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RE: Thyroid radiation doses are much too high



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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