RE: Medical Doses

[Karin Gordon <KGordon@exchange.hsc.mb.ca>]

For diagnostic studies, nuclear medicine departments commonly use short
half-life gamma emitters with no or minimal  beta emissions, in order to
keep the radiation dose to the patient ALARA.  The most commonly used
radioisotope is Tc-99m (140 kEv gamma, 6 hour T1/2) which is labelled to
various pharmaceutical compounds, each of which will a different
biodistribution, retention/excretion pattern, depending on  type of
procedure. There are various types of NM diagnostic procedures,  used to
examine the physiological function (uptake and clearance rates) of
specific organs and often to obtain images of these organs and tissues.
Tc-99m is labelled to at least 10 different pharmaceuticals, each of
which will have an very unique biodistribution pattern within the body.
Of course, there are other isotopes used: most commonly Tl-201, Ga-67,
In-111, Xe-133, and I-131 for diagnostic procedures;  the list of  most
common therapeutic  isotopes includes I-131, P-32, Y-90, Sr-89  (all
beta particle emitters).

The radiation dose the patient receives is directly proportional to the
amount of radioactivity in the radiopharmaceutical administered - so the
 EDE is normally expressed in mSv/MBq of the specific
radiopharmaceutical administered.  Check out the ICRP portion of your
bookshelf:  

ICRP Publication 53: Radiation Doses to Patients from
Radiopharmaceuticals, which gives organ&  tissue doses and  EDE doses (
based on the old tissue weighting factors).  

ICRP Publication 62  which includes "Addendum 1 to Publication 53 -
Radiation Dose to Patients from Radiopharmaceuticals".  This publication
gives the recalcuated EDEs, based on the ICRP-60 tissue weighting
factors. 
In Canada, we are adopting most of the recommendations of ICRP-60,
including most of the dose limits and the tissue weighting factors - so
we use ICRP-62 to determine EDE from administered radiopharmaceuticals.

Generally, North American  NM departments tend to administer larger
amounts of radioactivity for diagnostic studies than do their British or
European counterparts. 

Walter Huda and I published a paper in Health Physics in March 1989
Volume 56- pp 277-285 entitled Nuclear medicine staff and patient doses
in Manitoba (1981-1985) which gave the EDEs (pre ICRP-60) for typical
nuclear medicine procedures. That paper is a bit dated now,  and some of
the radiopharmaceuticals have changed since, but it will give you an
idea of typical EDEs from diagnostic NM procedures.

Hope this is helpful

Season Greetings to all RadSafer colleagues, and may we all pray for
peace given the season and current world events.

************************************************************************
************************
Karin Gordon
Radiation Safety Office
Health Sciences Centre
GC-214, 820 SherbrookSt.
Winnipeg, Manitoba
CANADA  R3A 1R9

KGordon@hsc.mb.ca           or        KGordon@cc.UManitoba.ca

phone (204) 787-2903
fax      (204) 787-1313





 
>----------
>From: 	Jim F. Herrold[SMTP:Herrold@uwyo.edu]
>Sent: 	December 18, 1998 10:37 AM
>To: 	Multiple recipients of list
>Subject: 	Medical Doses
>
>RADSAFERS
>
>Is there a WEB site or other central location that lists examples of
>effective doses patients receive from therapeutic or diagnostic uses of
>radioactive materials. Obviously, I could go do a search on the network, but
>time is tight and I am hoping someone out there has a favorite site (or
>sites).
>
>As always, I appreciate the responses I get. 
>
>Jim Herrold
>Radiation Safety Officer
>University of Wyoming
>
>herrold@uwyo.edu
>************************************************************************
>The RADSAFE Frequently Asked Questions list, archives and subscription
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