Communicating Radiation Exposure: A Simple Approach

• radiation exposure
• effective dose
• background equivalent radiation time

One of the difficulties nuclear medicine physicians and technologists often encounter is how to explain the radiation dose from nuclear medicine procedures to patients. It appears there is no standardized explanation regarding radiation exposure in most nuclear medicine departments, and some physicians and technologists simply avoid the topic. In this article, a simple explanation of radiation exposure is given by using the concept of effective dose and the natural background radiation exposure. The concept of effective dose (previously called effective dose equivalent) was created by the International Commission on Radiological Protection in 1977 in an attempt to supply a relative risk of radiation exposure for nonuniform exposure by taking into account the type and energy of the radiopharmaceutical and the sensitivity of each organ to radiation (1). For example, neutrons are thought to be more detrimental than photons and thus are given a higher value of effective dose. Among the organs and tissues, gonads are more sensitive than other organs and have a higher weight in effective dose. The effective dose is intended to provide a single-value estimate of the overall stochastic risk (i.e., the total risk of cancer and genetic defects) of a given irradiation, whether received by the whole body, part of the body, or 1 or more individual organs. An extensive review of the concept and the calculation of effective dose can be found elsewhere (2,3). The use of the effective dose concept facilitates communication between professionals but is difficult for patients to comprehend. Recently, attempts have been made to compare radiation exposure from radiographic procedures with the background equivalent radiation time (BERT) (4). For instance, if we assume that the average background radiation is 3 mSv annually and a routine chest x-ray gives an effective dose of 0.08 mSv, then the radiation from a chest x-ray is equivalent to 10 d of radiation exposure from nature. In our approach, instead of telling a patient that he or she has received 7 mSv of radiation from a bone scan, we could explain to the patient that radiation exposure from the bone scan is equivalent to 2 y of radiation from nature.

Although the background radiation rate varies significantly from 1 geographic area to another, the average natural exposure rate in the Unites States is approximately 3 mSv/y, including contributions from cosmic, terrestrial, and internal exposures. The biggest source of natural background radiation is radon gas, which seeps into the basement of houses from rocks underground and contributes 2 mSv/y in the United States (5,6). Table 1 provides examples of variations in natural background radiation in a few areas in the United States.