Pages 12, 13; 46, 47; 59-67; 77, 83-96;
appendices: 115-120,125
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Several factors impact the patient dose
◦ Body habitus
◦ Type of tissue exposed
 Tissue density – patient habitus and disease pathology
can alter tissue density
 Elemental composition (atomic number)
 The higher the A number of the tissue the more radiation is
absorbed
 Bone and aluminum have a similar A number (~13) lead is 82
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High kVp
Large field size (cone wide open)
Thick body part
Large field size is the largest factor
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Somatic dose is the dose that the person
themselves receives.
◦ This includes an embryo or fetus that is exposed in
the womb.
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Somatic changes that can occur are:
◦ Injuries to the superficial tissue
◦ Induction of cancer
◦ Cataract formation, impaired fertility, and life-span
shortening (the last one really doesn’t exist
anymore)
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Somatic Dose Indicators are used to measure
dose to specific areas of the body.
Measurement of one area can’t express the
entire somatic dose as:
◦ Primary beam is restricted so measuring a distant
point can’t tell you the dose of another area.
◦ Shielding may protect some areas during exposure
so measuring the protected area doesn’t give you
the dose of the unprotected area
◦ Some natural shielding occurs, some organs cover
other tissues.
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Somatic Dose Indicators are still useful,
however.
Bone Marrow
◦ Bone marrow dose is a reasonable indicator of
internal organs that are sensitive to cancer
induction (lung, GI tract).
 Irradiation of the bone marrow causes hematological
depression, particularly to the lymphocytes.
 A strong correlation exists between leukemia and the
mean radiation dose to the active bone marrow
 High bone marrow dose exams are: BE, UGI, and
abdominal angio
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Thyroid and Skin
◦ The somatic indicator of skin dose of the anterior
chest can be a reasonable indicator of breast dose
◦ The skin dose from an esophagram can be
indicative of the thyroid dose.
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Genetic Dose Indicators
◦ The genetic dose is indicated by the damage
exhibited by FUTURE offspring of the irradiated
person (NOT the embryo or fetus who was
themselves irradiated).
 When germ cells are irradiated changes may occur in
the genes/chromosomes of these cells and be passed
on to the descendants of the person who was
irradiated
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Genetically Significant Dose (GSD)
◦ The GSD is a statistic that helps us estimate the
magnitude of genetic effects caused by radiation
exposure in a population.
 The GSD is defined as the gonad dose which, if
received by every member of the population, would be
expected to produce the same total genetic effect on
the population as the sum of the individual doses that
are actually received. (does not include background
population
 3 parameters
 Number of future children
 X-ray exam rate
 Mean gonad dose per exam
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When something is irradiated and the energy
is transferred to matter ionizations and
excitations are produced
◦ Ionizations – electrons removed from an atom
◦ Excitations – electron vacancies in shells

Biological damage from ionizing radiation
seems to follow a linear, nonthreshold dose
relationship and it is influenced by:
◦ Dose rate to tissue
◦ Total dose received
◦ Type of cell irradiated
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Radiobiological Injury
◦ Cellular amplification – normal cellular metabolic
activity can amplify the radiation damage causing
the injury to move from the molecular to the
microscopic level and resulting in possible gross
cellular malfunction
◦ Gross cellular effects – the effect most often seen is
the cell stops dividing. It may be temporary or
permanent depending on the radiation damage.
 Factors seen: Chromosome breaks, clumping of
chromatin, abnormal mitoses, increased granularity of
cytoplasm, nuclear disintegration, changes in motility
or cytoplasmic activity, vacuolization, altered
protoplasmic viscosity, changes in membrane
permeability
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Radiobiological Injury
◦ Latent Period – where no injury shows up
 Early effects – seen in minutes, days, or weeks
 Late effects – years, decades, and generations later
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Determinants of Biological Effects
◦ 1. Dose-effect curve – a way to graph the dosage
administered against the probability of effect.
 Threshold –a point where there is no damage seen
 Non-threshold – always some effect
 Linear – as dose increases effect increases, directly
proportional
 Non-linear – takes into account fractionation and protraction
and other factors
 Radiation protection guidelines are based on linear nonthreshold
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Determinants of Biological Effects
◦ 2. area exposed and shielding – even partial
shielding of radiosensitive blood-forming organs
(spleen and bone marrow) can decrease the total
radiation effect (especially in children)
◦ 3. Variations in cell sensitivity – radiosensitivity
depends on the
 number of undifferentiated cells in the tissue
 degree of mitotic activity in tissue
 length of time cells stay in active prolifereation
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Determinants of Biological Effects
◦ 4. Short-term effects
 in general at 25 rads or less there are no indications of
injury (based on animal experimentation for the most part)
◦ 5. Long-term effects – manifest years later.
 Can be from acute or chronic low-level exposure.
 Long-term effects of low level dose on many people is more
of a health concern than high dose on a few people
 No unique disease associated with long-term effects they
are measured by statistic increase in some diseases
 Observed: somatic changes such as cancer, embryological
effects, cataracts. Genetic mutations that show up
generations later
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Determinants of Biological Effects
◦ 6. carcinogenic effects – human evidence that
radiation contributes to induction of cancer
 Early radiologists and dentists manifested an increase
in skin malignancies and leukemia
 Radium dial painters showed increase in bone
malignancies
 Uranium miners increase in lung cancer
 Japanese survivors of Hiroshima/Nagasaki increase in
leukemia and cancer
 Frequent radiation-induced cancers:
 Female breast, thyroid gland (women/children most),
hemopoietic tissue, lungs, GI tract, bones
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Determinants of Biological Effects
◦ 7. Embryological effects
 highly sensitive to radiation (immature,
undifferentiated, rapidly dividing cells)
 50 rad to fetus can result in spontaneous abortion
◦ 8. Cataractogenic effects
 Several hundred rads of acute dose
 Can tell if the cataract was caused by radiation
◦ 9. Life-span shortening
 Really doesn’t exist in today’s world
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Determinants of Biological Effects
◦ 10. Genetic Effects
 Gonads/germ cells can be damaged by radiation and
the damage is then passed on to future offspring and
can alter their genetic code
 Most genetic mutations are harmful, the more harmful
they are the quicker they will disappear.
 Animal experimentation tells us that:
 No indication of a threshold dose for genetic effects of
radiation
 Mutations appear to be dose-rate dependent. If the doserate is lower and protracted less damage is done
 Cones
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Daylight vision
Photopic vision
Perceive color
Concentrated in center
of retina
Visual acuity good
View “eye” on page 77
 Rods
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Nighttime vision
Scotopic vision
Perceive grays
Concentrated on the
periphery of the retina
Visual acuity poor
Be able to label eye
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Visual acuity
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Integration time
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Normal viewing distance
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The retina receives the images of external objects
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The blind spot
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The Macula Lutea is the exact center of the retina
◦ The ability to perceive fine detail
◦ The time required by the eye for recognition of an image is 0.2
second
◦ 12-15 inches
◦ Where the optic nerve enters the retina and there are no rods or cones
◦ There is a great increase in the number of cones and it is the region of
greatest visual acuity
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Doses given to children are much lower than
doses that adults receive, however, it can be
more dangerous as:
◦ their lifespan is longer so there is more time for
more radiation dose to occur and for damage to
manifest itself
◦ Children are more sensitive to radiation as their
tissues are young and rapidly dividing as they grow
(increased mitotic activity)
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The reason for repeats on children stems
from motion the majority of the time. You
can decrease motion by:
◦ Being friendly and nonthreatening
◦ Having the parents hold the child
◦ Secure children by mechanical means
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Protection for children
◦ Gonadal shielding is a must whenever the exam will
not be compromised.
◦ Avoid contrast-filled structures centering over
phototimer/Automatic Brightness Control as this
will increase patient dose
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Review appendix 5 for your own benefit and
understanding.
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The Pregnant Patient
◦ The interruption of pregnancy is never justified
because of radiation does to embryo/fetus from a
diagnostic x-ray exam, including abdominal exams
◦ Postpone exams of pregnant patients whenever
possible
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Occupationally Exposed Women
◦ A declared pregnant woman is one who has
voluntarily informed her employer, in writing, that
she is pregnant
◦ The dose equivalent to an embryo/fetus (during the
entire pregnancy) due to occupational exposure
should not exceed 0.5 rem (5 mSv)
◦ The radiation dose of the embryo/fetus shall not be
greater than 0.05 rem in any month (occupational
exposure)
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Isoexposure curves
◦ The main source of scattered radiation during
fluoroscopy is the patient
◦ Operator exposure to scattered radiation is directly
proportional to patient exposure and is influenced
by:
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kVp, area exposed, area exposed, thickness of body
part, time of exposure
◦ When the X-ray tube is located under the table
there is less exposure to the patient.
 Most of the exposure is under the table at angles of
135 and 120 degrees from the primary beam
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Review Appendices 13,14, 15 on pages
118, 119 and 120.
These appendices tell you:
◦ approximate organ doses by examination
◦ somatic detriment from common x-ray exams
◦ possibilities for dose reduction
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All hospitals shall maintain diagnostic
radiological services
All persons operating or supervising the
operation of X-ray machines shall comply with
the requirements of the Regulations Relating to
Radiologic Technology
Diagnostic radiological services may be
performed on the order of a person lawfully
authorized to give such an order
X-ray films or reproductions thereof, shall be
retained for the same period of time as is
required for other parts of the patient’s medical
record
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A physician shall have overall responsibility
for the radiological service.
Sufficient certified radiologic technologists
shall be employed to meet the needs of the
service being offered
There shall be at least one person on duty or
on call at all times capable of operating
radiological equipment
There shall be sufficient equipment and
supplies and space to adequately provide
radiological services.
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Review appendix 18 on p. 124 to see the
primary fluoroscopic beam attenuation
factors.
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Personnel Monitoring Devices
◦ Film Badge
 Detects x-rays, gamma, beta, thermal neutrons, fast
neutrons
 Range: 0.0-700 rad
 Detects 10keV for gamma and 200 keV for beta
 Advantages: inexpensive, estimates of integrated dose,
permanent records, objective review, detects problems
 Disadvantages: moderate directional dependence,
strong energy dependence for low energy x-rays, false
readings produced by heat, pressure, vapors
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Personnel Monitoring Devices
◦ Thermoluminescent Dosimeter (TLD)
 Detects x-rays, gamma, beta, thermal, neutrons, fast
neutrons
 Range: 10 mrads to 10 5 rad
 Detects 10 keV minimum
 Advantages: infinite shelf life, small size, low
directional dependence, reusable, inexpensive,
integrated dose estimates
 Disadvantages: cancellation of dose upon reading,
dose range depends on sensitivity of reader, increased
sensitivity with each use, subjective info
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Personnel Monitoring Devices
◦ Pocket Ionization Chamber
 Detects: x-rays, gamma, beta, thermal neutrons, fast
neutrons
 Range: 0.001 to 2000 rads (theoretical), x-rays 0.001-200
millirads
 Detects: 10 keV for gamma, 20keV for fast neutrons
minimum
 Advantages: accurate info quickly, small size, low directional
dependence, economical, little maintenance, reusable
 Disadvantages: no permanent record, frequent reading
tabulation, recharging may be required, subject to accidental
discharge (shock, electrical leakage, range of measurement
is limited
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Protective aprons do not eliminate all
exposure
◦ 0.25 mm lead equivalent eliminates 96% while 0.5
mm eliminates 99%
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Remnant radiation, that emerges from the
patient, and forms them image, is only 5% of the
incident photons
The minimum source-to-skin distance for
portable fluoroscopic equipment is 12” and
should be at least 18” for stationary fluoroscopic
equipment
P. 60 50 rads, in one dose, can result in cessation
of sperm formation, however, fertility is not
impaired until preexisting sperm are eliminated
which takes weeks. It is a temporary impairment
not permanent sterility
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Females have all of their germ cells, or
ooctyes and can not replace them as the male
replaces sperm.
◦ Ooctyes are radiosensitive as irradiation causes a
lasting reduction in reproductive potential. 30 rads
in one dose can cause temporary sterility.
◦ These doses, to the gonads, should not be
encountered in the diagnostic radiology arena.