Radiation Protection Review Film-Screen Combinations Faster

1
Radiation Protection

• Review

2
Objectives

• Learn and/or review basic facts of radiation
  protection.
• Critically think about radiation protection.

3
Responsibility

• The technologist is responsible for protecting
  the patient.
• - Avoid repeating exposures.
• - Use safe exposure factors
  (understanding of technique).
• The radiologist and referring physicians should
  communicate in order to properly care for
  patients and ensure proper exams.
• The benefit must outweigh the risk

4
Ionizing Radiation

• Ionization The ability to remove electrons from
  atoms.
• Results of Ionization Unstable atoms, free
  electrons, low energy x-rays, creation of harmful
  cellular elements, cell death/damage.
• Cell Damage 2 Types
• - Somatic Damage to the exposed
  individual.
• - Genetic Damage to the DNA which may
  be passed on.

5
Sources of Ionizing Radiation

• Natural Background
• The environment
• 82 of human exposure (295 mrem per person)
• Radon 55 (198 mrem)
• Human Body radionuclides in the tissue
  (potassium 40, carbon 14, strontium 90, hydrogen
  3)
• Cosmic rays 30 mrem annually

• Man-Made
• 18 of human exposure to radiation.
• 66 mrem annually
• - 55 mrem imaging
• - 11 mrem consumer products
• - 1 mrem nuclear weapons testing

6
Terms

• Primary Radiation Radiation exiting the tube.
• Exit Radiation X-rays that emerge from the
  patient to produce the image.
• Attenuation Absorption and scatter of the x-ray
  beam as it passes through the patient.
• Heterogeneous Beam X-ray beam that contains
  photons of many different energies.

7
Photon-Tissue Interactions

• The most common interactions are photoelectric
  and compton.
• Photoelectric Associated with photon absorption
  and contrast.
• Compton Associated with scatter.

8
Coherent Scattering
Also referred to as Classical Scattering and
Thompson Scattering. A low energy (10keV)
incident x-ray interacts with a target atom which
then becomes excited and immediately releases
the excess energy in a different direction than
the incident x-ray. The result is a change in
the direction of the x-ray without a change in
energy. Very little coherent scattering occurs
in diagnostic imaging. No ionization occurs.
9
Photoelectric Effect
Results in total absorption of the incident
x-ray. Occurs in the diagnostic range. An
incident x-ray ionizes a k-shell electron. This
results in total absorption of the incident
x-ray and results in an ejected photoelectron.
Characteristic radiation occurs when outer
shell electrons drop to fill the vacancy left by
the ejected electron. These rays act like
scatter. Photoelectric effect equates to the
creation of contrast in the image due to
differential absorption of the incoming photons
in the tissues.
10
Compton Effect
Equates to scatter radiation. Also called
Compton Scattering. An incident x-ray
interacts with an outer shell electron and ejects
it. The x-ray continues in another direction
with less energy. The x-ray traveling in a new
direction offers nothing good to the image and
often results in exposure to others, especially
in fluoroscopy.
11
Pair Production

• Does not occur in diagnostic radiography.
• Produced at photon energies above 1.02 million
  electron volts.
• Involves interaction between incoming x-ray and
  the nucleus.

12
RAD Units

• Quantity Name Symbol
  SI Unit
• Exposure roentgen R
  air kerma (Gya)
• 
  C/kg
• Absorbed Dose rad rad
  gray (Gy1)
• Effective Dose rem rem
  seivert (Sv)
• Radioactivity curie Ci
  becquerel (Bq)
  

13
RAD Units

• Calculating SI units
• R x 0.01 Gy a
• rad x 0.01 Gy 1
• rem x 0.01 Sv
• Ci x 3.7 x10 (10) Bq
• R 2.58 x 10 (- 4) C/kg

14
RAD Units

• Exposure in air 1R 2.58 x 10 (- 4)
• Absorbed Dose The amount absorbed which could
  equate to biologic damage. Rad measures absorbed
  dose. 1gray 100 rad
• Absorbed Dose Equivalent Takes into account
  different biologic effects caused by different
  types of radiation.
• A quality factor is used to express the
  damage of specific
• types of radiation.
• QF takes into account linear energy
  transfer (LET) which equates to
• the damaging effect of radiation as
  it travels through tissue.

15
Quality Factor

• High ionization radiations have a high LET which
  means that they cause more biologic damage.
• Alpha/beta have high LET, while x and gamma rays
  have a low LET.
• QF for x/gamma rays 1
• 100 rads of x-rays 100 rem of x-rays
• QF for neutrons 20, so 100 rads of neutrons
  2000 rem
• X/Gamma rays QF 1 roentgen 1 rad 1 rem

16
Absorbed Dose

• Agencies that set limits
• - NCRP ICRP NRC (enforces standards at
  federal level)
• Effective absorbed dose equivalent The upper
  boundary dose
• that can be absorbed with little risk of
  somatic/genetic damage.
• ALARA Keep exposure minimal.

17
Dose Response
Response
Linear-nonthreshold
Dose
States that no level of exposure is safe, and
that the degree of response is directly related
to the amount of exposure received.
18
Dose Response
Response
Linear-threshold
Dose
States that a dose exists below which a response
does not occur. In other words there is a safe
threshold before which damage will occur. Again,
after that point response is directly
proportional to exposure.
19
Dose Response
Response
Nonlinear-threshold
Dose
States that there is a safe threshold of
exposure, but when exceeded results in responses
that are not directly proportional to the
exposure received.
20
Dose Response
Response
Nonlinear-nonthreshold
Dose
States that no exposure is safe, and that
response is not directly proportional to the
exposure received.
21
Terms

• Stochastic Effects The randomly occurring
  effects of radiation which increase with
  exposure.
• Nonstochastic(Deterministic) Effects Effects
  that become more severe at high levels of
  exposure and do not occur below a certain
  threshold.

22
NCRP Report 116

• The benefits must outweigh the risks when using
  radiation.
• Occupational limit Stochastic effects 5 rem
• Occupational limit Nonstochastic effects Eye
  15rem, Organs 50rem
• Occupational cumulative exposure Age x 1 rem
• Students over 18 5 rem annually
• General public Infrequent exposure 0.5
  Frequent exposure 0.1
• General public Extremities, skin, eyes 5 rem
• Embryo-fetus Total gestation 0.5 rem
• Embryo-fetus Per month 0.05 rem
• Somatic and genetic effects must be kept to a
  minimum!!

23
The Cell

• Three Main Parts 1. Cell Membrane 2. Cytoplasm
  3. Nucleus
• Cell Membrane Protects the cell, holds
  water/nutrients and is semipermeable.
• Cytoplasm Composed mostly of water, Conducts
  cell metabolism, and contains organelles.
• Organelles 1. Centrosomes Participate
  in cell division.
• 2. Ribosomes
  Synthesize protein.
• 3. Lysosomes
  Intracellular digestion.
• 4. Mitochondria
  Produce energy.
• 5. Golgi Apparatus
  Combines proteins carbohydrates.
• 6. Endoplasmic
  Reticulum Moves food/molecules in cell.
• Nucleus Contains DNA and RNA DNA controls
  cell function.

24
Biologic Effects

• As LET rises, so does biologic damage.
• RBE Relative biologic effectiveness Ability
  to produce biologic damage.
• Ionizing radiation can change a cells molecular
  structure, affecting its ability to function
  properly.
• Germ cell exposure can result in mutations being
  passed to the next generation (genetic).

25
Biologic Effects

• Most radiation passes through the body without
  interaction because matter is composed mainly of
  empty space.
• 2 Interactions
• 1. Direct Effect When radiation transfers
  its energy directly to the DNA.
• 2. Indirect Effect When radiation
  transfers its energy to the water in the
  cytoplasm.

26
Direct Effect

• Occurs when radiation transfers its energy
  directly to the DNA or RNA.
• Damage may repair itself.
• Damage may cause mutations that can be passed on.
• Results of the Direct Effect
• 1. No effect most often.
• 2. Alterations to cell function/structure.
• 3. Cell death
• 4. Death of tissues/organs that depend on
  destroyed cells.
• 5. Faulty information passed on resulting
  in cancer etc.

27
Indirect Effect

• Occurs when radiation is deposited into the water
  of the cell.
• Radiolysis of Water Results in ion pair (water
  molecule / free electron)
• - If the ion pair recombines no damage
  occurs.
• - Free radicals may be formed that damage
  the cell, or form hydrogen peroxide in the cell
  which is a poison in the cell.
• Results of Indirect Effect
• 1. No effect Most common response.
• 2. Formation of free radicals.
• 3. Formation of hydrogen peroxide.
• Most damage that occurs to the body is from
  the indirect effect.

28
Radiosensitivity

• Law of Bergonie and Tribondeau Cells are most
  sensitive to radiation when they are immature,
  undifferentiated, and rapidly dividing.
• If cells are more oxygenated, they are more
  susceptible to radiation damage which is known as
  oxygen enhancement ratio.
• As cells mature and become specialized they are
  less sensitive to radiation.
• A whole body dose of 25 rads depresses blood
  count. This is caused by exposure of bone marrow.
  Lymphocytes are the most radiosensitive blood
  cells in the body. Stem cells in bone marrow are
  very sensitive as well.

29
Radiosensitivity

• Epithelial Tissue Lines body and divides
  rapidly making it highly sensitive.
• Muscle Relatively insensitive.
• Adult Nerve Tissue Relatively insensitive as
  well.
• Reproductive Cells Very radiosensitive cells

30
Beam Limitation

• Beam limitation protects the patient by limiting
  the area being irradiated.
• Lead shutters and PBL are used today.
• In the past, cylindrical cones and aperture
  diaphragms were used to limit the beam size.

31
Filtration

• A filter placed between the beam and the patient
  which absorbs low energy (soft) x-rays making the
  overall beam harder (short wavelength, high
  energy).
• Inherent Glass envelope and insulating oil in
  tube.
• Added Aluminum in the path of the beam. The
  mirror.
• Total Filtration The sum of added/inherent
  filtration. Must equal 2.5 mm aluminum
  equivalent.
• Half value layer The amount of filtration
  needed to reduce the intensity of the x-ray beam
  to half its original value.

32
Gonadal Shields

• Gonadal shielding may reduce female gonad dose by
  50, and male gonad dose by 95.
• Types Flat contact shadow shields.

33
Exposure Factors

• Exposure factors determine the quantity and
  quality of the x-rays striking the patient.
• Use the optimum kVp for the part being imaged.
• Use the lowest possible mAs to reduce the amount
  of radiation striking the patient.

34
Film-Screen Combinations

• Faster film-screen combinations reduce exposure
  to the patient because they use less radiation to
  create an image. They have high conversion
  efficiency.
• Slow film-screen combinations use more exposure,
  but create higher detail images.

35
Processing

• Retakes are eliminated by strict quality control
  of all chemical processors.
• Care should be given to gentle handling of film
  and cassettes when loading and unloading.
• Avoid overexposing film to safelight.

36
Grids

• Grids require higher exposure, but may lower
  overall exposure to patient by eliminating
  retakes associated with poor contrast.

37
Repeat Radiographs

• Repeats result in higher patient exposure.
• Repeats should be tracked to understand why
  technologists are repeating and eliminate reasons
  if possible.

38
Technical Standards for Patient Protection

• Minimum source to skin distance for Portables
  12 inches.
• Intermittent fluoroscopy.
• Close collimation.
• Source to tabletop distance for fixed fluoro.
  15 inches or more.
• Source to tabletop distance for portable
  fluoroscopy is not less than 12 inches (15
  preferred).
• Proper filtration.
• 5-minute fluoro timer.
• Limit dose at tabletop to less than 10 R per
  minute (fluoro).

39
Patient Dose Factors

• Measuring patient dose 1. Skin entrance dose 2.
  Mean Marrow dose
• Genetically Significant Dose (GSD) Radiation
  dose that, if received by the entire population,
  would cause the same genetic injury.
• Observe the 10-day rule. X-rays should be
  performed during the first ten days following the
  onset of menstruation. The 10-day rule is based
  on the fact that most females are not pregnant
  during that time.
• Radiation doses to the embryo fetus of less than
  15 to 20 rads are considered low risk..

40
Cardinal Principles of Radiation Protection

• Time Exposure is proportional to duration.
• Distance Governed by the inverse square law.
• Example If the dose is 5 R at 3 feet, stepping
  back to a distance of 6 feet will cause the dose
  to decrease to 1.25 R.
• Shielding A lead apron of at least 0.5-mm lead
  equivalence should be worn when exposed scatter
  (0.5 for a thyroid shield also).
• Radiographers should not be exposed to the
  primary beam. Non-radiation workers should be
  used to aid patients during exposure.
  
  

41
Radiographers Source of Exposure

• The Radiographers primary source of radiation
  exposure is Compton interactions that occur in
  the patient.
• Greatest exposure to technologists occur during
  fluoroscopy, portables, and surgery.
• Scattered beam intensity is about 1/1000 the
  intensity of the primary beam at a 90 degree
  angle at a distance of 1 meter from the patient.
• Collimation reduces the incidence of Compton
  interactions.

42
Protective Barriers

• Primary Barrier 1/16 inch lead equivalence
  located where primary beam strikes Extends from
  floor up to 7 feet high.
• Secondary Barrier 1/32 inch lead equivalence
  Extends from where primary barrier ends to
  ceiling with 1/2 inch overlap.
• X-ray control booth is a secondary barrier.
  Exposure switch must be short enough that the
  radiographer has to stand behind it.
• Lead window of booth is usually 1.5 mm lead
  equivalence.
• Uncontrolled Area General public areas (0.5
  rem) Controlled Rad personnel (5 rem)

43
Tube Housing

• X-rays may leak from the housing during exposure.
• Leakage may not exceed 100mR per hour at a
  distance of 1 meter from the housing.

44
Fluoroscopic Equipment

• Exposure Switch Dead man type.
• Protective Curtain 0.25-mm lead equivalent.
• Bucky Slot Shield 0.25-mm lead equivalent.
• Five-minute timer
• Portable units cord should be at least 6 ft long.

45
Monitoring

• Film Badges Plastic case, film, and filters
  measures doses as low as 10 mrem aluminum
  copper filters measure radiation intensity.
• Thermoluminescent Dosimeters (TLD) Lithium
  crystals record dose Crystals electrons become
  excited upon exposure and release this exposure
  on heating in the form of visible light.
  Exposures as low as 5 mrem.
• Pocket Ionization Chamber Small cylinder
  containing gas. Gas is ionized as it is struck by
  radiation After exposure, unit is held up to
  light and exposure scale can be viewed. Measures
  from 0-200 mR on its scale. Must be reset.
• Optically Stimulated Luminescence Dosimeter (OSL)
  Uses aluminum oxide to record dose It is then
  stimulated by a laser to release energy as
  visible light which indicates level of exposure.
  Exposures as low as 1 mrem. Can be worn up to 3
  months.

46
Area Monitoring

• Cutie Pie Meter Measures radiation in an area
  like a pocket ionization chamber using gas.
  Exposure rates as low as 1 mR per hour.
• Geiger-Mueller Detector Used to detect
  radioactive particles in nuclear medicine. Sounds
  audible alarm when struck by radiation.

47
The End