The value of 75Se-selenomethionine scanning in solitary nodules of the thyroid gland.

Abstract

This paper describes the use of 75Se-selenomethionine in the study of thyroid nodules. Making use of the different main gamma energies of 75Se and 125I and the short physical half-life of 99Tcm, sequential comparison scanning was carried out in a series of 48 patients with solitary thyroid nodules in which histology was established. Preliminary phantom studies and measurements on a biopsy specimen established that the threshold of detectability of a tumour was 1·5 cm diameter for 75Se and 0·5 cm for 125I. The absorbed dose for the activities used was estimated to be 4·5 rads to the liver and 1·05 rad to the gonads from 150 μCi of 75Se and 30–105 rads to the thyroid gland from 75 μCi of 125I. Eight out of 11 malignant conditions gave positive 75Se-selenomethonine scans. There were only four positive scans in 32 benign conditions and three of these were attributable to physiological or pathological change. The value of the complementary scans was shown in solitary nodules. Diffuse uptake of 75Se-selenomethionine indicated a generalized change in the thyroid. There was no established relationship between the pathology and the intensity of the 75Se uptake. In one case of follicular carcinoma the 45-minute uptake of 75Se was estimated to be 4·8 per cent of the dose above background. The operation specimen contained 18 μCi 125I and 4·6 μCi 75Se per 100 g corrected to scan dates.