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
recombinant human thyroid-stimulating hormone (rhTSH) injection. 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 four parts:
(1) two extra doses of injections of rhTSH, (2) the administration of I-124, (3) PET imaging,
and (4) drawing blood samples.
Patients will receive two additional injections of rhTSH. 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.