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RE: Thyroid radiation doses are much too high
At 02:22 AM 3/9/2004, Cheng Kit-man wrote:
>The optimal treatment is to suppress the function of the thyroid so that
>secretion of thyroid hormones returns to the normal levels. The thyroid is
>still functional after the treatment and the patient does not need to rely
>on medication.
>
>However, present treatment regimes apply a standard I-131 dose irrespective
>of the level of hyperactivity and size of the thyroid. In most situations,
>the thyroid function is over suppressed and the patient will rely on hormone
>supplements for the rest of the life. The benefits are that the dose
>prescription is simplified, hospitals do not need to stock and dispense
>liquid I-131, the standard doses can be fabricated into tablets by mass
>production at a remote centralized radiopharmacy and workers exposure can be
>reduced. The costs are that the patients are treated for hyperthyroidism to
>become hypothyroidism and the excess radiation dose may increase the risk of
>developing thyroid cancer later in life.
>
>Clement
>
>-----Original Message-----
>From: owner-radsafe@list.vanderbilt.edu
>[mailto:owner-radsafe@list.vanderbilt.edu] On Behalf Of Neil, David M
>Sent: Tuesday, March 09, 2004 6:23 AM
>To: John Jacobus; Stabin, Michael; radsafe@list.vanderbilt.edu
>Subject: RE: Thyroid radiation doses are much too high
>
>A question, re the discussion of Graves disease. If the objective is total
>removal of thyroid tissue, wouldn't the protocol likely be surgical removal
>of the gland, with radioiodine given after to ablate any stray tissue?
>
>This would seem to be both more efficient and more in line with ALARA.
>Given the nature of this group, total ablation with radioiodine sounds like
>the old maxim "To a person with a hammer, every problem looks like a nail"
>
>Does anyone out there have solid information?
>
>Thanks,
>Dave Neil
>
>-----Original Message-----
>From: John Jacobus [mailto:crispy_bird@YAHOO.COM]
>Sent: Monday, March 08, 2004 12:02 PM
>To: Stabin, Michael; radsafe@list.vanderbilt.edu
>Subject: RE: Thyroid radiation doses are much too high
>
>
>Mike,
>Thanks for the reply. My comments were toward trying
>to understand the logic behind the risk in the paper
>under discussion, not it the specifics assoicated with
>your calculations. In reviewing your comments I
>realized I may not have been that clear.
>
>Basically, what I was trying to say is that if we
>remove the thyroid for the computed EDE, as you
>suggest and I forgot to mention, then the risk to the
>other tissues (as such) is only a few rem. Again,
>there is not demonstrated risk below 10 rem.
>
>--- "Stabin, Michael"
><michael.g.stabin@Vanderbilt.Edu> wrote:
> > >I think the risk comes from secondary cancers from
> > other organs, not
> > thyroid cancer. If you give a patient 30 mCi of
> > I-131, the effective
> > dose equivalent is 1170 mrem. See "Radiation Dose
> > Estimates for I-131
> > Sodium Iodide" in
> > http://www.orau.gov/reacts/DOSETABLES.doc
> >
> > John - two problems with this calculation. First,
> > the quantity effective
> > dose should not be used in therapy applications.
> > Second, this effective
> > dose is dominated by the thyroid contribution (340
> > mSv/MBq x 0.03 = 10.2
> > mSv/MBq, and the ED is 11 mSv/MBq, or 39 rem/mCi, as
> > you used). If the
> > thyroid is ablated, as the discussion has assumed,
> > this contribution is
> > removed. However, again, this calculation does not
> > make sense in a
> > therapy situation.
> >
> > 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
> > Pager (615) 835-5153
> > e-mail michael.g.stabin@vanderbilt.edu
> > internet www.doseinfo-radar.com
> >
>
>
>
>=====
>+++++++++++++++++++
>""A fanatic is one who cannot change his mind and won't change the subject."
>Winston Churchill
>
>-- John
>John Jacobus, MS
>Certified Health Physicist
>e-mail: crispy_bird@yahoo.com
>
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This is medical nonsense. First, the natural course of Graves' disease is
hypothyroidism due to intrinsic destruction of the thyroid from
inflammation, if the hyperthyroidism doesn't kill the patient first from
cardiac complications. Second, it is definitely not desirable to leave any
thyroid tissue intact after surgery or radiation, as this tissue will often
grow and cause hyperthyroidism again. An appropriate "calculated dose" is
a dose necessary to kill the gland, not part of it. Third, the
nonradioactive drugs used to suppress thyroid function are dangerous, and
can cause permanent kidney destruction, bone marrow suppression, and
occasional death. A hefty dose of NaI-131 to burn out the entire thyroid
gland is the goal of appropriate medical treatment, not a consequence of
"one size fits all" sloppiness. Nonradioactive drugs for thyroid
suppression are commonly used for a short time to deplete the gland of
thyroid hormone so that when NaI-131 destroys the tissue, toxic levels of
thyroid hormone are not released. And fourth, after 60 years of studying
these patients and finding no evidence of radiation-induced cancer, I think
that it is grossly misleading to suggest that the I-131 "might" cause cancer.
Carol S. Marcus, Ph.D., M.D.
csmarcus@ucla.edu