Re: I-131 and Dialysis

[carol marcus <csmarcus@ucla.edu>]

At 08:25 AM 2/1/99 -0600, you wrote:
>We have a dialysis patient who the
>endocrinoligist would like to give 10
>mCi of I-131.  I'd like to hear from
>anyone with experience as to
>synchronization of dose with the
>dialysis procedure and special safety
>procedures.
>
>Thanks.
>
>--
>Chris Hawkins
>Radiation Oncology
>Guthrie Clinic - RPH
>Sayre, PA   18840
>570.882.4048 or 570.882.5166 (fax)
>mailto:chawkins@inet.guthrie.org
>
>
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>Dear Chris:

I would recommend dialysis 24 hrs. after administering the dose.  In a
euthyroid patient, this would represent 3 halflives for the non-thyroidal
fraction.  In a hypothyroid patient, this would represent about 2 halflives.
In hyperthyroid patients, it would be >3 halflives, but I'm not sure how
much greater.

The dialysis kit is disposable, so contamination is not an important issue.
The huge quantity of water flowing through generally reduces the residual
I-131 in the disposable set to next to nothing.  However, a lot of
regulators make a living regulating "next to nothing", so check it and decay
it out if necessary.  No other part of the dialysis equipment will be
contaminated.  The I-131 goes directly to the sewer, where it would go if
the patient had normal renal function.

The radiation dose from the patient to other patients and nursing staff is
negligible, so no precautions are needed.  With thyroid cancer therapy doses
of 100 or 200 mCi, one should restrict the patient according to the 500mrem
limit.  There is a regulation that a nurse MUST be in the same room as the
patient during the entire dialysis procedure.  I have blithely informed the
nursing staff that the Atomic Energy Act supercedes this rule, and that a
nurse may observe a highly radioactive patient through a glass window in the
door in order to comply with ALARA. While this claim is of course
unsubstantiated, no one has contested it yet because it seems like a
reasonable way to satisfy both requirements.  

The last issue is how many dialysis treatments are necessary to dialyze off
all the non-thyroidal fraction.  My rough estimates are that the first
dialysis gets off about half and that subsequent dialyses get off 1/2 to
1/3.  In patients with renal failure, more I-131 may be excreted through
stool than in patients with normal renal function, and this I-131 of course
cannot be touched by dialysis. Empirically, therefore, I recommend 3
dialysis treatments on successive days, beginning 1 day after dose
administration.

Ciao, Carol

Carol S. Marcus, Ph.D., M.D.
Harbor-UCLA Medical Center

<csmarcus@ucla.edu>

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