Comparison of I-124 and I-131 Radiopharmacokinetics in DTC Patients With Thyroid Hormone Withdrawal

This research study is to compare the radiopharmacokinetics of I-124 to the radiopharmacokinetics of I-131 in patients who have well-differentiated thyroid cancer after thyroid hormone withdrawal. I-131 is routinely used for imaging and dosimetry for patients with well-differentiated thyroid cancer. In this study, I-124 is administered orally in capsular form, and the radiopharmacokinetics of I-124 is compared with I-131. I-124 is another isotope of iodine, which is cyclotron-produced. I-124 has multiple advantages: * Ideal Half-Life (4.2 days) for delayed imaging. * High resolution tomographic imaging. * Feasibility of quantitating lesion uptake. * Potential of dosimetry for the planning of radioiodine therapy. Voluntary patients will have I-124 dosimetry performed in addition to the I-131 dosimetry, which is planned as part of routine clinical care. I-124 dosimetry is composed of three parts: (1) the administration of I-124, (2) imaging, and (3) drawing blood samples. Patients will start 3-5 weeks of thyroid hormone withdrawal. This is similar to the procedure for I-131 dosimetry. Second, they will receive I-124. I-124 is similar to I-131 except I-124 decays in a different way to emit a positron so that the PET scanner can be used for imaging. I-124 is given in the form of one or several capsules, which are taken by mouth. This is also similar to I-131. Third, PET/CT imaging is done for approximately 30 minutes to one hour on five consecutive days. Radiation from PET/CT scan is far less than what they receive from a diagnostic CT scan. For the fourth part, a technologist will draw about 5 cc from the forearm on each of the five consecutive days. This is also similar to I-131. Initially, all patients will be randomized to one of two study groups. The first group will have the I-131 dosimetry performed first followed by the I-124 dosimetry, and the second group will have the I-124 dosimetry performed first followed by the I-131 dosimetry. The risk of this study is considered very low, and the potential benefits to the patient are considered very high.

Sex

All

Minimum age

18 Years

Inclusion Criteria:

* 18 years or older,
* Well-differentiated thyroid carcinoma,
* Referred for 131-I dosimetry,
* Suspected of having metastases, which includes but is not limited to elevated TG without antibodies, clinical mass suggestive of metastases, radiographic finding on CT, MR, PET, and/or ultrasound, etc. suggestive of metastases, etc., and
* Preparation for dosimetry and treatment planned with thyroid hormone withdrawal.

Exclusion Criteria:

* \< 18 years of age,
* Pregnancy or breast feeding,
* Inability to comply with instructions,
* In ability to tolerate hypothyroidism as determined by the opinion of the referring endocrinologist,
* Simultaneous participation or participation in any other research study within the last month,
* A body weight greater than 350 lbs., and/or
* A creatinine \> 1.5 mg/ml for males and 1.4 mg/ml for females.