Re: Thyroid radiation doses are much too high

[John Jacobus <crispy_bird@YAHOO.COM>]

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  



It has not been demonstrated that an EDE of 1.2 rem in

a population causes excess cancers.  Is it possible

that a person with Graves' disease may have some

underlying, excess cancer risk?  I do not think this

has been shown in this subpopulation.  (My

mother-in-law, who died last year at 88 from

complications of a stroke and epileptic seizures, was

treated in the 1950s for Graves' diseasse.)



I think this is another one of those "what if" studies

involving extrapolations of numbers, i.e., what if xxx

patients received yyy doses and the risk is zzz . . .

Like you, I think the risk from untreated Graves'

disease is much greater than that of a projected

cancer risk.



Thanks for the insight.



--- Carol Marcus <csmarcus@ucla.edu> wrote:

> At 07:36 AM 3/7/2004, Fred Dawson wrote:

> >New Scientist reports 6 March that Thyroid

> radiation doses are much too high

> 

> 

> Dear Radsafers:

> 

> I don't understand this thread at all, or maybe I'm

> missing 

> something.  When Graves' disease is adequately

> treated with I-131 NaI, the 

> thyroid gland is gone.  Burned away.  Otherwise, it

> is likely that the 

> Graves' disease will recur.  You can't get cancer

> from tissue that is 

> gone.  You can't get thyroid cancer from adequate

> treatment of Graves' disease.

> 

> Years ago, a friend of mine who is a leading nuclear

> medicine physician was 

> asked what he would do if his service administered

> 20 mCi I-131 NaI to the 

> wrong patient.  He immediately quipped, "I'd give

> him another 20 mCi!"  The 

> idea is to wipe out the gland so that there would be

> no possibility of 

> thyroid cancer in the future. In any case, I-131 is

> very inefficient at 

> causing thyroid cancer.  It appears to differ from

> external beam radiation 

> in this respect.  I-131 induced thyroid cancer is

> 0.05 cases/year/million 

> persons per rem for adults (Maxon HR, Thomas SR,

> Saenger EL, et al.: Amer. 

> Jour. Med. 63:967-978, 1977).

> 

> Soon after I-131 was introduced widely for treatment

> of hyperthyroidism 

> (after WWII), concerns about radiation-induced

> cancer prompted a large 

> study of patients treated for hyperthyroidism with

> I-131 vs. those treated 

> with surgery.  The end point was of course not

> thyroid cancer, but 

> leukemia.  There was no increase in leukemia in the

> group treated with 

> I-131 vs. surgery.  (Thompkins E: Late effects of

> radioiodine therapy. AEC 

> Symp 20, 431-440, 1970).

> 

> A large Swedish study and an FDA study on American

> children given I-131 for 

> diagnostic purposes failed to show any increase in

> thyroid cancer (these 

> patients had thyroid tissue).

> 

> Physicians who give calculated doses of I-131 for

> Graves' disease commonly 

> have to give a second or a third dose to do the job.

>  Some (like me) 

> "doctor up" the parameters for the "calculated

> dose".  Most patients who 

> receive 29.9 mCi (the maximum for outpatient

> treatment determined by NRC's 

> old scientifically unfounded "30 mCi rule") burn out

> their thyroids the 

> first time.  It is because no one has ever

> scientifically credibly 

> documented any deleterious effects from the large

> "one size fits all" doses 

> of I-131 that there are still physicians on both

> sides of the issue.  I 

> have used an initial large dose when it was

> important to get the patient 

> hypothyroid as quickly as possible, and on synthroid

> at that point.  I 

> think that both strategies are valid.  There are of

> course patients who 

> need more than 29.9 mCi, sometimes much more, but

> that is another 

> issue.  For these patients, calculated doses are the

> way to go.

> 

> So, I think that the "study" we are discussing is

> probably junk science.

> 

> Ciao, Carol

> 

> Carol S. Marcus, Ph.D., M.D.

> 

> 





=====

+++++++++++++++++++

""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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