RAI LIFETIME LIMIT (updated repost)

[Guest guest]

While there are almost as many opinions as there are thyroidologists, the going

opinion seems to be that there is no real " life time limit " of RAI treatment

dosing, or if there is, it's much, MUCH higher

than many doctors seem to believe.

The bottom line, though, is that we must always balance the risks against the

potential gains. Personally, I'd rather treat my known cancer now, as

efficiently as possible, and worry about any future

cancers or health problems if and when they may occur.

-

(not a doctor)

NYC

TT 2/99 dx pap/foll; RAI 100 mCi 3/99 & 4/00; clean scan 3/02;

current TSH ~.06 on .225 levothyroxine

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Unfortunately, I've seen too many references to the fictitious

" lifetime limit " of I-131. There is absolutely no basis in reality for

such a limit. Although you may find references to such a limit in some

medical articles, careful research of this claim reveals that there is no

data anywhere to support such a concept. This is another " old wives tale "

of endocrinology.

In fact, I have treated patients to total cumulative doses of 2000

to 3000 mCi without any significant ill effect from the treatment, aside

from dysfunctional salivary glands. If the thyroid cancer is distantly

spread and still is able to respond to radioiodine, then there is no reason

to withhold therapy if it can be helpful. As long as each single I-131

dose is within the safety margins of 200 REM marrow exposure and less than

80 mCi I-131 retained in the lung at 48 hrs (this may permit single doses

up to 650 mCi in some patients), there should be no permanent ill

consequences from necessary thyroid cancer treatment. The biggest problem

is the use of repetitive low dose (< 200 mCi) treatments for aggressive

distant disease. This may result in the use of many doses, with each

particular dose too low to destroy the thyroid cancer cells.

[...and ...]

>I would like to know what your endos and nuclear med docs

> tell you the limit of RAI is. I have had 8 tx in 6 years, for a total

> of 1400 milicuries. My scans are still positive but Mayo says no

> further tx unless further mets.

As I have previously posted, there is no true or definite lifetime

cumulative radioiodine treatment limit, provided that appropriate

parameters are maintained for each dose, therapeutic response and

situation warrants treatment, and bone marrow effects are closely

monitored.

On the other hand, the question, above, brings up a different

issue. Thyroid cancer metastases to bone are notoriously resistant

to almost any dose of I-131. Although the reasons for this are not

totally known, a reasonable clinical approach to treat this problem

is known. Such metastases to bone must be surgically excised, often

requiring extensive neurosurgery or orthopedic surgery with

implantation of metal supports. This should be followed by high-dose

I-131 therapy, utilizing a dosimetry approach to dose selection and

monitoring.

This approach can be uniquely successful, even in the face of otherwise

recalcitrant disease, but it requires coordination and cooperation

between the surgeon and the endocrinologist.

**************PLEASE BE ADVISED**********************

THE INFORMATION CONTAINED IN THIS COMMUNICATION IS INTENDED

FOR EDUCATIONAL PURPOSES ONLY. IT IS NOT INTENDED, NOR SHOULD

IT BE CONSTRUED, AS SPECIFIC MEDICAL ADVICE OR DIRECTIONS. ANY

PERSON VIEWING THIS INFORMATION IS ADVISED TO CONSULT THEIR OWN

PHYSICIAN(S) ABOUT ANY MATTER REGARDING THEIR MEDICAL CARE.

*************************************************

B. Ain, M.D.

Associate Professor of Internal Medicine

Director, Thyroid Nodule & Oncology Clinical Service

Director, Thyroid Cancer Research Laboratory

Division of Endocrinology and Molecular Medicine

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> I had heard there was a limit to how much RAI one could have

> in a lifetime? Does anyone else know about this?

Many thyroidologists feel that there is maximum dose of RAI that

may be administered to a patient, but that Maximal Safe Dose

varies from center to center.

There are other thyroidologists who feel that in patients with

aggressive Thycas, one can use larger and larger doses of RAI,

without worrying about the maximal dose administered.

- Arturo R. Rolla, MD

Boston, MA

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Tuttle, MD, an endocrinologist at Memorial Sloan

Kettering in NYC, spoke recently at the ThyCa conference,

and said that leukemia cases CAN show up 40-50 years later,

although he has seen it once out of 15,000 cases with RAI up

to 1000 mCi.

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