Uptake of colloidal radioactive yttrium by synovial membrane.

Surgical synovectomy is sometimes useful in the management of patients with rheumatoid arthritis. Ansell, Crook, Mallard, and Bywaters (1963) reported some encouraging results using radioactive colloidal gold, 198Au, given into the knee joints of patients with persistent effusions in rheumatoid arthritis and allied conditions, with the aim of producing a radiation synovectomy or ablation. Any small particle present in synovial fluid within a joint is taken up by the synovial membrane, because amongst the secretory cells making up the membrane there is a population of phagocytic cells. These cells were shown to take up the colloidal particles of radioactive gold and to retain them for at least 24 hours. 198Au has a maximum beta-particle energy of 0 96 MeV and a range of 4 mm., although the average penetration is only about 1 mm. The inflamed synovial membrane of the knee joint in rheumatoid arthritis varies greatly in thickness, but often exceeds 1 cm. Although it was realized that 19"8Au was not able to deliver an effective radiation dose to the full thickness of the inflamed membrane, it was hoped to achieve some useful effect by irradiating to an average depth of 1 mm. Ansell and others (1963) suggested that 90Y might be preferable to 198Au because of its more energetic beta emission. 90Y has a maximum beta-particle energy of 2-25 MeV, and a maximum range of 11 mm. The average penetration is about 4 mm. It has a half-life of 2'67 days, similar to that of 198Au, 2*70 days. The short half-life is an advantage in radio-therapeutic applications where there is any danger of the isotope diffusing from the site of administration over a long period. The surface density of 198Au needed to give a dose of 10,000 rads at a depth of 1 mm. is 145 ,lc. per sq. cm. The corresponding density for 90Y is 37 juc. per sq. cm. The doses at 2 mm. depth for these densities of the two isotopes are 100 rads and 3,000 rads respectively. A further advantage of the pure beta-emitter, 90Y, over 198Au, which has a 0-41 MeV gamma-ray, is the absence of any appreciable gamma dose to distant organs, such as the gonads. In view of these indications of 90Y as a more suitable therapeutic agent than 198Au, we undertook a study of the behaviour of the resin colloid of 90Y injected into the knee joint of the rabbit.