Re: Iodone Therapy Dose Calculation

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

The ICRP halftime of removal from the stomach is 0.5h, so to lose 80% of the
administered activity within the first 8h is obviously highly unlikely
without a massive hemorrhage, or an emesis shortly after swallowing the
dose. Patients given 100mCi doses can usually be released to meet the 30mCi
rule on the day ffollowing the administration.

chris alston

At 11:00  11/25/97 +1030, you wrote:
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>>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
>