Very confused 5 days before scan

[Guest guest]

Mara,

Feeling confused at this time is very normal because thyca follow-up

monitoring can be complicated & when we are hypothyroid in preparation

for a RAI scan/treatment, every thing about body functioning slows

down - including thinking & memory. This is probably also why your

memory about last years scan is a bit fuzzy.

For now, the priority is to make sure that your scan & possible

treatment dose are done properly. Once you are back on your thyroid

hormone replacement pills and feeling stronger, the you can review

your follow-up monitoring needs and options with your doctor.

Getting Ready for Scanning

~~~~~~~~~~~~~~~~~~~~~~~~~~

Are you following the low iodine diet? It is a good idea to keep

up with the diet until after you get a clear scan. If your scan

is not clear & you need a bigger treatment dose of RAI, stay

on the LID until 48 hours after you've received the treatment

dose. (This time frame is from the LID protocol at St. 's

Hospital Toronto - other hospitals/physicians may have different

guidelines & it would be best to discuss this with your doctor if

he is going to administer a treatment dose).

The blood test you had on Friday is still important, because your

TSH must be elevated to above 30 for the tracer dose of radioactive

iodine to be absorbed by any remaining thyroid tissue or thyca

cells. If your doctor doesn't confirm your TSH level, you can

ask.

For women, if there is any chance of pregnancy, usually a pregnancy

test is given prior to administering the RAI tracer dose. There

seems to be some variation in what dose is used for scanning, but

it is usually under 10 mCi and list members have mentioned doses

of 3- 5 mCi. The RAI is given in either pill form or in liquid. The

liquid is apparently tasteless and in a bit of water. (I've had

the pill so I can't speak from exerience here).

You can confirm when your whole body scan will be done after you take

your tracer dose. The whole body scan should be done at 48 hours

after taking the tracer dose. (Dr. Ain/July 13/00)

If your scan shows that there is indeed some remaining thryoid tissue

or thyca cells, then your doctor will want to give you a treatment

dose of RAI - usually 100 mCi or higher. It seems important to

get the treatment dose within 72 hours of receiving your scanning

dose in order to avoid stunning. The stunning of the thyroid cells

could minimize the benefits ot the treatment. Our list doctors may have

some comments, and I've copied part of a study about stunning after

5 mCi scanning dose below.

It may be wise to make some plans just in case you do need the

treatment dose. There's a good description of RAI treatment &

self-help suggestions at the thyca site: http://www.thyca.org

under radioactive iodine.

After You Are Back on Meds

~~~~~~~~~~~~~~~~~~~~~~~~~~

Once you are finished with all the scanning adventures, have

been back on your meds & are feeling better, THEN you can review your

needs and options for ongoing follow-up. Try not to worry about this

issue until a few weeks from now.

What does your doctor suggest & why?

-still monitoring your TG & antibodies for changes?

-neck ultrasounds?

-scans that do not rely upon iodide uptake (eg Thallium, Sestamibi,

18-FDG-PET etc.?)

There will be time to straighten out your long-term monitoring when

you feel stronger.

Good luck with your scan on Wednesday & share any remaining questions

or concerns you may have.

.

dx Pap-Hurthle cell variant, tt 9/99, RAI 12/99

.................

J Nucl Med 2000 Jul;41(7):119

Absence of thyroid stunning after diagnostic whole-body

Scanning with 185 MBq 131I.

Cholewinski SP, Yoo KS, Klieger PS, O'Mara RE. Department of Radiology,

University of Rochester Medical Center, New York, USA.

There has been recent controversy regarding the optimal protocol for

imaging and ablation of post-thyroidectomy patients. Several authors

have suggested that a scanning dose of 185-370 MBq (5-10 mCi)

(131)I may be capable of producing a stunning effect on thyroid tissue

that may interfere with the uptake and efficacy of the subsequent

ablation dose of radioiodine. The purpose of this study was

to determine whether a 185-MBq (5 mCi) diagnostic dose of (131)I

produces a visually apparent stunning effect 72 h before (131)I

ablation therapy. RESULTS: No cases of visually apparent thyroid

stunning were observed on any of the postablation scans with regard

to the number of (131)I foci identified or the relative intensity of

(131)I uptake seen.

CONCLUSION: Diagnostic whole-body scanning can be performed effectively

with a 185-MBq (5 mCi) dose of (131)I 72 h before radioiodine ablation

without concern for thyroid stunning.