TARGETED RADIOTHERAPY WITH SM-153-EDTMP IN 9 CASES OF CANINE PRIMARY BONE-TUMORS

Nine dogs with primary bone rumours were treated with Samarium-153-EDT MP (Sm-153-EDTMP). Conventional treatment protocols were precluded by the size of the dogs and the owners' refusal of limb amputation. All t he rumours were of the appendicular skeleton; 4 were confirmed osteosa rcomas. The other 5 tumours were radiologically suspect for osteosarco ma. Bone scans were performed on all dogs using Technetium-99m-methyle ne diphosphonate (Tc-99m-MDP) before administration of Sm-153-EDTMP. R egions of interest were identified over the contralateral limb at the same site as the tumour and counts per pixel were recorded for Me tumo ur and contralateral limb and expressed as a ratio. The dogs were give n 1 injection of 37 MBq/kg (1 mCi/kg) of Sm-153-EDTMP intravenously. T horacic and primary tumour site radiographs were taken at monthly or 2 -monthly intervals to monitor progression of the primary tumour and se arch for evidence of metastasis. Two dogs showed no response to treatm ent, with an increase in bone pain, and were euthanased within 1 month . In 1 dog, a tumour of the scapula underwent complete involution and the dog is considered free of disease at 20 months post Sm-153-EDTMP t reatment. The overall tumourcidal effect of a single dose of Sm-153-ED TMP on primary bone tumours was difficult to evaluate in this group of dogs, as, with one exception, all the primary tumours progressed over time and the dogs were euthanased. Pain control, for which Sm-155-EDT MP is used in man, was not evident, except in the dog that responded c ompletely to treatment.