There are important differences between radiation exposure and contamination with radioactive material. A basic understanding of each is critical for effectively triaging and managing patients.

This section will provide a brief overview of radiation concepts relevant to using medical countermeasures for internally contaminated patients. But I encourage you to watch the supplemental video clip in this section for an example of how these concepts can be explained to your patients and staff. An even more comprehensive overview of radiation basics can be found in the additional resources section.

Radiation is a type of energy, or electromagnetic wave, that originates from a source, like a radioactive atom, and travels through space. The electromagnetic spectrum ranges from low energy forms of radiation like radio waves, to high energy forms like gamma rays. We define ionizing radiation as any type of radiation that has enough energy to ionize atoms. Ionizing radiation causes health effects and injuries by damaging biological molecules like DNA, proteins, or cell walls. Different types of ionizing radiation include alpha particles, beta particles, neutrons, x-rays, and gamma rays. Each type of ionizing radiation has unique properties that determine the distance it travels from its source and its ability to penetrate other objects or tissues.

To illustrate the difference between radiation exposure and contamination with radioactive material, imagine a woman receiving a typical chest x-ray. The patient is exposed to a source of ionizing radiation that passes through her body to a detector. She has been exposed to radiation, but there is no radioactive material on her so she has not been contaminated. There are two types of contamination to consider. External contamination occurs when radioactive material is deposited on a person’s body, typically on hair, clothing, and exposed areas of skin. Internal contamination occurs when there is an intake of radioactive material via inhalation, ingestion, injection, or through an open wound. After inhalation, radioactive material can be exhaled, deposited in the large and small airways depending on particle size, transported by ciliary movement to the gastrointestinal tract, or absorbed into the systemic circulation. After ingestion, radioactive material can be deposited in different parts of the gastrointestinal tract, absorbed into the bloodstream, or eliminated in stool. The distribution of different radioactive materials in the body will depend on the chemical form of the material. For example, after absorption into the systemic circulation, radioactive iodine will deposit in the thyroid gland.

So, when someone has internal contamination, the radioactive source is now held within the body, and an internally contaminated patient is constantly being exposed to radiation by that source. This exposure will continue until the radioactive material is eliminated from the body.

Radioactive material is removed from the body through a combination of natural radioactive decay and biological excretion processes. Radioactive decay is measured in physical half-lives, which is the amount of time it takes the material to reduce the amount of radiation it emits by half. Similar to this concept, a material’s biological half-life is the rate at which the body eliminates half of the internalized amount. You can think of the biological half-life as being equivalent to the elimination half-life of a drug. Because radioactive material is removed through a combination of radioactive decay and biological elimination, each radionuclide will have a specific so-called “effective half-life” that is shorter than both the physical and biological half-lives.

A primary benefit of some medical countermeasures is the ability to facilitate removal from the body by blocking the incorporation of radionuclides into tissues, or by binding to the material so that it is excreted more rapidly. This reduces the amount of exposure time to the radioactive source inside the body, and therefore reduces the total radiation dose from the source. Additionally, some countermeasures provide benefit by supporting the regeneration of cells damaged by high doses of radiation.

While medical countermeasures may be useful for reducing harm from internal contamination, there are some limitations:

1. There are only a few types of medical countermeasures, and they only work for specific radionuclides. There is no single medication that is effective in treating all radioactive contaminants.

2. Medical countermeasures are more effective when given early on following exposure or contamination; sometimes they are most effective if given prior to exposure. Extended delays in treatment can significantly lower the effectiveness of a medical countermeasure.

3. There may be limited amounts of medical countermeasures available, and you may not know who needs them early after an incident.

Therefore, a person with internal contamination who would benefit from medical countermeasures should be treated as quickly as possible in order to reduce the radiation dose and damage their body receives from the radioactive material. It is also important to note that radioactive material is excreted in a person’s urine or feces, which is therefore contaminated and should be handled with the appropriate precautions when it is transported, tested, or disposed.