Answer to Question #4929 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — PET

The following question was answered by an expert in the appropriate field:

I was once in a hospital and by accident I walked into the room where they were starting a PET/CT scanner. Can you tell me how much radiation I received and how dangerous this is? Did I receive more than the patient on the scanner?

It is difficult to quantify radiation dose for you without having measured the output of this particular unit and without knowing what mode the unit was operating in (PET [positron emission tomography] or CT [computerized tomography]—the unit only operates in one mode at a time, and I assume you were not in the room long enough for the entire patient procedure). Also, I have no information on your distance from the scanner, the amount of time you were in the room, and your location relative to the gantry (geometry). Suffice it to say that if you were in the room for a short period of time (i.e., seconds), you may have received a small amount of radiation dose in the form of scatter radiation from the CT portion of the unit and/or a small amount of radiation dose from the patient if the patient had received the radiopharmaceutical from the PET portion of the procedure (in the PET mode, the unit does not emit radiation, instead the radioactive material is injected into the patient and is detected by the PET scanner).

Typically, the scatter radiation doses away from the patient are only a fraction of a percentage of what the patient receives, so it is very likely that the radiation dose you received was very small.

Although the radiation dose to an individual walking into an x-ray room may be small, there are certain requirements and safeguards that are in place to protect these individuals and to keep their radiation dose as low as reasonably achievable (ALARA). You should have seen warning lights and/or warning signs. In addition, if you are frequenting an x-ray area, you should receive basic radiation safety instructions so that you will know not to walk into an x-ray room unless you are sure that the unit is not producing radiation.

Ken "Duke" Lovins, CHP

Answer posted on November 17, 2005. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.