Protection from

Radiation

- basis principles

Department of Radiology Medical

University in Białystok

Exposure to radiation
involves risk. The
acceptance of risk,
however, is an unavoidable
part of any human activity.

Radiation sources

•

15% Human-made radiation sourses

- 78% Diagnostic X-rays

- 12% interventional radiology

- 7% nuclear medicine

- 1% radiation therapy

- 0,1% Laboratory and manufacturing

accidents.

•

85% Natural background radiation

What Radiation Affects

• Directly or indirectly, radiation

affects the DNA in cells

• DNA controls the cell’s function

and ability to reproduce

Possible Effects

• Destroy the DNA

– Kill the cell

• Damage the DNA; cell can:

– Repair itself (most likely)
– Not function or function improperly
– Undergo uncontrolled division

(cancer)

Cell Sensitivity

• Cells most affected:

– Rapidly dividing cells:
– (small intestines, bone marrow,

hair, fetus)

• Cells least affected:

– Slowly dividing cells:
– (brain, nerves)

Category of Effects

• Acute Somatic

– Immediate effects to the organism

receiving the dose

• Delayed Somatic

– Effects that appear years later to

organism receiving the dose

• Genetic

– Effects that appear in offspring

Units of Dose (SI)

• Dose measured as energy absorbed

per mass

– Units of Gray (Gy) or rad (= 0.01 Gy)

• Dose equivalent accounts for

different effect of different radiations

– Units of Sieverts (Sv) or rem (= 0.01 Sv)

• Dose measured equated to dose

equivalent

– 1 rad roughly equals 1 rem

Xeroderma pigmentosum is
characterized by sensitivity to
ultraviolet radiation.
Bloom syndrome and Fanconi
anemia both exhibit genomic
instability.
The syndrome that is associated
with the greatest sensivity to x rays
is ataxia telangiectasia .

The dose range that results

in an expected nausea

A total body dose in the range of
0.75–1.25Gy results in nausea in
5%–30% of persons exposed. At
higher doses in the range of 1.25–
3.00 Gy, the prevalence increases to
20%–70%. Above 5.3Gy, moderate to
severe nausea is expected in 50%–
90% of persons exposed.

The clinically detectable

effects of radiation of the

skin

• Transient erythema is evident in

hours, and the main wave of
erythema occurs after 10 days.
Epilation occurs after about 3weeks.
Ulceration and depigmentation are
late effects due to damage to the
dermis. Pain would be secondary to
extremely high doses.

Acute Somatic Effects

• <250 mSv (25 rem)

– No detectable effects

• 250 - 1,000 mSv (25 - 100 rem)

– Reduced red & white blood cell count

• 1,000 - 3,000 mSv (100 - 300 rem)

– Nausea, vomiting, may not be able to

fight infection

More Acute Somatic

• 3,000 - 6,000 mSv (300 - 600 rem)

– More severe nausea and vomiting,

hemorrhaging, diarrhea, loss of hair,

cannot fight infections, sterility. At 4,500

mSv, about half exposed will die within

30 days, others will survive.

• >6,000 mSv (600 rem)

– Same as above plus central nervous

system impairment. Death within 30

days.

Delayed Somatic Effects

• 1. Cancer: solid tumors

– Increased risk

• 2. Cancer: leukemia

– Increased risk

• 3. Degenerative effects

– Life shortening (not sure)

More Delayed Somatic

Effects

• 4. Cataracts

– 2,000 mSv single dose threshold

• 5. Birth defects (fetus exposed)

– Effects depend on time of gestation

• 6. Sterility

– 2,000 mSv temporary - male
– 8,000 mSv permanent - male

Cancer Risks

• Radiation dose above 10 rem

produces a

small increased risk

• Radiation dose does not produce

cancer in every exposed person

• Latency period:

– Solid tumors: 10 - 20 years
– Leukemia: 2 - 4 years

Most Common Cancers

• High spontaneous incidence:

– Breast, lung, skin, prostate, cervix, acute

myelogenous leukemia

• Moderate spontaneous incidence:

– Kidney & bladder, ovary, pancreas

• Low spontaneous incidence:

– Thyroid, liver, brain, testis, bone, chronic

lymphocytic leukemia

Radiation Induced

Cancers

• High sensitivity to radiation:

– Breast, thyroid, kidney & bladder,

ovary, acute myelogenous leukemia

• Moderate sensitivity to radiation:

– Lung, liver

• Low sensitivity to radiation:

– Brain, bone, skin, prostate, cervix

Radiation Induced Cancers

(continued)

• Not observed to be initiated by

radiation:

– Pancreas, testis, chronic lymphocytic

leukemia

Cancer Risks

• Increased risk of cancer mortality from 1

mSv of radiation (average annual
background):

– Solid tumor cancer risk is about one chance

out of 25,000 (1:25,000)

– Leukemia risk is about one chance out of

125,000 (1: 125,000)

– Total risk is about one chance out of 20,000

(1: 20,000)

Body regions

dose (mSv)

chest

radiographs

background

radiation

Radiography

Limbs and joints

0.01

0.5

1.5 days

Chest PA

0.02

3 days

Skull

0.1

2 weeks

Cervical spine

0.1

2 weeks

Thoracic spine

1.0

6 months

Lumbar spine

2.4

120

14 months

Hip

0.3

2 months

Pelvis

1.0

6 months

Abdomen

1.5

9 months

Barium swallow

2.0

100

1 year

Barium follow-through

5.0

250

2.5 years

Small-bowel

barium

enema

6.0

300

3 years

Large-bowel

barium

enema

9.0

450

4.5 years

Mammography

0.5

10 weeks

Computed tomography

Head

2.0

100

1 year

Chest; abdomen

8.0

400

4 years

Scintigraphy

Bone

5.0

250

2–5 years

Thyroid

1.0

6 months

Heart (thallium)

900

9 years

Deterministic effect

Deterministic are those for which the severity

of the effect varies with the dose, and no

effect occurs below a certain threshold.

The production of cataracts in the lens of the

eye is a deterministic effect with a threshold

value of 0.5 – 2.0 Sv . Doses below this

value do not induce cataracts. The

deterministic effects can be prevented by

setting dose limits low enough so that no

threshold dose would ever be reached

during a person's lifetime.

Stochastic effects

Stochastic effects are effects for which there
is no threshold and for which the severity of
the effects does not depend on dose,
although the probability that the effects will
occur does. Stochastic effects include
heritable effects and carcinogenesis, but not
cell killing. All biologic effects, stochastic or
otherwise, depend on all four factors: dose,
LET, dose rate, and type of tissue exposed.

Stochastic effects cannot be prevented
in this way because it is assumed that
there is no dose below which the effect
does not occur. Because the risk
associated with low level exposure to
radiation is believed to be proportional
to the absorbed dose it follows that the
risk is is reduced by minimizing the
exposure.

The International

Comission on

Radiological Protection

(ICRP)

recommends that the use of

radiation be governed by the

following three general principles:

The justification of

practice :

`No practice involving exposure
to radiation should be adopted
unless it produces sufficient
benefit to the exposed individual
or to society to offset the
radiation detriment it causes'.

The optimization of

protection :

`In relation to any particular source
within a practice, the magnitude of
individual doses, the number of
people exposed, and the likelyhood of
incurring exposures where these are
not certain to be received should all
be kept as low as reasonably
achievable, economic and social
factors being taken into account`.

The optimization of

protection :

`This procedure should be constrained by
restrictions on the doses (dose
constraints), or the risk to individuals in
the case of potential exposures (risk
constraints), so as to limit the inequity
likely to result from the inherent economic
and social judgements'. (this is popularly
referred to as the ALARA principle-

Low As Reasonably Achievable)

Individual dose and risk

limits :

`The exposure of individuals resulting from

the combination of all the relevant practices

should be subject to dose limits, or to some

control of risk in the case of potential

exposures. These are aimed at ensuring that

no individual is exposed to radiation risks

that are judged to be unacceptable from

these practices in any normal circumstances.

Not all sources are susceptible of control by

action at the source and it is necessary to

specify the sources to be included as

relevant before selecting a dose limit'.

Individual dose and risk

limits :

Occupational exposure consists of
the doses contributed by external
sources during working hours and
by internal sources taken into the
body during working hours. It does
not include any medical exposure
or exposure due to background
radiation .

Limits for Stochastic

Effects

In the case of uniform irradiation of the
whole body the ICRP   recommends a limit
on the effective equivalent dose of  50 mSv
in any one year and a limit  on the five-year
average of 20 mSv  per year. At the present
time the regulations of the Atomic Energy
Control Board   (AECB)  of Canada set a
limit  of 50 mSv  per year, but the
regulations are in the process of being
changed to reflect the most recent
recommendations of the ICRP.

Limits for Deterministic

Effects

The ICRP  believe that deterministic
effects  will be prevented if the limits for
stochastic effects  are observed. However
there is the need for an additional limit
for localised exposures of the skin and for
the lens of the eye. The recommended
annual limit  for localised exposure of the
skin is 500 mSv  averaged over any 1 cm2
per year. The annual equivalent-dose
limit  for the lens of the eye is 150 mSv  .

Additional Dose Limits for

Pregnant Workers

There is no special occupational dose
limit set by the ICRP for women in
general. However once pregnancy has
been declared the recommended
equivalent-dose limit  to the surface of
the women's abdomen (lower trunk) is 2
mSv  for the remainder of the pregnancy.
In addition the intake of radionuclides   is
restricted to less than  1/20 of the ALI.

Dose Limits for Members of

the General Public

The dose limits for members of the
general public are set by the ICRP by
comparing them to the exposure from
natural background  . The limits are set
at an effective dose of 1 mSv  per year.
For localised exposures to the skin the
limit is  50 mSv over any 1 cm2  area
and for the lens of the eye it is 15
mSv  .

Pregnant radiation worker

For a declared pregnancy, the dose limit to the

fetus is 500 mrem (5mSv). For fluoroscopy,

portable radiography, and nuclear medicine

imaging, the dose to the conceptus from

occupational exposure to the mother will very

likely be less than 5mSv if proper radiation

protection practices are followed. Radioiodine

treatments with I-131sodium iodide are

considered to place the fetus at higher probability

of exceeding 5mSv and are potentially very

hazardous in terms of uncontrolled release of the

radioactive material. The fetal thyroid takes up

radioiodine after age 12weeks.

NCRP recomendtions

concering occupational

exposure

The minimum age for occupationally exposed
workers is 18 years. It is assumed that medical
radiation confers some benefit, so it is not
included in the dose allowed to a person
occupationally exposed. ALARA is intended to
minimize occupational exposure. The purpose of
radiation protection for those occupationally
exposed is to prevent deterministic effects and
limit stochastic effects to levels that are
acceptable against a background of other risks
in society.

Protection of patient

• Equipment and apparatus design
Filtration
Collimation
Specific area shielding
Image receptors
• Radiographic technique
• Administrative procedures

Equipment and apparatus

design

Usually those features of
radiographic and fluoroscopic
equipment which are designed to
reduce patient dose will also reduce
exposure to the radiographer

Fitration

A minimum of 2.5 mm Al equivalent total
filtration is required on all fluoroscopic tubes
and for radiographic tubes operating above
70 kVp. The purpose of filtration is to reduce
the amount of low-energy radiation reaching
the patient. Because only higher energy x-
rays are useful in producing an image, low
energy x-rays are absorbed in the patient and
contribute only to patient dose, primarily to
the skin, and not to the radiographic or
fluoroscopic image. In general , the higher
the total filtration, the lower the patient dose.

Collimation

Collimation is the restriction of the

useful x-ray beam to the body part being

examined, thereby sparing adjacent

tissue from unnecessary exposure. The

larger the useful x-ray beam the higher

the patient dose. Restricting the x-ray

beam by collimation reduces not only

the volume of tissue irradiated but also

the absolute dose at any point because

of the

accompanying reduction in scatter

radiation.

Specific area shielding

In specific area shielding part of he
primary beam is absorbed during the
examination by shielding a specific area
of the body. There are two types:
shadow shields are attached to the
radiographic tube head and positioned
with the aid of the light localizer
between the tube and patient. Contact
shields are usually fabricated of vinyl
lead cut into various shapes and are
simply laid on the patient.

Specific area shielding

Gonad shielding should be used under
following conditions: 1) on all patients
of reproductive age, 2) when the
gonads lie in or near the useful beam,
and 3) when the use of such shielding
will not compromise the required
diagnostic information. Gonad
shielding will reduce the gonad dose
to near zero.

Image receptors

The speed of an image receptor can
greatly influence patient dose. The rare
earth screens developed in conjunction
with matched photographic emulsion
show relative speeds of up to twelve
times those of a conventional calcium
tungstate screen-film combination. rare
earth screen-film combinations will
reduce patient dose to one fourth can be
used with no loss of diagnostic
information.

Radiographic technique

Ideally, the higher the kVp the lower
the patient dose, because a large
reduction in mAs must accompany an
increase in kVp. However , as kVp is
raised, image contrast is reduced. In
general, the highest practicable kVp
with an appropriate low mAs should
be employed in all examinations.

Administrative procedures

• 10-day rule was first stated in 1970 by the

ICRP. If recommended that all x-ray
examinations of the abdomen or pelvis of a
fertile woman be performed only during
the 10 days following the onset of
menstruation

• The radiographer should never knowingly

conduct a radiologic examination on a
pregnant individual unless a documented
decision to do so has been made.

Document Outline

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