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Re: X-ray shielding recommendations
>I will let Drs. Archer or Simpkin address question 1 and will tackle
>questions 2 and 3.
>
>NCRP 49 is in the process of being revised. When it is published it will
>address the 100 mrem per year shielding requirement. Until that time,
>shielding to the requirements in NCRP 49 will be adequate. The revision of
>NCRP 49 will clearly indicate that rooms shielded prior to publication of
>the revision will be considered adequately shielded if they meet NCRP 49,
>i.e., you will not have to worry about 100 mrem/year until the revision is
>published.
>
>Mammography will also be addressed in the revision. I would like to add
>some observations and comments regarding the need, or lack thereof, for
>shielding mammography rooms. Most mammography rooms will not require
>shielding in addition to the conventional two layers of gypsum drywall used
>in wall construction. The volume irradiated is very small with only small
>amounts of scatter. The patients body shields in one direction since
>virtually no 25 kVp radiation is going to get through the patient. The
>lead glass or lead acrylic shield (that the tech stands behind) shields in
>another direction. The mammography equipment itself provides shielding in
>yet another direction. The film holder intercepts almost all primary
>radiation so there is no need for a primary barrier. Gypsum drywall has a
>high calcium content which is very effective in absorbing radiation at
>mammographic energies.
>
>The only area for concern would be the door, since wood doors do not absorb
>much radiation relative to gypsum drywall. However, if the mammographic
>unit is placed so that the patient has her back to the door then this will
>not be a problem.
>
>Befor you ask, the revision of NCRP 49 will probably not be available
>before 2001 since it must undergo NCRP critical review, NCRP Council
>review, AAMP Diagnostic Committee review, and AAPM Science Council review.
>(I am sure I have overlooked someone that must review it!)
>
>
>Joel E. Gray, Ph.D., Consultant
>2804 Second Street Southwest, Suite 334
>Rochester, Minnesota 55902
>
>Business Phone 507-269-4247
>Fax 507-286-8910
>Home Phone 507-286-8910
>e-mail joelgray@sprynet.com
>
>
>At 6:45 PM -0500 1/27/00, Harold Prussia wrote:
>>1. My question is how do I determine lead equivalence of a X-ray barrier
>>made up of combined concrete and steel. I am doing a shielding
>>calculation for a R/F room that has occupancy above it. The floor
>>between the two areas has 3 inches of concrete and an 18 gauge steel pan.
>> One of the main references I am using is "Attenuation Properties of
>>Diagnostic X-ray Shielding Materials" by Archer, Fewell, Conway, and
>>Quinn, Med. Phys. 21 (9), September 1994 which provides lead equivalence
>>for both materials. My concern is that the beam hardening of the steel
>>will change the effective lead equivalence of the concrete.
>>
>>2. I use to use the "free ware" KUX and CALKUX by D.J. Simkin, as a
>>double check of my calculations, but, my 1989 version uses the NRCP 49
>>limits instead of the newer suggested limits of 100 mRem/year (1
>>mSv/year). Does anyone know of reasonable priced shielding software that
>>calculates using the new limits?
>>
>>3. I am also looking for mammography room shielding references. I am
>>working with an experienced "medical" Architect that claims he always
>>designs mammography rooms with normal room construct of drywall. My
>>personal preference has been to use 1 mm of lead or to use four layers of
>>drywall with staggered joints to ensure that the minimum drywall
>>thickness was at least 1 inch. But I thought I better, sharpen my
>>pencil, and rework the calculations in case I need to justify my
>>requirement for shielding the mammography rooms.
>>
>>I look forward to any helpful comments.
>>
>>
>>
>>
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