Re: Structural radiation protection for 64 slice CT

[garyi@trinityphysics.com]

The collimation may have some small effect on the sheilding, but its not significant, 

certainly not double.  The shielding depends primarily on how much scanning the CT 

will do.  Its easy to make a mistake about the shielding if you use a pat workload of 

20,000 or 30,000 mAmin/week, because the workload has to account for the slice width 

quoted in the scatter plot.  You can see this if you think about sheilding a CT for 

scanning exclusively in 5 mm/rotation mode, and compare that to sheilding the same 

patient workload done exclusively in 10 or 20 mm/rotation mode.



Thats assumming that other scanner characteristics are equivalent.  For example, if the 

particular scanner uses less sensitive detectors that require more radiation, then of 

course the scattered radiation will be larger.  



For the 64 slice CT, the scatter radiation at a given instant will definitely be higher, but 

the weekly dose to a nearby point will only increase if the patient workload increases.  

Since the 16 slice scanners are already very fast, patient throughput is limited by factors 

other than scan speed and can not increase much.  



-Gary Isenhower



On 1 Dec 2004 at 9:31, Irvine, Michael <Michael.Irvine@health.wa.gov.au> wrote:



> 

> I have a query regarding the shielding implications of 64-slice

> scanners. With a larger maximum collimation opening and higher maximum

> tube current they obviously can potentially have a much higher

> radiation output than earlier scanners but my question is: do they in

> reality? I've seen a recent shielding assessment that was performed

> using the scatter dose data provided by the manufacturer for their

> 64-slice scanner (obtained with maximum factors) which determined that

> the shielding required (about 3mm lead) was more than double that

> required for a 16-slice scanner. One last question is: with much

> faster scan times and the subsequent ability to examine more patients

> per week, should workload figures used in calculating the shielding

> requirements be increased? Thanks in advance, Mike. Mike Irvine

> Radiation Health Branch Department of Health, WA Tel: (08) 9346 2260

> Fax: (08) 9381 1423 The contents of this e-mail transmission are

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