RE: Leakage radiation for panoramic dental x-ray

["Parry, Don (CIS)" <dparry@michigan.gov>]

To be conservative, you could assume a leakage of 100 mR/hr at 1 meter at the leakage technique factors... which the manufacturer would provide... these are the tube ratings that the machine could operate at continuously... for a regular radiographic tube this may be something like 150 kVp and 3.3 mA... for a panoramic dental tube it would be lower.  According to an NCRP draft report on Dental x-ray protection, tube heads designed for panoramic radiography typically shield leakage radiation at a leakage technique of 100 kVp, 15 mA and a duty factor of 1/20... that would be equivalent to 100 kVp and 0.75 mA continuous operation....leakage would be lower at lower kVps... both because the output is lower and also because the housing will shield a larger fraction of the lower energy beam.  It is likely that many Panoramic tubes are designed to have much less leakage than the legal limit, but they would not be compelled by regulation to do so. 



Measurements of scatter and leakage radiation combined are generally done during our inspections. Measurements are performed at the operator position (6-10 feet away) and at clinical settings (80-90 kVp and 4-8 mA) for Pan units.  The rate will of course vary as the beam swings around, but I can seldom remember measuring more than a few mR/hr instananeous rate at these settings and distances.  This would be with no patient or cassette in the beam.



Don



Donald E. Parry, CHP

Health Physicist

Michigan Department of Consumer & Industry Services

Radiation Safety Section

Phone : 517-241-1989  Fax: 517-241-1981

mailto:dparry@michigan.gov

www.michigan.gov/bhs 



-----Original Message-----

From: Sandy Perle [mailto:sandyfl@EARTHLINK.NET]

Sent: Thursday, May 22, 2003 10:47 AM

To: Miltos Tsiakalos; radsafe@list.vanderbilt.edu

Subject: Re: Leakage radiation for panoramic dental x-ray





On 22 May 2003 at 15:11, Miltos Tsiakalos wrote:



> Should I consider the leakage radiation limit for such

> a machine at 100 mR/h at 1 m ,as for the usual x-ray

> machines or do you believe that this is a high value ?



I'd be shocked if the tube leakage approaches anything what you're 

proposing. I'd expect it to be a very small dose rate, even at 

contact, negligible at 1 m.

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