament wires. The current causes the wires to become

so hot that the outer shell electrons are ejected off the

wires. This phenomenon is known as thermionic emis-

sion, or the boiling off of electrons.4 Because electrons

are negatively charged, they tend to diverge away from

each other. The focusing cup narrows the thermionic

cloud of electrons as they move toward the anode.

The a

he an

and

consists of the a

, stator, and rotor. lso serves as

the path for a high-voltage flow during e

2 The

ano

into the x- generator circuitry.

It serves as a target area for the high-voltage elec-

trons that are ejected from the filament wires,

thereby becoming the source of the x-ray tons.

It serves as the primary thermal conductor.

ium-alloyed tu

is used as the target mate-

rial. As the technologist pushes the exposure button of

the imaging system, there is a short delay before an expo-

sure is made. This allows the rotor to accelerate to its des-

ignated speed while the filament is heated. Only then is

tomography (CT), and

icine procedures are

the 2 largest sources of artificial iation. As of 2006,

they accounted for 48% of the total collective ef

tive

of the U.S. populat

The goal of modern

.1l

maging

essar

zing radi-

.1 Ex

ure to rad

ion can be kept as low as rea-

sonably achievable (ALARA) by3:

collimating the x-am



irec-



ing t

si-

rin

standi

using personal protective equipment (eg, lead

aprons, glasses, and thyroid shields)

Physics

Physics is a branch of the physical sciences that

examines the interrelationship of matter and energy.

Matter has shape and form and occupies space. Matter

can be classified as a pure substance or a mixture of

pure substances. A pure substance is a form of matter

that has a fixed composition. Substances can be simple

(ie, an element) or complex (ie, a compound). In radi-

ography, technologists work with elements such as bar-

ium, tungsten, and lead. The human body also contains

elements including ca

, and oxygen. The

simplest form of an element that still retains that ele-

ment’s chemical properties is known as an atom.4 When

2 or more atoms bond together, they become a mol-

ecule, which is the smallest form of a compound that

still retains the chemical properties of that compound.

For example, a water molecule is formed by 2 hydro-

gen atoms and 1 oxygen atom. In living organisms, mol-

ecules come together to form cells. The human body

is a mosaic of intertwined systems constructed of an

Directed Reading

hig

s t

cloud at the filament a

s t

gy toward the anode. The high-speed elec-

trons, coming from the filament wires of the , are

stopped abruptly at the surface of the anode (see Figure

infrared iat and x-s.4

Target Interactions

The electrons that form the thermionic cloud around

the filament arrive at the anode target traveling at nearly

Figure 1. X-ra

be components. © ASRT 2021.

Scattered x-ray

Incident x-ray photon

Atom

ctron

Scattered x-ray

ized

K-

Projectile

electron

Angle

of deection

FIG 6

FIG 3

electron

Incident

λ < λ’

λ’

yIonized

K-shell

electron

Ionized

K-shell

electron

Projectile

electron

Characteristic

x-ray

Characteristic x-ray

Projectile

electron

Heated lament

emits by

Heated lament

emits electrons by

thermionic emission

Electrons are

accelerated by a high voltage

Electrons are

accelerated by a high voltage

X-

X-rays produced when

high speed electrons

hit the metal target

Copper rod for

heat dissipation

Filament and

electron cloud

Focal spot on

target

Glass envelope

Copper

stem

(+)

Tube window

Cathode (-)

Focusing

cup

Useful x-

e-+

e-Copper rod for

heat dissipation

Scattered x-ray photon

Electron

Incident x-ray photon

Atom

Projectile

electron

Low energy

bremsstrahlung x-ray

Photoelectron

Incident

x-ray

Scattered x-ray

Ionized

K-shell electron

Projectile

electron

Angle

of deection

FIG 6

FIG 3

Compton

electron

Incident

x-ray

λ < λ’

λ’

Projectile

electron Characteristic

x-rayIonized

K-shell

electron

Ionized

K-shell

electron

Projectile

electron

Characteristic

x-ray

Characteristic x-ray

Projectile

electron

High energy

bremsstrahlung x-ray

Heated lament

emits electrons by

thermionic emission

Heated lament

emits electrons by

thermionic emission

Electrons are

accelerated by a high voltage

Electrons are

accelerated by a high voltage

X-rays produced when

high speed electrons

hit the metal target

X-rays produced when

high speed electrons

hit the metal target

Copper rod for

heat dissipation

Filament and

electron cloud

Focal spot on

tungsten target

Glass envelope

Vacuum

Copper

stem

Anode (+)

Tube window

Cathode (-)

Focusing

cup

Useful x-

e-+

e-Copper rod for

heat dissipation

t are called inci-

dent elec

ns and are represented in drawings as a solid

arrow, whereas x-s are represented by a wavy arrow.2

tions and ch

acteristic interactions.

Bremsstrahlung x-

. Because the nucleus has a positive

charge and the electron has a negative charge, an attrac-

tion occurs. The electron cannot penetrate the nucleus

and therefore is forced to slow down and change direc-

tion. As the electron slows and changes course, it loses

energy in the form of a bremsstrahlung x-

ton.

The energy of a bremsstrahlung x-ray photon is the dif-

ference between the entering and exiting kinetic ener-

gy of the electron. The amount of kinetic energy lost by

the incident electron in a bremsstrahlung interaction is

determined by the electron’s distance from the nucleus.2

At larger distances, little kinetic energy is lost, result-

ing in a low-energy bremsstrahlung x-ray. At smaller

distances, more energy is lost, resulting in high-energy

bremsstrahlung rad

(see Figure 3).2 The energy of

a bremsstrahlung x-ray is unpredictable. It can

be as h

inimal that it

is nearly immeasurable.2

rget

atom. The incident electron will knock out the K-shell

electron, izing the atom and creating a hole, which

makes the atom unstable. An electron from an outer shell

(ie, L-shell, M-shell, N-shell, and so forth) drops in to fill

the hole and loses energy in a process known as charac-

teristic cascade because a higher-energy electron drops

into a lower-energy hole.2 This process continues until

the outermost shell is missing an electron. The amount

of energy that the electron loses is the difference between

the binding energy of the outer and inner shells between

which it dropped. The energy lost is known as a

.2 For a diagnostic c

ton to be produced from this interaction, t

K-

t needs to be ejected with e

tron drops

Figure 2.

ssion. The electrons then are accelerated by

a high voltage an

nod

t. © ASRT 2021.

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Biological Effects of

travels through space as a combination of electric and

magnetic fields. There are many forms of electromag-

netic energy, including2:

cosmic rays

infrared light

microwaves

radio waves

visible light

between shells L and K, M and K, N and K, and so on.

m (see Figure 4).

- Beam

Electromagnetic energy is a state of energy that sur-

rounds everything constantly.4 Electromagnetic energy

Figure 4. Characteristic x-ray photons are

rget atom. © ASRT 2021.

Scattered x-ray

Incident x-ray photon

Atom

ctron

Scattered x-ray

ized

K-

Projectile

electron

Angle

of deection

FIG 6

FIG 3

electron

Incident

λ < λ’

λ’

yIonized

K-shell

electron

Ionized

K-shell

electron

Projectile

electron

Characteristic

x-ray

Characteristic x-ray

Projectile

electron

Heated lament

emits by

Heated lament

emits electrons by

thermionic emission

Electrons are

accelerated by a high voltage

Electrons are

accelerated by a high voltage

X-

X-rays produced when

high speed electrons

hit the metal target

Copper rod for

heat dissipation

Filament and

electron cloud

Focal spot on

target

Glass envelope

Copper

stem

(+)

Tube window

Cathode (-)

Focusing

cup

Useful x-

e-+

e-Copper rod for

heat dissipation

Scattered x-ray photon

Electron

Incident x-ray photon

Atom

Projectile

electron

Low energy

bremsstrahlung x-ray

Photoelectron

Incident

x-ray

Scattered x-ray

Ionized

K-

shell electron

Projectile

electron

Angle

of deection

FIG 6

FIG 3

Compton

electron

Incident

x-ray

λ < λ’

λ’

Projectile

electron Characteristic

x-rayIonized

K-shell

electron

Ionized

K-shell

electron

Projectile

electron

Characteristic

x-ray

Characteristic x-ray

Projectile

electron

High energy

bremsstrahlung x-ray

Heated lament

emits electrons by

thermionic emission

Heated lament

emits electrons by

thermionic emission

Electrons are

accelerated by a high voltage

Electrons are

accelerated by a high voltage

X-rays produced when

high speed electrons

hit the metal target

X-rays produced when

high speed electrons

hit the metal target

Copper rod for

heat dissipation

Filament and

electron cloud

Focal spot on

tungsten target

Glass envelope

Vacuum

Copper

stem

Anode (+)

Tube window

Cathode (-)

Focusing

cup

Useful x-ray beam

e-+

e-Copper rod for

heat dissipation

Figure 3. The e

e because it can be as

nimal that it is

nearly immeasurable. © ASRT 2021.

Directed Reading

Characteristics of ionizing radiation include charge,

mass, and energy.1 These attributes, which vary among

different types of radiation, determine the extent to

which energy is transferred into tissues. Three concepts

associated with how ionizing radiation causes injury

and how its effects can vary in tissues are linear ener-

gy transfer (LET), relative biological effectiveness, and

oxygen enhancement ratio.

LET can be described as a measurement of the rate

in which energy is transplanted from ionizing radia-

tion to the body’s soft tissues.4 Because the amount of

ionization produced in an irradiated object is related to

the amount of energy it absorbs and because chemical

and biological effects in tissue coincide with the degree

of ionization experienced by the tissue, the LET value

of radiation involved is an important factor in assess-

ing potential tissue and organ damage from exposure

to that type of ionizing radiation.1 Ionizing radiation

received from x-rays and gamma rays is low-LET radi-

ation. Examples of high-LET radiation are alpha par-

ticles and s of heavy nuclei. Internal contamination

from a

l that has been implanted, ingested,

injected, or inhaled is of great concern with high-LET

diation.1

As the LET of radiation increases, its ability to

produce biological damage also increases.4 Identical

doses of radiation with different LETs, such as diag-

nostic x-rays (LET 5 3.0) vs 5 MeV alpha particles

(LET 5 100.0), do not deliver the same biological

effect. This effect

fect

a particles is

20. A

ss. H

n individual.

rradiated in an ox

ated, or aerobic state,

biological tissue is more sensitive to radiation than

when it is exposed to radiation under anoxic (without

) or hypoxic (low ox

) conditions. This is

known as the oxygen effec

io describes this effect numericall

io compares the biological response

of cells to radiation when those cells are without

ic energ

.2 Only an extremely small segment of t

ic energy conti

m—the vis

ight seg-

ment—is naturally apparent to the human eye. The

ancient eks called an atom of light a

, and

although there are many types of electromagnetic ener-

gy, the term

still is used when referring to an

x-ray. A photon is sometimes pictured as a small bun-

dle of energy that travels through space at the speed of

light.4 Scientists have discovered that electromagnetic

radiation can behave as a particle or as a wave. This du

y of radiation.

To best understand x-

gy.2

s. Mechanical waves are caused by

disturbances in a medium.2 Examples of mechani-

cal waves include ocean waves with water being the

medium and sound waves with air being the medium.

Electromagnetic waves do not require a medium; there-

fore, they can travel through space. All types of s

wave. Ele

. The important properties of the sine wave model

are frequency and wavelength.4 The wavelength is the

distance from 1 crest to another, from 1 valley to anoth-

er, or from any point on the sine wave to the next cor-

responding point.4 Wavelength is represented by the

Greek letter lambda (λ). The frequency is the number

of waves that pass a particular point in a given period

(eg, number of cycles per second) and is represented by

the Greek letter nu (υ).2 The relationship among veloc-

ity, frequency, and wavelength is important because a

change in 1 parameter affects the value of the others.

Velocity is constant at the speed of light (c); therefore, at

a given velocity, wavelength and frequency are inversely

proportional.4 The following equation is used to calcu-

late wavelength and frequency4:

c 5 υ λ

Directed Reading

Biological Effects of

energy retained by the scattered x- depends on the

energy of the original x-ray and the angle of deflect

from the Compton ct

.2 The higher the energy of

the original x-ray, the higher the energy the scattered

photon has. Scattered x-ray photons can be deflected at

any angle. If there is no deflection, the scattered x-ray

does not lose energy. The greater the deflection from

the Compton electron, the less energy the scattered

x-ray has. Most x-s scatter in a forward direction

toward the image receptor.

iat

and i

mary reason for wearing protective devices, such as d

, and for providing protective shield-

ing for the x-ray room.2

As an incident x-ray interacts with an inner-

shell electron of an a in the body, ejecting that elec-

tron from its shell, the x-ray loses all of its energy and

is absorbed. This process is called the

t (see Figure 6).4 The ejected electron is known

as a photoelectron. Because there is a hole in the inner

shell, t

s from the outer shells drop into the hole.

This electron transition is accompanied by the emis-

sion of an x- whose energy is equal to the difference

between binding energies of the shells involved. These

characteristic x-s consist of secondary rad

and

behave in the same manner as scattered r

iation.4

These x-rays are of very low energy and do not reach the

image receptor or are absorbed.

Cell

Radiation-induced damage occurs at the ic

level when an x-ray interacts with an atom. This

interaction results in i

xcit

ith the biological response of cells when they

are in a typical ox

ated state. Without oxygen, a

cell can repair itself. In an oxygenated state, however,

the cell might be damaged to a point where it cannot

be repaired.4

As R researched x-, he identified numer-

ous properties that illustrate why they are harmful to

human tissue. For example, x-

ic iat with many energies

and waveleng

hs. They are able to

n occurs. 2

Interactions with Matter

When an x-m passes through matter, such

as the body, it undergoes a process called at

ion.

Attenuation is the reduction in the number of x-ray

photons in the beam and the subsequent loss of energy

as the beam passes through mat

-rays t

throug

mage

that re

es t

ptor or is absorbed by someone other

than the patient. The 2 most prevalent interactions with

mat

iat a

atter and tric effect.

During at

ing, the incident x-ray pho-

ton interacts with a loosely bound outer shell t

of an in the body. The loosely bound electron is

ejected from its shell and is known as a Compton (recoil)

electron.2 The incident x-ray photon continues in a dif-

ferent direction with less energy and now is known as

a scattered x-ray photon (see Figure 5). The amount of

Figure 5.

. © ASRT 2021. Figure 6. Photoelectric effect. © ASRT 2021.

Scattered x-

Incident x-ray photon

Atom

ctron

Scattered x-ray

ized

K-

Projectile

electron

Angle

of deection

FIG 6

FIG 3

electron

Incident

λ < λ’

λ’

yIonized

K-shell

electron

Ionized

K-shell

electron

Projectile

electron

Characteristic

x-ray

Characteristic x-ray

Projectile

electron

Heated lament

emits by

Heated lament

emits electrons by

thermionic emission

Electrons are

accelerated by a high voltage

Electrons are

accelerated by a high voltage

X-

X-rays produced when

high speed electrons

hit the metal target

Copper rod for

heat dissipation

Filament and

electron cloud

Focal spot on

target

Glass envelope

Copper

stem

(+)

Tube window

Cathode (-)

Focusing

cup

Useful x-

e-+

e-Copper rod for

heat dissipation

Scattered x-ray photon

Electron

Incident x-ray photon

Atom

Projectile

electron

Low energy

bremsstrahlung x-ray

Photoelectron

Incident

x-ray

Scattered x-ray

Ionized

K-shell electron

Projectile

electron

Angle

of deection

FIG 6

FIG 3

Compton

electron

Incident

x-ray

λ < λ’

λ’

Projectile

electron Characteristic

x-rayIonized

K-shell

electron

Ionized

K-shell

electron

Projectile

electron

Characteristic

x-ray

Characteristic x-ray

Projectile

electron

High energy

bremsstrahlung x-ray

Heated lament

emits electrons by

thermionic emission

Heated lament

emits electrons by

thermionic emission

Electrons are

accelerated by a high voltage

Electrons are

accelerated by a high voltage

X-rays produced when

high speed electrons

hit the metal target

X-rays produced when

high speed electrons

hit the metal target

Copper rod for

heat dissipation

Filament and

electron cloud

Focal spot on

tungsten target

Glass envelope

Vacuum

Copper

stem

Anode (+)

Tube window

Cathode (-)

Focusing

cup

Useful x-ray beam

e-+

e-Copper rod for

heat dissipation

Directed Reading

radiosensitive. Conversely, mature cells are radioresis-

tant.4 In diagnostic imaging, this law serves to remind

radiologic technologists that fetuses and children are

considerably more sensitive to radiation exposure than

are adults.4

Various quantities, units, and radiation dosimetry

concepts have been developed and defined to quanti-

fy the amount of radiation received by individuals. In

1948, the I

Measures was charged with developing an international

system of units based on the metric system. The com-

mittee developed the International System of Units, or

SI units.2 Diagnostic imaging professionals must have a

clear understanding of the following radiation quanti-

ties and their corresponding SI units1:

absorbed dose (gray [Gy])

air kinetic energy release in material (ie, air

kerma) (Gy)

effective dose (sievert [SV])

equivalent dose (Sv)

exposure (coulomb/kilogram [C/kg])

ses through an object, such

as a human body, some of the energy of that rad

ion is

absorbed by the objec

that the patient absorbs per

unit mass. This absorbed energy can cause damage in

biological tissues.1

Air kerma is used to express how energy is trans-

ferred from a beam of radiation to a material such as the

patient’s ski

n radiographic and fluoroscopic

units incorporate the entire amount of energy delivered

to the patient by the x-am, which is referred to as

the d

ct.1 Dose a

t refers to the

total amount of radiant energy that has been delivered

to the patient.1 Whereas, ai

ma refers to the amount

of radiation delivered to a specific defined position such

as a point on the patient’s sk

ionizing radiation. Effective

dose incorporates the effect of the type of iat

hting factors.

electrons of the atom and a transfer of energy to the sur-

rounding tissue.4 The molecular composition of a tis-

sue determines the extent of radiation damage that can

occur because certain cells in the body are more radio-

sensitive. Reproductive cells and lymphocytes regen-

erate often, making them more sensitive to radiation.

Muscle and nerve cells regenerate slowly, resulting in

less sensitivity.

The

n can change its binding

properties to other at

, especially if the atom is a

component of a large molecule. Ionization can cause the

molecule to break or an atom to change positions in the

molecule. This causes the irregular molecule to func-

tion improperly, not function at all, or kills the cell.4

However, this process can be reversed. Atoms that have

been ionized can become neutral again by attracting

free e

. In that event,

ion.4

Radiation-induced damage at the cellular level can

damage somatic cells, only affecting the person receiv-

ing the radiation, and reproductive cells, potentially

resulting in the damage being passed on to future gen-

erations. If a large number of cells are affected, the

whole body can be affected.1

The effect of radiation interacting with a cell is clas-

sified as direct or indirect. A direct interaction occurs

when ionizing radiation interacts with essential mol-

ecules. I

t interactions occur when t

adical. Fre

icals are unstable and

can interact with other molecules. They have the capac-

ity to cause serious damage to DNA, which can cause

cell death.1 Approximately 80% of a cell is composed

of water, so most of the interactions that happen in the

body in the low-LET range (eg, x-s) are indirect.1

In 1906, French radiologist

iè and

French physician L

ved

and theorized that

itivity was a function

of the metabolic state of the tissue being irradiated.4

Their findings eventually became known as the law of

Bergoniè and Tribondeau, which states that the radio-

sensitivity of living tissue varies with tissue maturation

and metabolism.1 A high growth rate in cells and tis-

sues results in radiosensitivity. Stem cells and younger

tissue and organs have high metabolic activity and are

Directed Reading

Biological Effects of Radiation Exposure

decrease in the radiation level as a consequence of the

dispersion or spread of the radiation beam, imaging

personnel receive less radiation exposure by standing

farther away from a source of radiation.1 The inverse-

square law states that the intensity of the radiation

beam is inversely proportional to the square of the dis-

tance from the source.1 This law expresses the relation-

ship between distance and the intensity (quantity) of

radiation and governs the dose received by personnel.

Mathematically, the

uar is written as:1

I1 (D2)2 5 I2 (D1

where I1 is the exposure (intensity) at the original dis-

tance, and I2 is the exposure (intensity) at the new dis-

tance. D1 is the original distance from the source of

iat, and D2 is the new distance from the source of

ion.

Types of Injury

ldren. These negative

effects can occur immediately after exposure, or they

might take years to appear. The probability and severity

of these effects depend on the dose administered.

Somatic effects are radiation effects that are suffered

by the exposed individual. These types of reactions

might come on quickly, although some do not show up

for quite some time. These radiation effects can affect

an exposed individual for their lifetime. It might take

only minutes to detect the killing of cells in the affect-

ed area, whereas scarring and tissue breakdown could

take longer.5 Examples of somatic radiation effects that

correlate with dosages are listed in the Table.5,6 If treat-

ment is delayed, somatic effects could result in the

development of tumors or cancer.7

Developing fetal tissues are susceptible to seri-

ous harm. The central nervous system is most affect-

ed, with the possibility of causing mental retardation,

chromosomal damage, or congenital defects.7 X-ray

nant mother must be limited, as

well as to children. In 2008, a child aged 23 months

who was undergoing a CT examination was over-

exposed during the 65-minute scan. This caused

The term that specifically considers the relative detri-

ment to each particular organ and tissue is called the tis-

sue weighting factor (WT

).1

tor (WR). The

radiation weighting factor takes into account that some

types of radiation are more efficient at causing biologi-

cal damage for a given dose than are other types of radi-

ation. Equivalent dose is used for r

ng radi

ion.1

Exposure is a radiation quantity that expresses the

intensity of radiation delivered to a specific area, such as

the surface of the human body. It is based on a response

produced when radiation interacts with air.

To offset possible damage from

ly, 0.5 mSv; entire gestation, 5.0 mSv)

The National Council on Radiation Protection and

Measurements defines frequent as those who are

exposed continuously. Infrequent refers to a justi-

fied exposure that is not likely to occur often in a

person’s lifetime.

Radiation Safety Principles

Three principles of radiation safety are time, dis-

tance, and shielding. These principles can be used

to reduce occupational and patient radiation expo-

ati

posi

ing ma

ial, which attenuates t

ation from the source.2

Distance is the most effective means of protection

from

ion. Because there is a substantial

Directed Reading

Walker, Watts

diaster.10 A fetal radiation dose of 1 Gy (1000 mSv) will

cause mental retardation in approximately 75% of fetus-

es with gestational ages 8 to 15 weeks.

o called early ef

or deterministic ef

ts, are those ef

ts where the

incidence and severity of the ef

t increases with

increasing dose, but for which there is a threshold

dose.9 The severity of harm depends on the dose. An

example of a nonstochastic effect would be an infant

receiving r

ns after continuous rad

to the same area of the body. Nonstochastic effects

include acute radiation sickness and chronic radia-

tion sickness. Ac

iation has been given in a short peri-

od. These patients develop radiation effects quick-

ly. Chronic radiation sickness takes a little longer,

possibly months, and these patients develop long-

term radiation effects. Examples of chronic radia-

tion sickness are cataracts or infertility. These effects

are based on the size of the dose and typically occur

at high doses of radiation, which can be avoided

completely.

Acute Sickness

adiation sickness (ARS), also known as

acute radiation syndrome or toxicity, is caused by

high doses of radiation delivered in a short period.

Individuals can acquire ARS if most of the body was

exposed; radiation dose was high; radiation reached

internal organs; or radiation was given in a short

span.11 Symptoms can start immediately after ex

and might last for minutes to days, with the symptoms

coming and going for a period.

Treatment for ARS includes staying hydrated;

receiving supportive care; treating infections with anti-

biotics, antivirals, or antifungals; and treating injuries

such as radiation burns. Some patients might need more

specialized, invasive treatments such as granulocyte-

colony stimulating factor, which helps stimulate the

production of white blood cells and bone marrow.10

According to the National Organization for Rare

Disorders (NORD), the 3 types of ARS are hema-

topoietic sickness or bone marrow sickness, gastro-

intestinal sickness, and cardiovascular and central

nervous system sickness.11,12

radiation burns under his eyes and on the bottom half

of his face. Later, a blood sample from the child was

analyzed and revealed serious chromosomal damage

from radiation exposure.8

Genetic effects are caused by radiation-induced

mutations to the male or female reproductive cells,

causing DNA damage that can be transmitted to the

next generation. Some of these effects, such as heart

defects, cleft palate, or microcephaly, might not become

apparent for several generations.

nchastic

Stochastic effects, or late effects, are related to the

probability of the effect occurring after radiation expo-

sure and depends on the dose. The probability of an

effect occurring increases with increasing dose, but

there is not a specific threshold dose.9 There are no

risk-free doses, and in some cases, these effects cannot

be completely avoided because they are considered to

occur by chance. If harm occurs, it usually occurs years

after the exposure. An example of a stochastic effect

would be the development of cancer years after expo-

sure. The amount of radiation determines the probabil-

ity of effect. For example, consider the radiation effects

that were suffered by many people from the C

dis

0 mSv. This is equivalent to 80 000 to 160 000 chest

radiographs.10 The chance of certain cancers, especial-

ly thyroid and breast cancers, significantly increased in

individuals exposed to radiation from the Chernobyl

Table

Examples of S

ffects with

Correlating Dosages5,6

Dosage (Gy) Somatic effects of radiation

2-3 Sunburnlike injuries to the skin with possible

hair loss

. 10

system issues including

nausea, vomiting, or both

. 50 Central nervous system issues including shock,

confusion, and pressure on the brain

Directed Reading

Biological Effects of

brain. Treatment can include a form of sedation medica-

tion to help with pain and convulsions combined with

oxygen therapy.12

Phases

In addition to the 3 types of ARS, there are 4 clini-

cal phases associated with ARS: prodrome, latency,

manifest illness, and final (recovery or death).13,14 The

prodromal phase occurs within hours of exposure and

consists of acute clinical symptoms that can contin-

ue for a couple of days.6 Symptoms in the prodromal

or first stage of acute radiation effects include nausea,

vomiting, fever, and diarrhea. The severity of these

symptoms is dose dependent and devastating if the dose

exceeds 10 Gy.

After the

ient appears well. This period is called the

se, which can occur for hours or up to weeks.6

During this period, there might not be any visible symp-

toms, but internal damage is occurring to the cells. Full

clinical effects of radiation sickness are evident during

the next phase, manifest phase, such as15:

disorientation

hair loss

hypotension

internal changes (eg, decreased lymphocytes, low

platelet count, and increased temperature)

malaise

radiation burns

Survival in the final stage depends on the radiation

dose and other factors, including distribution of the radia-

tion, the individuals’ general health and sensitivity to radi-

ation, and the treatment they received. T

Exposure

The I

Protection uses 3 fundamental principles of radiological

protection18:

justification – the benefits of any alteration to the

radiat

detriments



imi

must be ALARA,

keeping in mind the risks and benefits of radiation

Hematopoietic sickness is a type of ARS that occurs

with doses between 2 to 10 Gy and is characterized by:

decreased number of leukocytes (white blood

cells), erythrocytes (red blood cells), and throm-

bocytes (platelets)

fever

lack or loss of appetite

malaise

nausea

vomiting

In more severe cases, infection and hemorrhage have

been reported. Treatment can include antibiotics for

infection, platelet transfusion, and blood transfusions.12

Gy or greater. It typically is characterized by12:

diarrhea leading to dehydration

fever

imbalance of electrolytes (can lead to seizures,

body twitching, and heart arrhythmias)

infection

intractable nausea

vomiting

Treatment can include an antiemetic (ie, medications to

help with nausea and vomiting), a bland diet, and fluids.12

NORD classifies cardiovascular and central ner-

vous system sickness as a type of ARS produced by

high total-body doses of

(eg, $ 30 Gy).12

This is the most severe of the 3 types of ARS. It is

characterized by11:

anxiety

confusion

convulsions

loss of consciousness

nausea

nervousness

tremors

vomiting

Without treatment, coma and death are possible. A

cause of death can be elevated fluid content in the

Directed Reading

never stand in the primary or useful beam. They

should stand at right angles (90°) from the patient to

avoid

ion. Pregnant individuals should

never assist a patient during exposure to avoid unnec-

essary radiation to the fetus. The e

the portable units must be at least 2 m long. In

hnologists should step behind the con-

trol booth lead ba

rier. Standing 2 m from the patient

during exposure is best and cuts down on the amount

of scatter radiation.23 The xam should never be

pointed toward the radiographer console.

Shielding protection includes:



s for f

f

urtains



t

ields

Wrap-around lead aprons should be worn in radiog-

raphy, f

, and in surgical cases. A lead apron

should be included with every portable x-ray unit.

Leaded eyewear can reduce e

he eyes from

backscatter by up to 90% in certain surgical cases. Use

of protective eyewear is common in interventional radi-

ography and is becoming more common in orthope-

dics.3,24 Lead shields can be transparent acrylic or glass;

both contain 30% lead by weight and can absorb up to

90% of scatter radiation. These types of shields can be

suspended from the ceiling, portable on wheels, placed

into a lead-lined frame, or be used in barriers, windows,

and doors.24

Imaging personnel who are exposed to ionizing

radiation should be supplied with personal monitor-

ing devices so that the amount of radiation they receive

can be monitored. These individuals typically are given

1 personal monitoring device to measure the amount

of radiation ex

re received. These dosimeters help

ensure that workers are receiving a safe amount of radi-

ation in a certain period. R

gainst radiation; they only monitor the

radiation the individual receives.24,25

exposure and optimizing sources of rad

ion

protection.

 limitation – individual dose from a planned

exposure should not exceed recommendations

According to the International Commission on

s 100 mSv.

International Commission on Radiological Protection

recommends less than 1.0 mSv total fetal exposure dur-

ing an entire pregnancy.17 Dose limits recommended

by the National Council on Radiation Protection and

Measurements for specific tissues and organs are16:

skin – 500 mSv/yr (50 rem/yr)

extremities – 500 mSv/yr (50 rem/yr)

lens of the eye – 150 mSv/yr (15 rem/yr)

A radiologic technologist’s radiation exposure in

diagnostic radiology mostly comes from fluoroscopy

and mobile radiography (95%), but interventional radi-

ology, surgery, mammography and CT also contrib-

ute to exposure. Adhering to A

tion (time, distance, and

shielding) can minimize radiation exposure and protect

iologic technologists.6

Time

ime should be kept at a minimum, and

facilities should have a timer to help limit radiation time

in f

. Technologists must think about options

to decrease rad

maging,

ollimation, and the last-image hold feature.23

Distance

Radiologic technologists should step back when

their immediate assistance is not needed in fluoros-

copy. Increasing distance from the patient decreases

the amount of scat

reaching the i

iat

.6 T

is-

ta of the x- f

mage receptor, the

iat

ity will dec

se.6 If t

iographer

must help hold a patient during ex

re, they should

Directed Reading

LDs are more sensitive and more accurate than are

film badge dosimeters. They can properly measure low

levels of radiation and can be read on site without hav-

ing to be sent out for development. TLDs do not suf-

fer from high temperatures a

option once a TLD is evaluated by the vendor

Optically stimulated luminescence dosimeters are

worn and handled similarly to film badge dosimeters,

but the detector materials are made of aluminum oxide

in a crystal form, which detects the

ia-

tion. Optically stimulated luminescence dosimeters

can report lower doses than can TLDs and film badge

dosimeters and are more accurate.22,24However, optical-

ly stimulated luminescence dosimeters are more expen-

sive than are TLDs and film badge dosimeters. Their

validity can be questioned with very low doses, and

they are sensitive to light.

ALARA means making every reasonable effort to

keep radiation doses low while still obtaining high-

quality images. The benefits of imaging-related radi-

ation exposure should outweigh the risks.26 The 3

principles of ti

ielding should be fol-

lowed to limit radiation exposure. Additional methods

that radiologic technologists can use to reduce radiation

dose to the patient include6,27,28:

Avoid unnecessary examinations. Benefits of an

examination must compensate for radiation dose

to the patient.

Know the correct technical factors so that

patients receive the proper amount of radiation

dose for the examination ordered.

Maintain quality control and quality assurance

to ensure that equipment is working properly and

not delivering unnecessary radiation.

Minimize repeat imaging by consistently provid-

ing high-quality diagnostic examinations.

Perform f

mitt

ly, keeping

x- on for only a few seconds at a t

nant,

she should notify her supervisor so that a fetal dose

monitoring device can be provided. This monitoring

device should be worn under a lead apron at waist level.

Film badge dosimeters contain a small piece of film

that is placed between metal filters inside a plastic hold-

er. The film emulsion darkens in proportion to the

amount of radiation that strikes the film.22 To accurately

measure the amount of radiation to which a technolo-

gist is exposed, the film badge dosimeter must be care-

fully calibrated, processed, and analyzed.12 Dosimeters

should be worn with the correct side in the front to pro-

vide accurate readings. For fluoroscopy, CT, and radi-

ography, the dosimeter should be worn at the collar

level. For a pregnant radiographer, an additional dosim-

eter should be worn at the waist level. The badges are

usually kept by the vendor as a permanent record of

h individual.25 If only minimal

iation ex

res are acquired, then the film badge

vendor assigns an “M” for that time frame to denote a

nimum dose was given. When high doses are report-

ed, an investigation is necessary to see why the dose

level was high for that individu

0s.24

However, they cannot be reused, should not be worn

for longer than a month, should not be left in the car

where high temperatures can occur, and are sensitive

to moisture.

hermoluminescent dosimeter (TLD) monitor

is made up of lithium fluoride crystal that absorbs the

x- energy to measure iation dose. When phosphor

materials in the TLD are exposed to ionizing radiation,

some of the electrons in the phosphors become excit-

ed, and when the TLD is evaluated, the excited elec-

trons are released as light. The radiation dose received

by the TLD is measured based on the amount of light.24

TLDs are available as a badge, a bracelet, and a ring.

The bracelet and ring dosimeters are designed for peo-

ple who work in a setting where their hands and fingers

come into direct contact with radiation.

Directed Reading

way to achieve this is by increasing kV

reasing

mAs). During an e

is the maximum potential (ie, voltage) applied to the

.4 The unit of electric current is the ampere

(A), and the number of x-s produced are measured in

milliamperes (mA). T

ing the mAs. When kVp increas-

es, the penetration of the x-

am increases and can

cause less radiation absorption by the patient.6

he -

ntar

lizat

niq such as9:

radiolucent posit

ing sponges

sandbags

sheets and towels

tape

hook-and-loop closure straps

Involuntary motion includes things like breathing

motion, medication-induced movement, and movement

from disorders like Parkinson disease or restless leg

syndrome. Shorter exposure times and performing the

procedure correctly the first time can help reduce invol-

untary motion.

Communication between the radiologic technologist

and the patient is key. Establishing good rapport helps

patients feel more comfortable and cooperate more

effectively. Providing the patient with clear instruc-

tions, such as “take in a breath and hold it,” also helps

avoid the need for repeat imaging.

Conclusion

Radiologic science is a growing field that is focused

on attaining high-quality diagnostic images. It is impor-

tant to remember the 3 cardinal rules for technologists:

time, distance, and shielding. These rules not only protect

the technologist from

but also patients. Finding

creative ways to limit the number of repeat ex

res

and knowing precise technical factors are fundamental.

Use proper

e ter

Use last image hold and electronic collimation.

Last image hold digitally freezes an image on the

monitor, allowing the radiologist to study the

image and make their next move without radia-

tion exposure. Electronic collimation overlays a

collimator blade on the last image hold so that the

technologist can adjust field dimensions without

exposing the patient.

To ensure examinations are performed correctly the

first time, technologists must use proper patient posi-

tioning and optimal patient exposure, know when and

how to be creative with positioning if standard position-

ing cannot be achieved, and communicate effectively

with patients so that they understand instructions.23,29

Before reaching the patient, low-energy x-

he x-

s and increase the average energy of the x-

m.6 Filters help produce a cleaner image by absorb-

ing the low-energy x-rays that typically produce more

scatter.

Limiting the size of the beam through collimation

reduces

er.23 Beam collimators are lead

shutters that absorb photons. This helps focus the radi-

ation to the desired area and limits the radiation dose

to anatomy that is not of interest. Positive beam limita-

tion is 1 tool that can be used to reduce undercollima-

tion (ie, the inappropriate use of large radiation fields).

It is an automatic adjustment of the x-am matched

to the size of the image receptor. With this feature, the

radiographer cannot open the collimators beyond the

image receptor size, which prevents unnecessary radia-

tion to the patient.

and Low Milliampere Second

Technique

Radiologic technologists should optimize technical

factors to reduce patient dose as much as possible. One

Directed Reading

Biological Effects Exposure

9. Seeram E.

: Physical Principles,

Clinical Applications, and Quality Control. 4th ed. Elsevier;

2016:202-231.

10. López M, Martin M. Medical management of the acute

yndrome. Rep Prac Oncol Radiother. 2011; 16:138-

146. doi:10.1016/j.rpor.2011.05.001

11.

yndrome (ARS): a fact sheet for the public.

. Reviewed April

4, 2018. Accessed April 18, 2020. https://www.cdc.gov

/nceh/radiation/emergencies/ars.htm

12. Radiation sickness. National Organization for Rare

Disorders. Published 2011. Accessed April 18, 2020.

https://rarediseases.org/rare-diseases/ra-sickness/

13. Garau M, Calduch AL, López EC. Radiobiology

yndrome. Rep Pract Oncol Radiother. 2011;

16(4):123-130.

14.

. In: Chemistry. R

University; chap 21. Accessed April 18, 2020.

https://opentextbc.ca/chemistry/chapter/21-6-biological

-effects-of-/

15. Fosbinder R, Orth D. Essentials of Radiologic Science.

Lippincott Williams & Wilkins; 2012:286-333.

16. Recent applications of the NCRP public dose limit recom-

mendation for ionizing radiation. National Council on

. Accessed April 19,

2020. https://ncrponline.org/wp-content/themes/ncrp

/PDFs/Statement_10.pdf

17.

(ICRP) guidance for occupational exposure. R

Emergency Medical Management. Updated August 9, 2021.

Accessed April 19, 2020. https://remm.hhs.gov/ICRP

_guidelines.htm

18. Menzel HG, Harrison J. E

quan

ty. Ann ICRP. 2012; 41(3-4):117-123.

doi:10.1016/j.icrp.2012.06.022

19. Rehani MM. C

f Patients

for the 21st Century. Am J R

. 2013; 200:762-764.

doi:10.2214/AJR.12.10244

20. Geleijns J, Broerse JJ, Brugmans MJP. He

iology.

pl.

2004;Suppl 14:S19-S27. doi:10.1007/s10406-004-0004-6

21. Malone J, Zolzer F. Pragmatic ethical basis for radiation

protection in diagnostic radiology. BJR. 2016; 89(1059):1-11.

doi:10.1259/bjr.20150713

Technologists have an ethical standard of care to provide

ient radiation exposure.

Jennifer Walker, MSEd, R.T.(R)(CT)(MR), is assistant

professor and CT/MR imaging program director for

in Carbondale, I

. She

currently is a doctoral student in educational administration

and higher education and can be reached at je

siu.edu.

Sandi Watts, MHA, R.T.(R), is associate professor

and radiography program director for Southern Illinois

University in Carbondale, Illinois.

Reprint requests may be mailed to the American Society

of Radiologic Technologists, Publications Department,

15000 Central Ave SE, Albuquerque, NM 87123-3909, or

emailed to publications@asrt.org.

References

1. Statkiewicz SM, Visconti P, Ritenour E, Haynes K.

. 8th ed.

Elsevier; 2018.

2. Carlton R, Adler A, Balac V. Principles of Radiographic

Imaging: An Art and a Science. 6th ed. Cengage; 2018.

3. Kaplan D, Patel J, Liporace F, Yoon R. Intraoperative radia-

tion safety in orthopaedics: a review of the ALARA (As low

as reasonably achievable) principle. BioMed Central. 2016;

10:27. doi:10.1186/s13037-016-0115-8

4. Bushong S. Radiologic Science for Technologists. 11th ed.

Elsevier; 2017.

5. Effects on organs of the body. Br

. Accessed April 18,

2020. https://www.britannica.com/science/

/Ef-

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. Radiologic Science for Technologists: Physics,

Biology, and Protection. 10th ed. Elsevier; 2013:487-536.

7. Somatic and genetic damage caused by rad

. Sciencing.

Accessed April 18, 2020. https://sciencing.com

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8. Domino D. California RT gives deposition in CT overdose

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ublished December 10, 2009. Accessed

January 11, 2021. https://www.auntminnie.com/index.aspx

?sec5ser&sub5def&pag5dis&ItemID588757

Directed Reading

22. Bradley LA. R

iologic technologists.

Technol. 2012; 83(5):447-461.

23. Koth J, Hess Smith M. Radiation safety compliance. Radiol

Technol. 2016; 87(5):511-524.

24. Rumanek J, Kudlas M. Rad

itoring devices. Radiol

Technol. 2019; 91(2):202-204.

25. Dosimeter & and rad

measurement services. Landauer.

Accessed April 20, 2020. https://www.landauer.com

/dosimeter-badges

26. Dewar C. Occupational ra

y. Radiol Technol.

2013; 84(5):467-486.

27.

e reduction techniques. University of Florida. Accessed

April 25, 2020. https://xray.ufl.edu/files/2008/06/Dose

-Reduction-Techniques1.pdf

28. Roberts BW. Patient-centered R

y. Radiol

Technol. 2017; 88(5): 499-514.

29. Tugwell J, Everton C, Kingma A, et al. Increasing source to

image distance for AP pelvis imaging – impact on r

nd image quality.

2014; 20(4):351-355.

https://doi.org/10.1016/j.radi.2014.05.012

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patients undergoing conventional radiological examinations:

is there a cause for concern? Jentashapir J Cell Mol Biol. 2016;

7(2):e31170. doi:10.17795/jjhr-31170

Directed Reading Quiz

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Read the preceding Directed Reading and choose the answer that is most correct based on the article.

1.5 Category A credits

Expires March 1, 2025

Biological Effects of

1. As x-

path. is creates _______.

s, an

b. s, an elect

c. s, an

, a photon

2. e simplest form of an element that retains that

element’s chemical properties is known as:

a. an atom.

b. a molecule.

c. an .

d. a compound.

3. e _______ consists of the lament wires, a

focusing cup, and associated wiring.

a. a

c. target area

d. primary thermal conductor

4. What type of x-

’s nucleus?

a. characteristic

b. nondiagnostic

d. b

5. A _______ is sometimes pictured as a small

bundle of energy that travels through space at the

speed of light.

a. proton

c. electron

d. neutron

6. Which of the following is an example of low–li

ation?

a. of heavy

b. a

ides

7. e amount of energy retained by a scaered x-

depends on:

1. the energy of the original x-ray.

ime.

3. the angle of deection.

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2, and 3

Directed Reading Quiz

8. _______

actor.

b. Eective dose

c. Absorbed dose

9. Five millisieverts is the dose limit recommended by

the

tion and

Measurements for:

a. annual occupational exposure.

b. monthly occupational exposu

ges

d. cumulative exposure to members of the public

who are frequently exposed.

10. Which type

c. pulmonary

ystem

11. Which of t

1. low cost

2. more sensitive and accurate than lm

badge dosimeters

3. can be read on site

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2, and 3

12. Ways to reduce

mation.

2. performing uy intermiently.

3. using the last image hold feature.

a. 1 and 2

b. 1 and 3

c. 2 and 3

d. 1, 2, and 3