Fwd: Exposure rate measurements for fluoro.

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>From: Robert A Scott <bobscottchp@JUNO.COM>
>
>         I have been reviewing 21 CFR 1020.32 regarding exposure rate
>measurements of fluoro equipment.
>
>         We all know that the measurements for a certified mobile C-Arm 
> are to be
>made at 30 cm from the surface of the II.  And we also know that for a
>regular C-Arm (not for specialty exams) the SSD may be no less than 38
>cm.  We also know that C-Arm's equipped with AERC shall not be operable
>at an exposure rate greater than 10 R/min where the useful beam enters
>the patient.
>
>         Now, if we must make the measurement at 30 cm from the II, but 
> the II in
>some C-Arms is fixed so that the SID may be in the range of 80 - 90 cm,
>then accepting a dose rate of maybe 8 R/min at 30 cm from the II really
>means the dose could be as high as 18 R/min or more at a distance of 38
>cm from the source.  The way I read the regulations, even though one must
>make the measurement at 30 cm from the II, it doesn't change the fact
>that the regs limit the exposure rate WHERE THE BEAM ENTERS THE PATIENT
>to 10 R/min or less.
>
>         So how is this issue resolved?
>
>Bob Scott, CHP
>Roger Williams Medical Center
>Providence, Rhode Island
>bobscottchp@juno.com


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