Pediatric emergency medicine trisk 494

FIGURE 90.10 Types of radiation.

Alpha particles have a 2+ electrical charge and a large mass (two protons and
two neutrons). Beta particles have a single negative charge and a small mass (one
electron). Charged particles do not penetrate the body very well. Because of their
larger mass and charge, alpha rays cannot penetrate even the dead layers of skin.
239Pu (plutonium), an alpha emitter, is a biologic hazard only when it is inhaled,
ingested, or otherwise introduced into the body. Beta particles (“beta rays”) are
more penetrating and in high doses can severely damage the skin. Beta rays
cannot damage the deep radiation-sensitive organs in the body unless the
radioactive source is incorporated into the body. At the Chernobyl nuclear plant
accident in Ukraine, some of the firefighters had severe skin damage due to
intense beta particle exposure, which contributed to their deaths.
The words “radiation” and “radioactive” are often confused. An atom that is
unstable spontaneously gives off energy as radiation and is therefore radioactive.
In contrast, an x-ray machine cannot spontaneously give off radiation: an external
power source is needed. Therefore, an x-ray machine is not radioactive. A patient


who has been exposed to radiation does not become radioactive. Patients emit
radiation only if they have radioactive atoms on them (external contamination) or
within them (internal contamination).
Amounts of Radiation
Geiger counters can measure amounts of radiation far below levels that have a
measurable biologic effect. They are inexpensive and readily available in the
nuclear medicine department at most hospitals. Because a Geiger counter can
detect and quantify the radiation exposure rate immediately, detecting and
managing a radiation hazard may be easier than detecting and managing biologic
or chemical hazards.
Radiation exposure is commonly measured in three different units in the
United States: roentgen, rad, and rem. However, new international units are being

used by regulatory and professional organizations ( Table 90.10 ). The roentgen
(R) is a measure of radiation exposure in air. Absorbed dose in an organ is
measured in grays (Gy); 1 Gy is equal to 100 rads. Effective dose, in sieverts
(Sv), is a measure of overall risk to an individual when the irradiation is weighted
for the sensitivity of each organ to late effects of radiation. One sievert is equal to
100 rems. Quantity of radioactivity is measured by becquerels (Bq), defined as 1
atomic disintegration per second. The former unit, the curie (Ci), is equal to 3.7 ×
1010 Bq, and 1 mCi is equal to 37 MBq.


TABLE 90.10
INTERNATIONAL RADIATION UNITS
Metric

Definition

Exposure

Roentgen, R
R = 2.58 × 10− 4 C/kg air

Absorbed dose

Gray, Gy
1 Gy = 1 J/kg

Effective dose

1 Gy = 100 rads
Sievert, Sv

1 Sv = 1 J/kg, weighted for tissue
sensitivity

Quantity of radioactivity

1 Sv = 100 rems
Becquerel, Bq
Curie, Ci
1 Bq = 1 disintegration/s
1 Ci = 3.7 × 1010 Bq
1 mCi = 37 MBq

Note: C = coulomb.

TABLE 90.11
COMMON RADIATION DOSES
Sources

Effective dose

Roundtrip intercontinental air flight

20–30 μSv

Chest radiograph
Living in brick house

50–100 μSv
0.20 μSv/yr

Natural radiation
Angiography

3 mSv/yr
10 mSv

Abdominal computed tomographic scan

10–30 mSv

We are exposed to about 3 mSv of radiation each year from natural sources.
During a 70-year lifetime, a person’s total radiation exposure from natural sources


will be more than 200 mSv, with no known measurable biologic effect. Typical
radiation exposures encountered during life and in medicine are listed in Table
90.11 . Children generally have a higher relative risk of cancers (leukemia and
thyroid, skin, breast, and brain cancer) following radiation exposure compared to
adults, likely due to the increased radiosensitivity of their developing organs.
Also, since children are shorter than adults, they may be exposed to radioactive
material deposited on the ground. In addition, their shorter body diameters can
lead to higher-dose exposures to their internal organs.
The hazard posed by a radionuclide depends on its quantity, decay scheme, the
energies of its emissions, its half-life, and length of exposure. For example, a
radionuclide that decays by emitting only alpha particles is not a hazard if kept
outside the body, since alpha particles cannot penetrate even the dead layers of
the skin. However, some radionuclides (e.g., 131Iodine) that are readily absorbed
by the body and/or are concentrated by an organ can be a hazard in small
amounts.
Although the radiation doses to personnel involved in the care of a victim

contaminated by radioactive material are likely to be very small, simple
protective measures should be employed to minimize the doses. There are three
methods of protection from radiation exposure: minimizing time of exposure,
maximizing distance from the material to the extent practical, and using shielding
as appropriate. The amount of exposure received is directly proportional to the
time spent near the source of radiation. Distance is the most practical and
effective method of reducing radiation exposure because the dose decreases by
the square of the distance ( Fig. 90.11 ). This is known as the inverse square law.
The lead aprons used in radiology departments, where the radiation comes from
low-energy, scattered, nonparticulate radiation, are not generally useful in
radiation event management. Lead aprons do not provide effective protection
against the higher-energy radionuclide emissions likely to be encountered with
radioactive contamination.