Introduction to Clinical Radiography

1
Introduction to Clinical Radiography

• RADI R103
• Unit II --Radiation Protection

2
Introduction to Clinical Radiography

• Unit IIRadiation ProtectionR103 Lecture 6

3
Background Information

• Basic assumptions about ionizing radiation (X
  rays other forms)
• -- potentially harmful to biologic tissue
• -- ionization of tissue atoms can change the
  normal structure function
• -- any level of exposure may cause damage
• -- body able to repair damage
• from low levels of exposure
• most of time

4
(No Transcript)
5
Background Information (cont.)

• Energy of x ray that enters object
• -- transmitted all x-ray energy exits
  unchanged
• -- absorbed all x ray energy deposited in
  tissue
• -- scattered part of the energy deposited
  possible for more interactions to occur
  (partial absorption)
• Deposited energy is what causes damage

6
SOURCES OF IONIZING RADIATION

• natural sources 82
• cosmic (from space)
• terrestrial (from earth)
• internal (in the body)
• radon (radioactive gas)
• manmade sources 18
• diagnostic x-ray procedures
• nuclear medicine procedures
• consumer products
• other

7
Concepts of Radiation Protection

• limiting ionizing radiation exposure
• Uses ALARA concept
• As Low As Reasonably Achievable
• views use of radiation in terms of RISK vs.
  BENEFIT
• Provides Standards and Guidelines (SG) for
  appropriate use of radiation

8
ALARA

• GOAL decrease exposure whenever possible
• does not eliminate radiation exposure
• provides guidelines to limit the risk of bodily
  injury

9
RISK vs. BENEFIT

• all exposure has "potential" for harm
• Benefit must outweigh Risk
• BENEFIT improvement in the persons life
• RISK a possible harmful effect
• (perceived or actual)
• requires use of good judgment

10
Common Risks
Accident Fatality risk/year
Motor vehicle 14,000
Fall 110,000
Fire 125,000
Lightening 11,000,000
Radiation 1300,000,000
11
Standards Guidelines (SG)

• set by the scientific community
• federal state legislation based on SG
• Organizations
• ICRP (International Commission on Radiological
  Protection)
• NCRP (National Council on Radiation Protection
  Measurements)
• NRC (Nuclear Regulatory Commission)
• Code of Federal Regulations (Title 10, part 20)

12
MEASURING RADIATION
Quantity Unit
Definition A physical property or characteristic that can be measured A standard used in measuring a quantity
Examples Distance meters, feet, etc.
Time seconds, hours, etc.
Speed mph
Radiation exposure roentgen, C/kg
13
EXPOSURE

• applies to x rays gamma rays only
• measures ionization of air
• electric charge ( of e- released by ionization)
• standard volume of air
• UNIT
• traditional ROENTGEN R
• SI coulomb/kilogram C/kg

14
ABSORBED DOSE

• measures amount of energy deposited in matter
• depends on energy of the radiation
• applies to any ionizing radiation
• measured in any matter
• UNIT
• traditional Radiation Absorbed Dose (rad)
• SI Gray (Gy)

15
DOSE EQUIVALENT

• measures relative biological effect
• only quantity used in radiation protection
• occupational exposure
• applies to any ionizing radiation
• absorbed dose times a quality factor
  (weighting) for the type of radiation
• UNIT
• traditional Radiation Equivalent Man (rem)
• SI sievert (Sv)

16
QUALITY FACTOR (QF)

• rem rad x QF
• QF (WR) varies for differing radiations

Radiation QF
X-rays gamma rays 1
Beta electrons 1
Thermal neutrons 5
Protons 20
Alpha particles 20
17
ACTIVITY

• applies to materials that emit radiation
• -- emit particles or EM energy from nucleus
• -- atoms are changing composition "decaying"
• activity of atoms decaying/unit time
• UNIT
• traditional CURIE (Ci)
• SI BECQUEREL (Bq)

18
Summary

19
Introduction to Clinical Radiography

• Unit IIRadiation ProtectionR103 Lecture 7

20
Overview - Harmful Effects

• 1. Sensitivity of living tissues

Sensitivity Cell type Examples
High Immature dividing embryonic, fetal, lymph
Intermediate cornea, liver
Low Mature not dividing muscle, brain, nerves
21

• 2. Somatic vs. Genetic Effects

Definition Examples
Somatic Harm to person exposed to the radiation Skin reddening (erythema), hair loss, nausea, etc.
Genetic Harm to person in future generation due to ancestors exposure ???(no unique effect), animal studies suggest links to increased mutations
22

• 3. Stochastic vs. Deterministic Effects

Traits Example
Stochastic all or none response statistical ? any dose can cause ? Incidence of a type of cancer in population
Deterministic (non stochastic) certainty effects severity of effect ? with ? dose minimum dose required Erythema all will experience once minimum dose is given gets worse with ? dose
23
EFFECTS ATTRIBUTED TO EXPOSURE

• 1. carcinogenesis
• no unique cancer
• most common cancer types
• leukemia
• thyroid cancer

24

• 2. somatic tissue damage
• cataract formation (long term exposures)
• erythemia (high exposure, short time period)
• life span shortening (long term exposures)

25

• 3. genetic effects
• no unique genetic defect
• evidence suggests an é in mutations with an é in
  radiation exposure

26

• 4. fetal (embryo) effects -- somatic
• effect depends on radiation dose stage of
  development of the fetus
• types of effects death, malformation, growth
  retardation, cancer
• most significant area of concern for Dx
  radiography

27
DOSE LIMITATIONS

• dose equivalent limits (maximum permissible dose)
  as established by NCRP
• doses with an acceptably small risk to the
  individual society
• does not include exposure from natural sources
  (background) of radiation
• radiation user responsible for limiting exposure
• provides upper limits of acceptable exposure
• actual exposure should be kept well below limit

28
NCRP Limits
Class of Individual Rems mSv
Occupational (annual)
stochastic effects 5 50
non stochastic
lens of eye 15 150
all other areas of body 50 500
lifetime cumulative (years) 1 x age 10 x age
Public (annual)
effective dose limit
frequent exposure 0.1 1
infrequent exposure 0.5 5
equivalent dose limits
lens of the eye 1.5 15
skin, extremities 5 50
Trainees under 18 years of age
effective dose limit 0.1 1
equivalent dose limits
lens of the eye 1.5 15
skin, extremities 5 50
Embryo-fetal exposures
total dose equivalent 0.5 5
dose equivalent limit in 1 month 0.05 0.5
29
Practical Radiation Protection

• Radiographers are responsible for radiation
  protection for
• ? themselves
• ? the patient
• ? fellow workers
• ? any others in the area

30
Protection -- Occupational Workers

• Three Principles that limit exposure
• TIME
• DISTANCE
• SHIELDING
• These principles also apply to all those in area
  who may be exposed to the radiation during an
  examination.

31

• 1. T I M E
• -- keep time spent in active area low
• -- do not be in room during exposure unless
  needed
• -- refers to radiographers working time
  not time set on the control console

32

• 2. D I S T A N C E
• -- increase the distance between you radiation
  source (scatter)
• -- radiation divergence means radiation will
  cover a larger area as distance increases
• -- learn use Inverse Square Law

33
Inverse Square Law

• inverse square of the distance change factor of
  change in radiation exposure
• find distance change

• invert square to find exposure change

34
Inverse Square Law

• example move from 4 to 6 ft from source

6 4

• result exposure at 6 is .44 X the exposure at
  4 (or 44 of the original exposure)

35

• 3. S H I E L D I N G
• use absorber between yourself radiation
• wear a lead apron if you will be in the exposure
  room
• wear lead gloves if your hands will be near the
  direct beam and patient
• use the control console wall/window as a barrier

36
EXPOSURE RECORDS

• Keep accurate occupational exposure records
• always wear your exposure badge
• report unusual exposures or misuse of badge
• change your badge at the appropriate time
• check the exposure report monthly
• learn how to interpret the report

37
Patient Protection

• significant responsibility of any x-ray machine
  operator
• acceptable radiographs can be produced with an
  unacceptable amount of exposure to the patient
• Pregnancy precautions

38
Beam Restriction

• use the collimation rule
• every image should be collimated
• reduces amount of patient receiving dose
• evidence of collimation

39
Pregnancy Precautions

• always ask female patients if there is a
  possibility for pregnancy
• check with physician before proceeding with an
  examination on a pregnant patient
• shield pelvic area of female patients on every
  exam unless it interferes with needed anatomy

40
Shield Patient

• use lead contact shields whenever possible
  (especially for gonads, thyroid, lens of eye)
• caution do not cover area needed on the image
  with a shield

41
Fast Imaging System

• é system speed will ê amount of radiation needed
  to produce an image
• caution too fast of a system will not provide
  detail needed for image

42
high kVp with a low mAs

• é kVp more penetrating beam of x rays
• require ê x rays to produce image (êmAs)
• fewer x rays lower dose
• é kVp only will not reduce patient exposure
• caution too high a kVp will not produce an
  appropriate film contrast

43
Avoid Errors

• errors require repeat exposures (i.e. more
  patient exposure)
• careful attention to detail (positioning of
  patient, selection of technical factors, etc.)

44
Beam Filtration

• Filter absorber inside tube/collimator assembly
  to absorb low energy radiation
• not usually a practical method