Radioactive Selenium: a New Tracer for Detection of Cartilaginous Tumours

Abstract

Fixation of S35 is increased in cartilaginous tumors in comparison with other tissues and normal cartilage. The fact that S35 is a pure B emitter has induced the authors to use selenium with a half-life of 121 days, already used in the preparation of methionine[long dash]Se75 where it has replaced sulfur. Se75 follows the same metabolic route as sulfur, is a gamma emitter and is easily detected with normal scintillation equipment. When injected into rats intraperitoneally a very high excretion rate was noted, (45% within the 1st 24 hr.). In the series of cartilaginous tumors studied, all histologically proven, Se in the form of Na Se was injected intravenously. In patients with malignant cartilaginous tumors an increase of activity of the tumor areas was noted in relation to the contralateral area. Twenty-four hrs. following an injection, the background activity diminished considerably and the difference of activity between the tumor and the surrounding tissues was sufficiently raised to allow scanning of the area. In malignant tumors the relation between the activity over the tumor area and the symmetrical area is always above 1.5 and tends to increase to a factor of 2 or 3, whereas in benign tumors it is below 1.5 and remains level during the following days.