HOW LONG RAI KILLS (updated repost)

[Guest guest]

Dear All,

While it is generally accepted that it takes a minimum of 5-6

months to kill off all cells that have taken up the RAI, there

are

some indications that cells may continue to die off for up to a

year

(or even a little longer).

Below are some quotations on the subject.

-

NYC

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RAI delivers most of its radiation to thyroid tissue in the first

2 weeks after therapy. At 4 weeks after therapy the RAI has

delivered well over 99% of its radiation dose. There can be a

delay of up to 6-12 months between delivery of the radiation and

cell death, especially with normal thyroid tissue.

A. , MD

Nuclear Medicine

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- from Dr. Ain, on why scans shouldn't be done sooner than 6

months apart ....

1). Radioiodine effects on killing thyroid cancer cells may take

a few

months to fully manifest. Although the I-131 is effectively gone

in a

few days, some of the tumor DNA damage caused by the ionizing

radiation does not result in the death of the cancer cell until

some

time later when it tries to divide and replicate.

2). For those tumor cells not killed by the radioiodine dose,

there is likely

to be some residual " stunning " by their exposure to sublethal

radiation,

causing inability to take up the next I-131 dose and resulting in

subsequent

radioiodine treatment failure, if attempted too soon after the

first treatment.

Recovery from this effect often takes several months.

3). Every I-131 treatment dose has some temporary adverse effect

upon the bone marrow cells. It takes several months for this to

be

minimized so that adverse effects do not accumulate and result in

otherwise avoidable toxicity.

For these reasons, and others, it is inadvisable to attempt I-131

therapies closer together than 5-6 months. For some patients, in

whom I have administered dosimetry-limited (maximal marrow

toleration) I-131 doses (300-900 mCi per dose) for severely

aggressive

disease, the interval between doses may be even greater.

Since I consider it ill-advised to prepare a patient for I-131

whole body scanning if the physician does not intend to treat

any detected disease, I do not do I-131 scanning at intervals

closer

together than those defined for therapy (as above). This approach

is based on the methodology utilized at the University of

Kentucky

Thyroid Oncology Service and may be different than approaches of

some other clinicians.

- B. Ain, M.D.

University of Kentucky Medical Center

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> .... I was told that the ablative RAI actively works

> to kill thyroid cells for a year.

Not quite true, the key word here is 'actively'. The RAI stays in

the thyroid

tissue for a period of time and 'actively' destroys it during

this time.

Think of it like a house fire. The rate of destruction starts

from zero at

the beginning and reaches a maximum at an hour or so (RAI, about

48h). After

this the fire gradually subsides but continues destruction for

another 24h

(RAI, about 1 week). After this, there are a few smouldering

heaps that go on

for another day or so (RAI, another week). After this, there is

the clear up.

Removing the rubble, (RAI, perhaps 2 or 3 weeks), then repairing

the damage

to the neighbours (Mr & Mrs Thyca live very close to their

neighbours). I

can't comment on the accuracy of the 1 year value, but the whole

thing does

take months to stabilise, while the 'active' period is only a

couple of weeks.

Ian Adam

Radiation Safety Officer

The Institute of Cancer Research

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" Iodine-131 dose In general, a dose of 75-100 mCi will ablate

residual thyroid tissue within 6 months following ingestion. In

some patients, it may take up to 1 year for complete ablation to

occur. "

http://www.cancernetwork.com/index.htm?News ---> click on

" cancers " , " head and neck " , then " thyroid cancer " , you'll see

an index of articles; click on " thyroid and parathyroid

cancers " .

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Betty's experience indicates thyca cells can sometimes continue

dying off for over a year ....

http://groups.yahoo.com/group/Thyca/message/18852

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