Personalized Treatment Planning for Radio-iodine Therapy of Thyroid Disease

Radioiodine treatment for thyroid disorders represented an early example of individualized medicine. Since its introduction 80 years ago, the therapeutic I-131 dosage has usually been tailored to individual patient requirements based on the uptake of a tracer radioiodine dose. Various techniques have been employed to estimate the administered dose of I-131 for optimal therapeutic benefit. Estimated exposure has typically been extrapolated from the results of activity measurements at one or two time points, e.g., at 4 and 24 hours. We now know that treatment of hyperthyroid Graves' disease with these methods lead to a 13-25% rate of failure to cure hyperthyroidism and a 46-80% rate of long-term hypothyroidism in cured patients. Similarly, such relatively crude dosimetry doubtless result in significant overtreatment in the case of remnant ablation for differentiated thyroid cancer.

For patients with differentiated thyroid cancer requiring remnant ablation, the administered activity has, in most cases, been derived empirically, ranging between 30-100 mci. The high success rates in ablating remnant thyroid tissue implies that many patients are still treated with higher 131-I doses than required, with potential side effects, such as radiation sialadenitis.

Pilot Study Rationale; Our overall objective is to provide the optimal dose to each patient. This study will apply a novel "wearable" radiation detection technology to determine continuous cervical measurements over days following tracer radioiodine administration will provide information that permits the tailoring of subsequent therapeutic radioiodine doses more precisely to improve clinical outcomes, as described above.

The actual therapeutic dose decisions in this pilot trial, however, will not be based on the collar device measurements. Patients with Graves' disease will receive 180-200 µCi I-131 per gram of estimated gland mass based on the conventional method of dose calculation, based on a 24-hour % uptake and gland volume. Most patients with thyroid cancer would receive the 30 mCi dose for remnant ablation prior to the placement of the COTI device, as per the American Thyroid Association (ATA) guidelines.

STUDY DESIGN AND METHODS This will be an unmasked prospective pilot study involving patients with Graves' disease (Group I) and differentiated thyroid cancer (Group II). Five patients in each group will have radiation activity measurements using the COTI devise. All persons in the study will receive 131-I treatment based on the current standards of care for dose estimation.