Pituitary ablation by yttrium-90 implantation: Some post mortem and clinical observations

Abstract

The pituitary gland was examined at autopsy from 21 patients who had had 90Y implantation, 20 with the aim of total pituitary ablation. By placing coronal histological sections on a millimetre-squared grid, areas of necrotic, damaged and normal pituitary tissue were measured and the volume and proportion of necrosis produced by a known radiation dose were calculated. A method for measuring the distance from the yttrium rod to a point of radiation damage was also developed, utilizing the same measuring grid and correcting for obliquity of yttrium rods in relation to the section by a mathematical method based on measurements of radiographs of the sphenoid bone with the pituitary in situ. An average of 90 per cent necrosis resulted from the 300 krad dose plan (range 70–100%). About 90% necrosis was required to effect a subnormal 48 h neck uptake of 131I. The mean threshold radiation dose for pituitary necrosis was 184 (range 85–346) krad. Similar thresholds were found for the cells in bone and for smooth muscle of the carotid artery; no structural defects had occurred in bone or artery.