TOPIC 8: Monitoring Internal Dose

Let’s explore Monitoring Internal Dose.

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BIOASSAYS are the method of obtaining information about the amount of uptake of radioactive materials in the body.

The most common method is obtaining a urinalysis and analyzing for any radioactive materials that have been ingested or inhaled into the body and processed out through urine.

The second is by obtaining direct readings of particular organs that may be targets for the radioactive materials.

A typical example would be taking a reading of the human thyroid directly from the outside of the body if the user handles volatile radioactive iodine.

In this case, it is important to use a “phantom” with the approximate density of the human body. With a check source that has similar gamma energy as the radioactive iodine, place it in the “phantom” and take a direct measurement to establish the exposure rate from the phantom.  Then, using the same low background area, count the thyroid at the same distance to determine the exposure rate from the individual.  Calculations can then me made as to the dose received.  These calculations are determined after knowing what kind or radionuclide, its volatility, how much is used at any one time and whether it a particulate or vapor.

This method cannot readily quantify the amount of a Committed Dose Equivalent.  That is performed by more sophisticated methods.