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07 October 2008

Answer to Question #4927 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Equipment

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

With reference to a stuck source in a teletherapy device, I understand from the answer to question #4235 that the maximum amount of scatter radiation at one meter from the patient is 0.6 percent of the incident radiation beam. Are there any references indicating the dose rate at one meter from isocenter without a patient present?

Further, are there any references indicating the average dose to the servicing person returning a stuck source to the fully shielded position using a T bar tool?

Although the amount of scatter would be lower without the patient present, it can be assumed for radiation safety purposes that the maximum amount of scatter radiation is the same (0.6 percent of the incident radiation beam).

The best reference regarding dose to a service person from a stuck source would either be a source vendor or a service company that is authorized to service teletherapy units. The amount of exposure would vary depending on the current source activity (and subsequent beam output), whether or not the jaws are closed on the unit, and the location of the service person.

Ken "Duke" Lovins, CHP

Reference
Personal conversation with John Freshcorn, MS

Answer posted on 17 November 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.