Quantitative External Counting Techniques Enabling Improved Diagnostic and Therapeutic Decisions in Patients with Well-Differentiated Thyroid Cancer

Abstract

A quantitative technique is described which allows the physician to predict more accurately whether a recurrent or metastatic well differentiated thyroid carcinoma is amenable to 131I therapy or is better treated by other means. A calibrated uptake probe and scaler system is used to obtain conjugate view (i.e., diametrically opposed) counting rates for the whole body and any areas of abnormal uptake (lesion) at 24, 48 and 72 h following administration of 2 mCi 131I. Quantitative calculations accounting for patient attenuation, lesion size and geometrical factors provide a determination of lesion uptake as well as the effective half-life of 131I in the lesion. The radiation dose which would be delivered to the lesion by a given therapeutic amount of 131I may be calculated to help determine the desirability of 131I treatment. The results of patient studies indicate the potential benefit of such quantitative evaluation.