STUDY GUIDE – RT 244 (Notes from Bushong’s text)
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Radiation Protection & Radiobiology Notes
Human Biology
 Human Response To Ionizing Radiation
 Early Effects of Radiation: When response occurs within minutes or days after
exposure.
 Late Effects of Radiation: When response is not observed for many months or
years after exposure.
 Effects of fetal irradiation: Death, malformation, malignancy, diminished growth.
 Composition of Human Body
 Cell Theory: 85% of the body is hydrogen and oxygen.
 Hydrogen: 60%
 Carbon: 10.7%
 Oxygen: 25.7%
 Nitrogen: 2.4%
 Molecular Composition
 Water: 80% - A simple molecule.
 Protein: 15% - A macromolecule.
 Fat: 2% - A macromolecule.
 Other: 3%
 Tissues and Organs: (The most radiosensitive cells in the human body are
Lymphocytes & Spermatogonia.
Fundamental Principles of Radiobiology
 Law of Bergonie and Tribondeau
 1) Older cells are more radioresistant.
 2) Younger cells are more radiosensitive.
 How these principles apply to radiation safety: The fetus is more radiosensitive
to radiation than a child or adult.
 Biologic Factors Affecting Radiosensitivity
 Age: Humans are most sensitive before birth.
 Gender: Females are less radiosensitive than males.
Molecular and Cellular Radiobiology
 Irradiation of Macromolecules: (p.450) Follows a Linear, Non-threshold
dose/response relationship.
 Radiation Effects on DNA: DNA is the most radiosensitive macromolecule.
 1) Cell death
 2) Malignant disease
 3) Genetic damage
 Radiolysis of Water: Indirect Effect. Most prevalent in humans.
 We are mostly water: 80% Water
 The breakdown of water by radiation is harmful.
 Breakdown products, called free radicals, cause DNA damage.
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 DNA damage can cause somatic and genetic outcomes.
Direct and Indirect Effect
 Direct Effect: Radiation hits DNA causing cell damage.
 Indirect Effect: 2 Step process The principle action of radiation on humans is the
Indirect Effect.
 1) Radiation breaks down water molecules.
 2) Break down products (free radicals) damage DNA.
Single-Target, Single-Hit Model
 Poisson Distribution: A statistical law. If 100 rain drops fell on 100 squares, 63%
will be wet, 37% will be dry.
Early Effects of Radiation
 Acute Radiation Lethality: X-ray beams are not large or intense enough to
cause radiation lethality.
 Early Effects: See a radiation response within a few days.
 Local Tissue Damage:Requires a higher dose to produce a response. Results
in tissue atrophy.
 Skin: Erythema- a sunburn-like redness. SED50 (Skin Erythema Dose to affect
50% of pop.) at 600 Rad.
 Gonads: Ovaries & Testes are very sensitive to radiation. Permanent sterility at
500 Rad.
Late Effects of Radiation
 Local Tissue Effects
 Skin: High doses of radiation causes discolored and weathered appearance of
skin.
 Chromosomes: Damage to lymphocytes can produce both an early and a late
response.
 Cataracts: The eye's sensitivity is age dependent. Increase in age, increases
effects. Cataracts at 1,000 Rad
Life Span Shortening
 10 days per rad: You can loose 10 days of life for every rad received.
 Relative safety of occupation: Radiologic Technology is considered a safe
occupation.
Risk Estimates
 Relative Risk: Observed cases ÷ Expected cases. Estimate used when you
don't know the original dose.
 Excess Risk: Observed cases - Expected cases. Estimate using the excess
cases induced.
 Absolute Risk: Estimate using 2 known dose levels.
Radiation Induced Malignancy
 Leukemia: Linear, Non-threshold. 4-7 year latent period. 20 year "at risk" period.
 Thyroid Cancer: Linear, Non-threshold dose/response relationship.
 Bone Cancer: Radium watch-dial painters developed bone cancer.
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 Skin Cancer: Follows a threshold dose/response relationship.
 Breast Cancer: Atomic blast survivors who received 10 Rads plus, exhibited a
risk factor of 4:1.
 Lung Cancer: Uranium miners show a risk factor of 8:1.
 Liver Cancer: "Thorotrast" contrast agent, caused liver cancer after 15-20 year
latent period.
 Total Risk of Malignancy
 Overall Absolute Risk of Malignancy: (p.487) Approximately 10 cases/106
persons/rad/year, 25 years after exposure.
 Radiation and Pregnancy
 Irradiation in Utero: High dose may interrupt fertility.
 First two weeks: The first two weeks of pregnancy may be the safest. A high
dose may produce a spontaneous abortion. This is an all or none
dose/response relationship.
 Major organ formation: From the 2nd - 10th week of gestation. High rad dose
will produce skeletal, organ and CNS abnormalities.
 Summary of effects
 Health Physics
 Cardinal Principles of Radiation Protection: Time, Distance and Shielding.
 Minimize Time: Keep exposure time as short as possible.
 Exposure = exposure rate x time
 Maximize Distance: Use the longest SID possible from the source.
 Doubling the distance drops the exposure by 4 times.
 Technologist should be as far from the source as practical.
 Maximize Shielding: Insert shielding between the source and person.
 Half Value Layer of Lead (at 80kVp): .19mm Lead.
 Tenth Value Layer of Lead (at 80 kVp): .64mm Lead.
 Dose Limit (DL)
 Definition: Ensures that radiation workers have the same risk as those in safe
industries. There is no patient DL.
 Summary of DL:
 Summary of NCRP Dose Limit Recommendations. (See the last page of this
guide.)
 Annual DL is still 5 rem/yr (50 mSv/yr)
 Cumulative DL is 1 Rem x age (10 mSv x age)
 Educational Considerations
 ALARA principle: Maintain radiation exposures As Low As Reasonably
Achievable.
X-Rays and Pregnancy
 Radiobiology of Pregnancy: Time dependence (first 2 weeks are safest) &
dose dependence (200 Rad dose will certainly cause radiation effects).
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 The Pregnant Radiographer: DL = 5 mSv/9 months. Should wear 2 film badges,
one at collar, one at waist.
 Pregnancy in Diagnostic Radiology
 Fetal Dose by Exam: An AP L-Spine exam of the mother gives the highest fetal
dose.
Designing for Radiation Protection
 Design of X-ray Apparatus
 Requirements of the Control Panel: Must show two things.
 1) Display conditions of exposure.
 2) Positively indicate when x-rays are being produced.
 Radiation Protection Designs For X-ray Equipment
 Source-to-Image Distance Indicator: A tape measure. Must be accurate to
within 2% of SID.
 Collimation: Light localized, variable aperture. Must be within 2% of SID.
 1) Light Localizer: Light bulb.
 2) Variable Aperture Collimation: Can be adjusted by the Technologist.
 3) X-ray field/ light field agreement. Must be within 2% of the SID.
 Positive Beam Limitation (PBL): Automatic Collimators. Must be accurate to
within 2% of the SID.
 Beam Alignment Device (cross-hair target): Line up the cross-hair target for
proper tube/film alignment.
 Filtration: 2.5mm Aluminum at 70 kVp.
 Design of Protective Barriers
 Types of Radiation:
 Primary Radiation: The useful beam.
 1) Most of the radiation comes from primary beam.
 2) Most dangerous.
 3) Hardest to shield against.
 Primary Barriers: Any wall to which the useful beam can be directed.
 Secondary Radiation: 2 types
 1) Scatter Radiation: Comes from the patient.
 2) Leakage Radiation Comes from the tube.
 Secondary Barriers: The control booth barrier is a secondary barrier. Do not
have to contain lead.
 Radiation Detection and Measurement
 Types of Dosimeters: 1) Film Badges: Used most often. Have a limited range.
Not reusable.
 2) Thermoluminescent Dosimeter (TLD): Have a wide range. Are reusable.
Radiation Protection Procedures
 Estimation of Patient Dose
 Skin Dose: Easiest to measure using TLD's.
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 Gonadal Dose: Important because of suspected genetic response. GSDGenetically Significant Dose.
 Bone Marrow Dose: Important because bone marrow is the target organ
believed responsible for leukemia.
 Reduction of Occupational Exposure: Do not aim the tube toward the control
booth barrier.
 Personnel Monitoring: Required when you will receive more than 1/4th the DL.
 Film Badges: Cheap, easy to use, easy to process, accurate and have been
used for decades.
 TLD: Newer, can be worn for up to 3 months.
 Pocket Ionization Chamber: Must be charged daily before use.
 Patient Holding: Radiology personnel should never be used to hold patients.
Use family or friends of patient.
 Reduction of Unnecessary Patient Dose
 Unnecessary Examinations: The technologist has no control over this.
 Repeat Examinations: The # 1 reason for high patient dose. Due to patient
positioning over the photo-cells.
 Radiographic Technique: Use high kVp technique to reduce patient dose.
 The Image Receptor: Use the fastest film/screen combination to reduce patient
dose.
 Patient Positioning: Be sure the useful beam does not intercept the gonads if
patient is seated for extremity films.
 Specific Area Shielding: The lens of the eye, breasts and gonads are frequently
shielded from the primary beam.
From NCRP Report No. 116 Limitation of Exposure to Ionizing Radiation Issued:
Summary of Recommendations
A. Occupational exposures
 1. Effective dose limits
 a) Annual 50 mSv/yr (5 Rem/yr)
 b) Cumulative 10 mSv x Age (1 Rem x Age)
 2. Equivalent dose annual limits for tissues and organs
 a) Lens of eye 150 mSv (15 Rem)
 b) Skin, hands and feet 500 mSv (50 Rem)
 B. Guidance for emergency occupational exposure (not listed)
 C. Public exposures (annual) are 1/10th the occupational exposures.
 1. Effective dose limit, continuous or frequent exposure 1 mSv (0.1 Rem)
 2. Effective dose limit, infrequent exposure 5 mSv (.5 Rem)
 3. Equivalent dose limits for tissues and organs
 a) Lens of eye 15 mSv (1.5 Rem)
 b) Skin, hands and feet 50 mSv (5 Rem)
 4. Remedial action for natural sources:
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a) Effective dose (excluding radon) >5 mSv
b) Exposure to radon decay products >7 x 10-3 Jh m-3
D. Education and training exposures (annual)
1. Effective dose limit 1mSv (0.1 Rem)
2. Equivalent dose limit for tissues and organs
a) Lens of eye 15 mSv (1.5 Rem)
b) Skin, hands and feet 50 mSv (5 Rem)
E. Embryo-fetus exposures (monthly)
1. Equivalent dose limit 0.5 mSv (.05 Rem)
F. Negligible individual dose (annual) 0.01 mSv (.001 Rem)
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