CT shielding: warning about AAPM Rep. 39 transmission and workload

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

>X-Sender: dsimpkin@mail.execpc.com (Unverified)
>Date:         Mon, 11 May 1998 12:27:27 -0500
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>From: Douglas Simpkin <dsimpkin@EXECPC.COM>
>Subject:      CT shielding: warning about AAPM Rep. 39 transmission and
workload
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
>
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>Simon Downes wrote:
>>We've recently installed our own CT scanner and found the AAPM report number
>>39 (adapted from NCRP report 49) "Specification and Acceptance Testing of
>>Computed Tomography Scanners" combined with the manufactuer's isoexposure
>>contours and maximum exposure rate ("worst case") at one metre from
>>isocentre (usually at 45 deg from the gantry axis) useful for calculating
>>shielding requirements.
>
>I'll warn users that AAPM Report 39 uses transmission data from an early
>paper of mine showing the transmission of primary diagnostic x-ray beams.
>This is propably not hard enough to represent the secondary radiation off
>of a CT scanner. It is therefore probably inappropriate to use the
>transmission data from that report. Again, see Health Phys. 58: 363-367;
>1990, for a better estimation of the transmission of CT secondary
>radiation. (For example, the transmission through a typical 1.6 mm Pb
>barrier is ~50% higher with the values from the CT paper than from AAPM
>Report 39.)
>
>Also, be wary of the recommended workloads in AAPM Rep. 39, as the number
>of slices per patient achieved with modern helical scanners tends to be
>50-100% higher than what was seen with single slice scanners.
>Douglas J. Simpkin, Ph.D.
>Certified Radiation Physicist
>St. Luke's Medical Center
>2900 West Oklahoma Avenue
>Milwaukee, WI 53215
>(414)649-6457
>fax:(414)649-5061
>email: dsimpkin@execpc.com
>