Re: Iodone Therapy Dose Calculation

["Charles Meyer" <cmeyer@brc1.tdh.state.tx.us>]

> Date:          Tue, 25 Nov 1997 11:46:15 -0600 (CST)
> Reply-to:      radsafe@romulus.ehs.uiuc.edu
> From:          "Charles Meyer" <cmeyer@brc1.tdh.state.tx.us>
> To:            Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject:       Re: Iodone Therapy Dose Calculation

> 
> > >
> > >>I am curious to see if anybody has looked into this before:
> > >>
> > >>For calculating the external dose to general public from iodine therapy
> > >>patients, the NRC Regulatory Guide 8.39 (released April 97), makes a
> > >>conservative assumption that in the first 8 hours after administration, 80%
> > >>of the iodine is removed from the body only through its physical decay
> > >>(page 16).  It then proceeds to an equation that includes the first 8 hour
> > >>physical decay of 80% of radioiodine and the dose from the thyroidal
> > >>and extra-thyroidal radioiodine uptakes (100%) from 8 hours to infinity
> > >>(Equation B-5, page 16).
> > >>
> > >>The question that I have is what does happen to the 20% of the original
> > >>administered iodine in the first 8 hours?! It does not show up in Equation
> > >>B-5.  The contribution from the missing 20% does not seem to be
> > >>substantial (a few tens of mrem for most patients), but it can make a
> > >>difference if you are right around 500 mrem limit.
> > >>
> > >>Thanks in advance for your comments.
> > >>    Ehsan Samei, PhD
> > >>    Department of Radiology
> > >>    Henry Ford Health System            313-876-2245 voice
> > >>    2799 W Grand Blvd                   313-876-7925 fax
> > >>    Detroit, MI 48202                   samei@rad.hfh.edu
> > >
> > >Dear Ehsan
> > >
> > >I think the NRC calculation may be a bit simplistic. It is possible to
> > >carry out much more realistic modelling.
> > >
> > >We use an EXCEL spreadsheet package we've developed to calculate the
> > >exposure of other persons from the patient , based on activity
> > >administered, clearance rates, the radiation dose to other persons you are
> > >willing to tolerate, and  probable patterns of close contact. Decisions
> > >relating to the discharge of such patients and advice to be given (eg
> > >relating to travel by public transport , contact with young children,
> > >return to work etc) are based on this, and the probable exposures
> > >documented.Where there is a particular concern with the larger therapeutic
> > >doses, we actually measure individual patient exposures and clearance rates
> > >and factor these in - this can be quite important, as there is a large
> > >variation between patients.
> > >
> > >This package is freely available. If you are interested in a copy, let me
> > >know.
> > >
> > >Cheers
> > >
> > >John Cormack
> > >
> > >
> > >_____________________________________________________
> > >John Cormack
> > >Chief Hospital Scientist
> > >Division of Medical Imaging
> > >Flinders Medical Centre
> > >Bedford Park
> > >South Australia 5042
> > >
> > >Ph:08-8204-4642 National, 618-8204-4642 International
> > >Fax:08-8204-5450 National, 618-8204-5450 International
> > >
> > 
> The physical half life for I-131 is 8 days, f1=1, and the fractional 
> uptake for the thyroid is 0.3, leaving 0.7 to the whole body with an 
> effective half life of 12 days.  Go figure. 
> <><><><><><><><><><><><><><><><><>            
> <>    Charles R. (Russ) Meyer                  <>
> <> Email: cmeyer@brc1.tdh.state.tx.us           <> 
> <>     Phone:(512)834-6688                       <>
> <>        Fax:(512)834-6654                        <>
> <><><><><><><><><><><><><><><><><>
>Whoops,  other 0.7 goes directly to excretion.  Organic remains with 
an effective half life of 12 days. 
<><><><><><><><><><><><><><><><><>            
<>    Charles R. (Russ) Meyer                  <>
<> Email: cmeyer@brc1.tdh.state.tx.us           <> 
<>     Phone:(512)834-6688                       <>
<>        Fax:(512)834-6654                        <>
<><><><><><><><><><><><><><><><><>