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Re: I-131 dose to pregnant woman
Warning flags always go up for me when I read that someone "ran the numbers
through a ... program." This implies that the program is treated as a black
box, with blind acceptance of the results. The 3 key questions are:
1. How well is the program validated? Even if the program has the "Good
Housekeeping Seal of Approval" from a reputable group, is it being using within
the range of the validation? (My experience with shielding programs is that the
results may not be valid for dose rates at the surface of the shielding.) Does
the user periodically run test cases to verify that the program has not become
corrupted?
2. Is the input correct for the program requirements (gigo)? Sometimes, the
assumed units or other parameters are not what the user expects. One situation
I've run into is the issue of daughter activity. Some programs default to
calculating daughter activities, while some programs do not include daughter
activities unless the user requests this; e.g., Cs-137 would be treated as a
pure beta emitter. Although this is probably not a factor, here, there could be
other "gotcha's" in the program.
3. If this person is "a very knowledgeable colleague," why did he blindly
accept results that are so unusual?
The opinions expressed are strictly mine.
It's not about dose, it's about trust.
Curies forever.
Bill Lipton
liptonw@dteenergy.com
"Michael G. Stabin" wrote:
> > I've basically no experience in this matter but I was rather struck by
> some of
> > the numbers in this table. The 2.4 rem (24 mSv, ca. 24 mGy) to the uterus
> (and
> > therefore foetus?) seems to agree with what others have suggested. I note
> > however that the thyroid dose is "only" (quotes indicating my uneducated
> > reaction) 2.6 rem, most other organs considered in the program seem to get
> > greater doses. Now my limited education includes the thought that iodine
> is
> > supposed to concentrate in the thyroid and that the purpose of giving
> I-131 to
> > such a patient is to deliver a dose to the thyroid. The numbers produced
> below
> > would seem to suggest that in fact it is not very efficient. Why is this
> so?
> > Anyone care to educate me? (in brief I hope :-) )
>
> In brief, I think the numbers are not very good. The dose to the esophagus
> and thymus are inexplicably high, and dose to the urinary bladder is way too
> low, as is the dose to the thyroid, as you note. Carol Marcus suggests the
> J. Nucl Med article for guidance, and I agree. These are the same numbers
> that I referred you to on the RADAR web page. The article gives doses to a
> number of organs, with dependence on the degree of hyperthyroidism. The dose
> to the uterus is representative of the dose to the fetus in the first few
> weeks of pregnancy.
>
> 20% thyroid uptake
> Urinary Bladder 540 mGy
> Ovaries 20 mGy
> Red Marrow 40 mGy
> Thyroid 200,000 mGy
> Uterus 30 mGy
>
> 40% thyroid uptake
> Urinary Bladder 430 mGy
> Ovaries 20 mGy
> Red Marrow 50 mGy
> Thyroid 400,000 mGy
> Uterus 30 mGy
>
> 60% thyroid uptake
> Urinary Bladder 350 mGy
> Ovaries 20 mGy
> Red Marrow 70 mGy
> Thyroid 550,000 mGy
> Uterus 30 mGy
>
> 80% thyroid uptake
> Urinary Bladder 320 mGy
> Ovaries 15 mGy
> Red Marrow 90 mGy
> Thyroid 660,000 mGy
> Uterus 20 mGy
>
> I rounded these to 1 or 2 sig figs, and took a rough average of the "fast"
> and "slow" thyroid uptake numbers from Table 2 of the JNM article (if you
> want the dose in rads, divide the above numbers by 10). These are just rough
> estimates for a given patient, more specific thyroid dose calculations
> should be done, but they give you an idea of more reasonable numbers for the
> other important organs. I will note, however, that the numbers given in the
> JNM article for fetal dose at later stages of pregnancy are not reliable, as
> fetal uptake has not been considered. See Health Phys 73(5):756-769, 1997
> for better numbers in later pregnancy.
>
> Mike
>
> Michael G. Stabin, PhD, CHP
> Assistant Professor of Radiology and Radiological Sciences
> Department of Radiology and Radiological Sciences
> Vanderbilt University
> 1161 21st Avenue South
> Nashville, TN 37232-2675
> Phone (615) 343-0068
> Fax (615) 322-3764
> e-mail michael.g.stabin@vanderbilt.edu
> internet www.doseinfo-radar.com
>
> ----- Original Message -----
> From: <Peter.Thomas@health.gov.au>
> To: <radsafe@list.vanderbilt.edu>
> Sent: Monday, August 19, 2002 8:21 PM
> Subject: Re: I-131 dose to pregnant woman
>
> >
> >
> > Peter Thomas
> > ARPANSA
> >
> >
> >
> > I took this question to a very knowledgeable colleague who ran the numbers
> > through an internal dosimetry program called RSAC using ICRP 39 model of
> > the human body this is the info he came up with.
> >
>
> >
> >