Everything You Need to Know About

Radiation Protection

Kelli Haynes, MSRS, RT(R)

Program Director &

Associate Professor

Radiation Protection 45 questions of the 200 will be radiation

protection (22.5%) 10 -Biological Aspects of Radiation 15-Minimizing Patient Exposure 11-Personnel Protection 9-Radiation Exposure and Monitoring

Biological Aspects of Radiation

10 Questions

Cell Radiosensitivity Cells and tissues vary in

their degree of radiosensitivity Immature cells are nonspecialized-

rapid cell division Mature cells are specialized-divide

slower if at all DNA-most radiosensitive part of cell

High Low

LymphocytesSpermatogoniaErythroblastsIntestinal crypt cells

Muscle cellsNerve cellsChondrocytes

Dose Response Relationships

Graphic representation of the relationship between the amount of radiation absorbed (dose) and the amount of damage (response)

Linear or nonlinearThreshold or nonthreshold

Response Response

Dos

e

Dos

e

Linear NonThreshold

LinearThreshold

Response Response

Dos

e

Dos

e

NonLinearThreshold

NonLinearNonthreshold

Relative Tissue Radiosensitivities

LET

RBE

OER

Linear Energy Transfer (LET)

Photons deposit or transfer energy as they travel

The average energy deposited per unit of path length

Assesses potential tissue and organ damage

LET

High-LET Radiation Alpha particles Beta particles

Low-LET Radiation Gamma rays X-rays

Relative Biologic Effectiveness

Measures biologic effectiveness of radiations having different LET’s

Influenced by radiation type, cell or tissue type, physiologic condition, and biologic result

Oxygen Enhancement Ratio

Response to radiation is greater when irradiated in the oxygenated state

Radiation dose required to cause response w/o O2OER= Radiation dose required to cause response w/ O2

Cell Survival and Recovery

LD 50/30Adults-3-4 Gy (300-400 rad)Recovery may occur

Somatic Effects

Biologic damage sustained by living organisms as a consequence of exposure to ionizing radiation

Classified as either early (acute) or late

Short-term vs. Long-term Nausea Fatigue Redness of skin Loss of hair Intestinal disorders Fever Blood disorders Shedding skin

Cancer Embryologic effects (birth defects) Formation of cataracts

Carcinogenesis

The production or origin of cancer

Experiments have shown that radiation induces cancer

Cataractogenesis Cataracts-opacity of the eye lens 2 Gy results in partial or

complete vision loss Threshold, nonlinear

dose-response

relationship

Sterility

Female sterility based on age

of the subject-more radiosensitive

when youngerTemporary sterility-2 Gray (200rad) Permanent sterility-5 Gray (50 rad)

ACUTE RADIATION SYNDROMES

Hematopoietic Syndrome

Whole-body doses ranging from 1 to 10 Gy (100 to 1000 rad)

Reduction of blood cells in circulation results in a loss of the body’s ability to clot blood and fight infection

Gastrointestinal Syndrome

Appears at a threshold dose of approx. 6 Gy (600 rad) and peaks after a dose of 10 Gy (1000 rad)

Without treatment, a dose of 6-10 Gy may cause death in 3-10 days

Cerebrovascular Syndrome

Doses of 50 Gray

(5000rad)

Death within 2 hours

or up to 2 days

Embryonic and Fetal Risks

Fetus is very sensitive

Fetal radiosensitivity

decreases as gestation

progresses

Genetic Effects GSD-used to assess

the impact of gonadal dose Dose equivalent to the

reproductive organs

that would bring genetic

injury to the total population

PHOTON INTERACTIONS WITH MATTER

Coherent Scattering Photon of low energy

interacts with atom. No net energy has

been absorbed by the atom.

Low-energy photons,1-50 kVp

Contributes to fog

Compton Scattering• Moderate energy x-

rays, 60-90 kVp• Interaction with outer

shell electron• Electron ejected,

Atom is ionized• Photon loses energy

and recombines with an atom

• Fog and Scatter

Compton Scattering

FIGURE 2-6 Compton scattering is responsible for most of the scattered radiation produced during a radiologic procedure. (From Radiobiology and radiation protection: Mosby’s radiographic instructional series, St. Louis, 1999, Mosby.)

Photoelectric Absorption Most important interaction

between x-ray photons and the atoms of the pt’s body for producing useful images

Higher energy x-rays (23-150 kVp), more likely to penetrate & not interact

Interaction b/t photon and inner shell electron

X-ray is absorbed Electron ejected

Attenuation

Process that decreases the intensity of the beam

Refers to both absorption and scatter processes

Thickness of body part (mass density) Type of tissue (atomic number)

Minimizing Patient Exposure

15 Questions

Exposure Factors

kVp

mAs

Shielding

Protects gonads when w/i 5 cm of collimated beam

Females receive

more exposure due

to location

of organs

Types of Shields

Flat contact shields

Shadow shieldsShaped contact

shieldsClear lead

Beam Restriction

Purpose-confine useful beam

Reduce scatter

Types Cones Collimators

FiltrationEffect on skin and

organ exposure

Effect on beam energy

NCRP Report #102

The useful beam shall be

limited to the smallest area

practicable and consistent

with the objectives of the

radiological or fluoroscopic examination.

Exposure Reduction

Patient positioning

AECPatient

CommunicationALARA

Image Receptors

Film-screen systemsIntensifying screensDigital Image receptorsCR and DRFilm speed

Image Receptors

Digital CT, CR, DR, DF, NM, MR, & US Photons on a detector Electronic image Matrix Patient dose

Film Intensifying screens convert photons and

expose film Analog image Patient dose

Grids

As grid ratio increases patient dose increases

Increases contrastAbsorbs Compton scatterImproves qualityIncreases patient dose

Fluoroscopy

Pulsed or

IntermittentExposure factorsPositioningFluoroscopy

time

Personnel Protection

11 Questions

Sources of Radiation Exposure (3)

Primary x-ray beamSecondary radiation

1. Scatter

2. Leakage Patient

Basic Methods of Protection

Protective Devices Protective structural shielding

Primary Barriers

Secondary Barriers

Lead Shields

Protective Devices

Aprons

Gloves

Thyroid shields

Protective glasses

Portable (mobile) units

Lead apparelExposure cordStand at right

angles to the

patient

Fluoroscopy

Protective curtainBucky slot coverCumulative timer

NCRP Report #102

Fluoroscopy Exposure Rates General Purpose: 10 R per minute Non-image Intensified: 5 R per minute High Level Control: 20 R per minute

Exposure Switch Guidelines Switch must be of the dead-man type

Radiation Exposure and Monitoring

9 Questions

Units of MeasurementQuantity SI Traditional

Exposure Coulomb/kg roentgen

Absorbed dose gray rad

Dose equivalent sievert rem

Dosimeters

Film Badge

EconomicalPartsMonitors x and

gamma raysTemperature and

humidity can cause fog

Pocket Ionization Chambers

Most sensitiveMust be charged

to zeroAccurate from

0-200 mR

OSL Dosimeter Aluminum oxide

detector Optically stimulated

luminosity occurs when struck by laser light

Accurate reading as low as 1mrem

TLD’s

Look similar to film badge

Lithium fluoride Ionization causes

crystal to change

NCRP #116

Annual occupational

effective dose- 50 mSv

(5rem) Public Exposure- 1 mSv Embryo/fetus exposure-

50 mSv/month Dosimetry records

NCRP #160

Typical effective dose per exam; varies from 0.1 mSv for a chest xray to 1.5 for a lumbar spine

Interventional- ~3mSv CT- range from 2mSv

for a head to 10 mSv for a spine

That’s All Folks!

www.ARRT.org

haynesk@nsula.edu

Review Questions

What is the most radiosensitive part of the cell?

Which is more radiosensitive, immature or mature cells?

This is a picture of what?

Review Questions

What is LET? What is LD 50/30? What is an example of an early somatic

effect? Late somatic effect? What is carcinogenesis?

Review Questions

What is the threshold dose for cataracts? What is the threshold dose for temporary

sterility? What is the threshold dose for

permanent sterility? What is the threshold dose for

cerebrovascular syndrome?

Review Questions

What is the threshold dose for hematopoietic syndrome?

What is the threshold dose for gastrointestinal syndrome?

What are some types of shields? What is filtration? What does NCRP Report # 102 state?

Review Questions

Why do we use a grid? What are the 3 sources of radiation

exposure? What is the SI unit of measurement for

exposure? What is the SI unit of measurement for

absorbed dose?

Review Questions

What is the traditional unit of measurement for dose equivalent?

What is the sensing material in an OSL dosimeter?

What is the sensing material in a TLD dosimeter?

What does NCRP # 116 state?