Applications of Low Level Counting to Studies of Calcium and Strontium Metabolism in Human Subjects

Abstract

Low level whole body and sample counting systems have been used in simultaneous studies of the turnover of ⁴⁷Ca and ⁸⁵Sr in ten patients undergoing radiotherapy for cancer at various sites not involving bone. The whole body counter used in the double tracer studies consisted of four 11 cm diameter × 5 cm thick Nal (Tl) crystals set up at the Radiological Protection Service in a lead-lined room excavated in chalk, which has a low natural radioactive content; ancillary studies were made in a demountable clinical low background room, at the Royal Marsden Hospital, shielded by 15 tons of chalk contained in about 700 polythene lined three-ply paper bags. Excreta samples were measured on a low background 7·5 cm diameter × 7·5 cm thick Nal (Tl) crystal. 100 channel pulse height analysers were used to record spectral data. Activities administered ranged from 0·3 to 2·4 μc, the most convenient combination being 0·3 to 0·5 μc of each nuclide. Whole body measurements, and the collection of excreta were carried out for about ten days with each patient. Methods of analysing the data are described and estimates of percentage retention R, at various times t, based on body counting and excreta measurements, are compared. Limitations imposed by naturally occurring radioactivity and by contamination are discussed. Retention data from this small, highly selected group, are presented as the power function R_t = At⁻ⁿ; values of n, based on body counting, ranged from 0·08 ± 0·033 to 0·39 ± 0·047 for ⁴⁷Ca and 0·20 ± 0·026 to 0·66 ± 0·052 for ⁸⁵Sr, the higher values being found for patients having carcinoma of the breast. Values derived from excreta assay, whilst in general somewhat lower, showed the same trend.