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Acute Radiation
Syndrome (ARS) (sometimes known as radiation toxicity or radiation sickness)
is an acute illness caused by irradiation of the entire body (or most
of the body) by a high dose of penetrating radiation in a very short period
of time (usually a matter of minutes). The major cause of this syndrome
is depletion of immature parenchymal stem cells in specific tissues. Examples
of persons who suffered from ARS are the survivors of the Hiroshima and
Nagasaki atomic bombs, the firefighters that first responded after the
Chernobyl Nuclear Power Plant event in 1986, and some unintentional exposures
to sterilization irradiators.
The
required conditions for Acute Radiation Syndrome (ARS) are:
- The
radiation dose must be large
(i.e., greater than 0.7 Gray (Gy)1, 2
or 70 rads).
- Mild
symptoms may be observed as low as 0.3 Gy or 30 rads.
- The
dose usually must be external (i.e., the source of radiation
is outside of the patient ’s body).
- Radioactive
materials deposited inside the body have produced some ARS effects
only in extremely rare cases.
- The
radiation must be penetrating (i.e., able to reach the internal
organs).
-
High energy X-rays, gamma rays, and neutrons are penetrating radiations.
- The
entire body (or a significant portion of it) must have received
the dose3.
- Most
radiation injuries are local, frequently involving the hands, and
these local injuries seldom cause classical signs of ARS.
- The
dose must have been delivered in a short time (usually a matter
of minutes).
-
Fractionated doses are often used in radiation therapy. These are
large total doses delivered in small daily amounts over a period
of time. Fractionated doses are less effective at inducing ARS than
a single dose of the same magnitude.
The
three classic ARS Syndromes are:
- Bone
marrow syndrome (sometimes referred to as hematopoietic syndrome)
the full syndrome will usually occur with a dose between 0.7 and 10
Gy (70 – 1000 rads) though mild symptoms may occur as low as 0.3
Gy or 30 rads4.
- The
survival rate of patients with this syndrome decreases with increasing
dose. The primary cause of death is the destruction of the bone
marrow, resulting in infection and hemorrhage.
- Gastrointestinal
(GI) syndrome: the full syndrome will usually occur with a
dose between 10 and 100 Gy (1000 – 10,000 rads) though some symptoms
may occur as low as 6 Gy or 600 rads.
- Survival
is extremely unlikely with this syndrome. Destructive and irreparable
changes in the GI tract and bone marrow usually cause infection,
dehydration, and electrolyte imbalance. Death usually occurs within
2 weeks.
- Cardiovascular
(CV)/ Central Nervous System (CNS) syndrome: the full syndrome
will usually occur with a dose greater than 50 Gy (5000 rads) though
some symptoms may occur as low as 20 Gy or 2000 rads.
- Death
occurs within 3 days. Death is likely due to collapse of the circulatory
system as well as increased pressure in the confining cranial vault
as the result of increased fluid content caused by edema, vasculitis,
and meningitis.
The four stages
of ARS are:
- Prodromal
stage (N-V-D stage): The classic symptoms for this stage are
nausea, vomiting, and possibly diarrhea (depending on dose) that occur
from minutes to days following exposure. The symptoms may last (episodically)
for minutes up to several days.
- Latent
stage: In this stage the patient looks and feels generally
healthy for a few hours or even up to a few weeks.
- Manifest
illness stage: In this stage the symptoms depend on the
specific syndrome (see Table 1) and last from
hours up to several months.
- Recovery
or death: Most patients who do not recover will die within
several months of exposure. The recovery process lasts from several
weeks up to two years.
These Stages
are described in further detail in Table 1, below.
Table
1: Acute Radiation Syndromes
Syndrome |
|
Prodromal
Stage |
Latent
Stage |
Manifest
Illness Stage |
Recovery |
Bone
Marrow (Hematopoietic) |
0.7
– 10 Gy (70 –1000 rads)
(mild symptoms may occur as low as 0.3 Gy or
30 rads) |
|
anorexia,
nausea and vomiting |
|
occurs 1 hour to 2 days after exposure |
|
lasts for minutes to days |
|
|
stem
cells in bone marrow are dying, though patient may
appear and feel well |
|
lasts
1 to 6 weeks |
|
|
drop
in all blood cell counts for several weeks |
|
anorexia,
fever, malaise |
|
primary
cause of death is infection and hemorrhage |
|
survival
decreases with increasing dose |
|
most
deaths occur within a few months after exposure |
|
|
in
most cases, bone marrow cells will begin to repopulate
the marrow |
|
there
should be full recovery for a large percentage of
individuals from a few weeks up to two years after
exposure |
|
death
may occur in some individuals at 1.2 Gy (120 rads)
|
|
the
LD50/606 is about 2.5
to 5 Gy (250 to 500 rads) |
|
Gastrointestinal
(GI) |
10
– 100 Gy (1000 – 10,000 rads)
(some symptoms may occur as low as 6 Gy or
600 rads) |
|
anorexia,
severe nausea, vomiting, cramps and diarrhea |
|
occurs
within a few hours after exposure |
|
lasts
about 2 days |
|
|
stem
cells in bone marrow and cells lining GI tract are
dying, though patient may appear and feel well |
|
lasts
less than 1 week |
|
|
malaise,
anorexia, severe diarrhea, fever, dehydration, electrolyte
imbalance |
|
death
is due to infection, dehydration and electrolyte imbalance
|
|
death
occurs within 2 weeks of exposure |
|
|
the
LD1007 is about 10 Gy
(1000 rads) |
|
Cardiovascular
(CV)/ Central Nervous System (CNS) |
>
50 Gy (5000 rads)
(some symptoms may occur as low as 20 Gy or
2000 rads) |
|
extreme
nervousness; confusion; severe nausea, vomiting, and
watery diarrhea; loss of consciousness; burning sensations
of the skin |
|
occurs
within minutes of exposure |
|
lasts
for minutes to hours |
|
|
patient
may return to partial functionality |
|
may
last for hours but often is less |
|
|
return
of watery diarrhea, convulsions, coma |
|
begins
5 to 6 hours after exposure |
|
death
within 3 days of exposure |
|
|
|
|
Cutaneous
Radiation Syndrome (CRS)
The concept
of cutaneous radiation syndrome (CRS) was introduced in recent years to
describe the complex pathological syndrome resulting from acute radiation
exposure to the skin.
ARS will
usually be accompanied by some skin damage. It is also possible to receive
a damaging dose to the skin without symptoms of ARS, especially with acute
exposures to beta radiation or x-rays. Sometimes this occurs when radioactive
materials contaminate a patient’s skin or clothes.
When the
basal cell layer of the skin is damaged by radiation, inflammation, erythema,
and dry or moist desquamation can occur. Also, hair follicles may be damaged
causing epilation. Within a few hours after irradiation a transient and
inconsistent erythema (associated with itching) can occur. Then, there
may be a latent phase that lasts from a few days up to several weeks,
when intense reddening, blistering and ulceration of the irradiated site
is visible.
In most
cases healing occurs by regenerative means; however, very large skin doses
can cause permanent hair loss, damaged sebaceous and sweat glands, atrophy,
fibrosis, decreased or increased skin pigmentation, and ulceration or
necrosis of the exposed tissue.
Patient Management
- Triage:
If radiation exposure is suspected:
- Secure
ABCs (airway, breathing, circulation) and physiologic monitoring
(blood pressure, blood gases, electrolyte and urine output) as appropriate.
- Treat
major trauma, burns and respiratory injury if evident.
- In
addition to the blood samples required to address the trauma, obtain
blood samples for CBC (complete blood count), with attention to
lymphocyte count, and HLA (human leukocyte antigen) typing prior
to any initial transfusion and at periodic intervals following transfusion.
- Treat
contamination as needed.
- If
exposure occurred within 8 to 12 hours, repeat CBC, with attention
to lymphocyte count, 2 or 3 more times (approximately every 2 to
3 hours) to assess lymphocyte depletion.
- Diagnosis
The diagnosis of ARS can be difficult to make because it causes no unique
disease. Also; depending on dose, the prodromal stage may not occur
for hours or days after exposure, or, the patient may already be in
the latent stage by the time they receive treatment, in which case the
patient may appear and feel well when first assessed.
If a patient received more than 0.05 Gy (5 rads) and 3 or 4 CBCs
are taken within 8 to 12 hours of the exposure, a quick estimate
of the dose can be made (see Ricks, et. al.
for details). If these initial blood counts are not taken, the dose
can still be estimated using CBC results over the first few days.
It would be best to have radiation dosimetrists conduct the dose
assessment, if possible.
If a patient is known or suspected of having been exposed to a large
radiation dose, draw blood for CBC analysis, with special attention
to the lymphocyte count, every 2 to 3 hours for the first 8 hours following
exposure (and every 4 to 6 hours for the following 2 days). Observe
the patient during this time for symptoms and consult with radiation
experts before ruling out ARS.
If no radiation exposure is initially suspected you may consider ARS
in the differential diagnosis if there is a history of nausea and vomiting
that is unexplained by other causes. Other indications are bleeding
or epilation or WBC (white blood count) and platelet counts abnormally
low a few days or weeks following unexplained nausea and vomiting. Again,
consider CBC and chromosome analysis and consultation with radiation
experts to confirm diagnosis.
- Initial
Treatment and Diagnostic Evaluation
Treat vomiting8, and repeat CBC analysis,
with special attention to the lymphocyte count, every 2 to 3 hours for
the first 8 to 12 hours following exposure (and every 4 to 6 hours for
the following 2 or 3 days). Precisely record all clinical symptoms,
particularly nausea, vomiting, diarrhea, and itching, reddening or blistering
of the skin. (Be sure to include time of onset.)
Note and record areas of erythema. If possible, take color photographs
of suspected radiation skin damage. Consider tissue, blood typing, and
initiating viral prophylaxis. Promptly consult with radiation, hematology,
and radiotherapy experts in regards to dosimetry, prognosis and treatment
options. Call the Radiation Emergency Assistance Center/Training Site
(REAC/TS) at (865) 576-3131 (M-F, 8 am to 4:30 am EST) or (865) 576-1005
(after hours) to record the incident in the Radiation Accident Registry
System.
After consultation, begin the following (as indicated):
- supportive care in a clean environment (if available, the use
of a burn unit may be quite effective)
- prevention and treatment of infections
- stimulation of hematopoiesis by use of growth factors
- stem cell transfusions or platelet transfusions (if platelet count
is too low)
- psychological support
- careful observation for erythema (document locations), hair loss,
skin injury, mucositis, parotitis, weight loss, or fever
- confirmation of initial dose estimate using chromosome aberration
cytogenetic bioassay when possible. Though resource intensive, this
is the “gold standard” for dose assessment following
acute exposures.
- consultation with experts in radiation accident management
For More Help
Technical
assistance can be obtained from the Radiation Emergency Assistance Center/Training
Site (REAC/TS) at (865) 576-3131 (M-F, 8 am to 4:30 pm EST) or (865) 576-1005
(after hours), or on their internet site at http://www.orau.gov/reacts/,
and the Medical Radiobiology Advisory Team (MRAT) at (301) 295-0316.
Also, more
information can be obtained from the CDC Health Alert Network at http://www.bt.cdc.gov
or by calling 1-800-311-3435.
References
Gusev, I.
A., et. al., Eds., 2001, Medical Management of Radiation Accidents, Second
Edition, CRC Press, Inc., New York, New York.
Jarrett,
D. G., 1999, Medical Management of Radiological Casualties Handbook, First
Edition, AFRRI (Armed Forces Radiobiology Research Institute), Bethesda,
Maryland.
LaTorre
Travis, E., 1989, Primer of Medical Radiobiology, Second Edition, Year
Book Medical Publishers, Inc., Chicago, Illinois.
NCRP (National
Council on Radiation Protection and Measurements), October 24, 2001, Management
of Terrorist Events Involving Radioactive Material, NCRP Report No. 138,
National Council on Radiation Protection and Measurements, Bethesda, Maryland.
Prasad,
K. N., 1995, Handbook of Radiobiology, Second Edition, CRC Press, Inc.,
New York, New York.
Ricks,
R.C., et. al., Eds. ,2002, The Medical Basis for Radiation Accident Preparedness:
The Clinical Care of Victims, Parthenon Publishing, New York.
- The Gray (Gy) is a unit of absorbed dose and reflects
an amount of energy deposited into a mass of tissue (1 Gy = 100
rads). In this document, the absorbed dose we are referring to is
that dose inside the patient's body (i.e., the dose which is normally
measured with personal dosimeters).
- The referenced absorbed dose levels in this document
are assumed to be from beta, gamma or x radiation. Neutron or proton
radiation produces many of the health effects described herein at
lower absorbed dose levels.
- The dose may not be uniform, but a large portion
of the body must have received more than 0.7 Gy (70 rads).
- Note that though the dose ranges provided in this
document apply to most healthy adult members of the public, there
is a great deal of variability of radiosensitivity among individuals,
depending in large part on the age and condition of health of the
individual at the time of exposure. Children and infants are especially
sensitive.
- The absorbed doses quoted here are gamma equivalent
values. Neutrons or protons generally produce the same effects as
gamma, beta or X-rays, but at lower doses. If the patient has been
exposed to neutrons or protons, consult radiation experts on how
to interpret the dose.
- The LD50/60 is the dose necessary to kill 50%
of the exposed population in 60 days.
- The LD100 is the dose necessary to kill 100% of
the exposed population.
- Collect vomitus in the first few days for later
analysis.
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