90Y ferric hydroxide colloid.

At the Radiochemical Centre we have recently developed a new 90Y colloid which has greater stability than the currently available 90Y silicate colloid and appears from the results of animal tests to be suitable for the treatment of rheumatoid knee joint effusions. In this report the need for a new 90Y colloid is assessed and the preparation and properties of the new colloid are described. Currently two radioactive colloids are routinely available from the Radiochemical Centre for therapeutic applications: 90Y silicate and 198Au colloid. Both have been shown to display considerable leakage from the synovial cavity of patients undergoing treatment for rheumatoid knee effusions. '98Au has the additional disadvantages of being a y-emitter and of giving relatively low energy ,B particles with a maximum range in tissue ofonly 4mm.,comparedto a range of 11 mm. forthe more energetic/I particles from 90Y. An alternative colloid in which 90Y was adsorbed on particles of ion exchange resin was produced until last year, and was considered to be a more useful agent for knee joint treatment. Unfortunately we were forced to discontinue its supply because of technical difficulties encountered in maintaining preparation of the colloid to a uniform standard. More recently the supply of chromic phosphate (32p) colloid was discontinued because 90Y was felt to be a more suitable radionuclide for therapeutic work. It was decided to develop an improved 90Y colloid of relatively large particle size, which could replace the existing 90Y silicate product in its applications and, at the same time, be suitable for intraarticular injection. To achieve a product of high stability and with the desired physiological properties, we decided to investigate the use of very high specific activity 90Y, derived from P decay of strontium 90 (9Sr), rather than the usual low specific activity 90Y produced by reactor irradiation of 89Y. In the new process the high specific activity 90Y is separated by an ion exchange technique. The 90Y is then converted to its chloride, S. C PEAKE