IODINE CONTRAST & RAI SCAN (Dr. Ain REPOSTS)

[Guest guest]

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Combined from several of Dr. Ain's letters:

My clinical practice consists exclusively of thyroid cancer

patients, many referred because of difficult metastatic disease. I

frequently do CT scans of the lungs since they have the highest sensitivity

for gross metastases in that region. I NEVER use any iodinated contrast

material since such contrast will not provide any benefit for such a study

and interferes with I-131 studies and treatments. The lung tissue is

mostly air spaces and the interface between solid cellular metastases and

air is sufficient to provide the full informative value of the study. If

there is any need to visualize solid structures in the mediastinum,

abdomen, neck, or brain, then gadolinium-enhanced MRI scans provide

sufficient detailed information without compromising the use of I-131.

Additional modalities useful for the neck region include sensitive

ultrasound with skilled operators (very user dependent).

Unfortunately, some physicians use identical approaches in

evaluating thyroid cancer as they do for other unrelated malignancies.

Such an approach is unsatifactory for thyroid cancer, which requires unique

knowledge and clinical management techniques.

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There is NO effective strategy which can prevent iodinated contrast

from interfering with radioiodine uptake. Once this contamination

occurs, the only useful thing to do is wait until the urinary iodide

test show that this non-radioactive iodine has passed. There is no

way to " feed " iodine to thyroid (or thyroid cancer) cells to prevent

this problem. In fact, such efforts are more likely to make the

situation worse.

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Stable (non-radioactive) iodine contamination from iodinated contrast dye

is certainly an important potential contribution to I-131 scan & /or treatment

failure. If one has been exposed during the course of a CAT scan or other

radiographic procedure, it is possible that it may take nearly a year to clear

the stable iodine; however, the length of time may vary from a couple months

to more than 10 months. To determine when this iodine has cleared requires the

following:

1). Start a low iodine diet (carefully followed) for one week. Maintain the

usual

thyroid hormone medication

(Note: this is not a preparation for scan or therapy).

2). On the last day of the diet, collect an accurate and full 24-hour urine

sample.

3). Have the urine sent for a total urine iodide analysis. The only commercial

lab

that I have found to be reliable is at the Mayo Clinic (Rochester, MN).

4). A total urine iodide of 80 (or less) micrograms in 24 hours demonstrates

that

the stable iodine interference has sufficiently passed.

5) If the urine iodide is much higher, it may be useful to wait 1-2 months and

repeat sequence 1) through 4) to evaluate the body's stable iodine content.

This sequence is repeated until the urine value is sufficiently low. A urine

iodide

value sufficiently low demonstrates that the full scan/therapy preparation may

be

initiated without interference from the previous contrast dye administration.

This is the general method that I advise physicians to follow in answering when

their patient may be optimally cleared of such stable iodine contamination.

On the other hand, sometimes clinical situations arise in which it is not

possible

to wait until every parameter is optimal.

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The correct ordering information to obtain a urinary free iodide from

Mayo Clinic Laboratories is:

Mayo Medical Laboratory

Call for Mailing and Processing Information:

Test Number 9549

Iodine, Urinary Free

Specimen required: 10 mL from a 24-hour urine collection.

Send specimen in a plastic 13 mL urine tube.

Keep refrigerated (keep specimen cool with frozen coolant April-October,

refrigerated coolant November-March)

NOTE: 24-HOUR VOLUME IS REQUIRED ON REQUEST FORM FOR PROCESSING.

CPT Code: 82190

Although there may be other reputable laboratories to do this particular

analysis,

the only commercial lab where I have obtained reliable results is at this

particular one.

Most hospital laboratories can send the urine sample directly to this site if

instructed.

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The issue of stable iodine contamination from CT scan contrast is

important, but just one of many factors to consider in order to

optimize radioiodine effectiveness. Sometimes, it is necessary to go

ahead with I-131 even if conditions are not perfect, knowing for

later on that better preparation techniques will be followed. ALWAYS

maintain a sense of PROPORTION. Frequently, being presented with a

patient after their thyroid surgery who had been exposed to CT

contrast dye just before the surgery, I proceed with the I-131 scan &

treatment. For follow-up, there may be a higher need for repeat

therapy, but this is not always the case.

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

Department of Internal Medicine, Room MN524

University of Kentucky Medical Center

800 Rose Street, Lexington, Kentucky 40536-0298

trejolie10@... wrote:

> Hi all, hi

> if you can find it I need DR AINS INFORMATION ABOUT IODINE CONTRASTS AND rai?

> MANY THANX /

> jOLIE/CA