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CT Radiation Dosing Calculations

Dr Timothy Hardcastle dr.tchardcastle at absamail.co.za
Thu Oct 15 20:14:02 BST 2009


Ken et al

I have been silent for a while now, but I feel it is time to comment.
Firstly let me remind everyone that I am all for good clinical medicine
and come from a place where we are often forced to use clinical judgement
and hope for the best.

However, I think that the experience I have recently gained from dealing
with many more blunt trauma cases where plain films were often done prior
to referral to our unit, where we will liberally use full body trauma
scan, with a 128 slice scanner. The number of clinically relevant
additional injuries in our subgroup of severely injured patients (our
admission average ISS is 24 and NISS is 36) are sufficient to justify such
scans. These patients are almost all sedated, intubated and ventilated,
which complicates clinical assessment. These patients have a significant
risk for missed injury - which by liberal scanning we have reduced to
under 2%. The more modern scanners use less radiation for the same quality
of scan - mostly even better than the older generation of scanners. It is
all about risk-benefit and these patients - ISS >16 and BLUNT trauma or
transmediastinal penetrating trauma are best served by early comprehensive
imaging - as a one-stop shop, rather than numerous segmental scans.

Secondly, the patient must SURVIVE the trauma and the hospital stay to get
to the point where they can get their ALL or lymphoma. If we look at the
missed injury with blunt trauma (particularly missed bowel injury) - with
associated poor outcomes, the increased survival is enough to justify the
risk.

Finally though - quality control of the technical issues and of the
appropriate use of the scan - i.e. not for the fully conscious, evaluable
patient, is essential. Most penetrating trauma should NOT be undergoing
scan - exceptions transmediastinal and maybe RUQ GSW. Not for stabs, or
other GSW's

On the issue of CT as an angio device - fine for blunt arch / vessel
screen. For anything else use a catheter directed angio! The miss rate for
other injury is just too high.

My 2c
Dr T C Hardcastle
M.B., Ch.B. (Stell); M. Med. (Chir) (Stell); FCS (SA)
Principal Specialist Trauma Surgeon /
Honorary Lecturer University of KwaZulu-Natal Dept Surgery
Deputy Director - IALCH Trauma Service
Durban - South Africa

> I am very aware that Ionizing radiation dosing from radiotherapy, CT
> scanning, arteriography, C-Arm imaging in the OR, cardiac catheterization,
> and
> trauma injury screening and diagnosis has historically been administered
> most
> of  the time in a professional and standard manner.   I am also aware that
> each of these modalities has had its miscalculations and subsequent injury
> to  patients as well as to health care workers at all  levels.       The
> recent experience reported by  many sources of a hospital in Los Angeles
> was
> one such mis  calculation.      However, I am aware that such  "accidents"
> often lead to regulatory agencies using such an incident to now  inspect
> hospitals who have never had a known similar miscalculation.    While
> making a
> visit, they very often raise questions of relivance, indication,  and use
> of
> imaging, or whatever has brought them to the  facility.    Following the
> announcement earlier this week of the  miscalculation, I did a quick check
> among
> patients in this hospital and sought  information from many of my
> colleagues
> at other hospitals. That led to my  earlier post regarding guidelines for
> ordering imaging, how images are often mis  used and lead to inappropriate
> decisions, and other issues.    It  was to raise the awareness of all of
> us
> regarding the use of a modality that we  all have over used.
>
> k
> --
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