Characteristics of radio-isotopes for intra-articular therapy.

Since Ansell, Crook, Mallard, and Bywaters (1963) and Makin and Robin (1964) initiated the method, the use of radioactive colloids in the treatment of chronic synovitis has become routine. The destruction of the inflammatory synovium, called synoviorthese or synoviolysis, is based on the irradiation of the serosa by colloidal particles, removed from the suspension injected into the articular cavity (Ballabio, Schiavetti, Caruso, and Merola, 1972; Bonneton, 1972; Webb, Lowe, and Bluestone, 1969). After injection, the radioactive colloid becomes distributed in the joint in the shape of the synovium, so that a scintigram shows a very similar distribution to that seen in an arthrogram (Fig. 1). The aim of the radiotherapist is to ensure that the energy of the ionizing radiation is absorbed in the synovium only. We must therefore consider the characteristics of the radio pharmaceuticals used for intra-articular therapy, and also the possibility of transfer of energy to tissues which must be preserved from irradiation (Ingrand, 1972; Roucayrol, 1972; Stevenson, Bedford, Hill, and Hill, 1971 b). The radiation emitted by the colloidal particles may irradiate not only the synovium but also the cartilage and bone marrow (Bonneton, 1972), depending on the range of emission of the radioisotope. Fortunately, autoradiographs show that the cartilaginous surface is usually free of radioactivity, which is concentrated in the synovium (Fig. 2). Consequently, the use of a colloid tends to result in localized irradiation, but there remains the possibility of leakage away from the joint via the lymphatic system. These problems have been the basis of a multi-disciplinary study at the Hopital Cochin (Delbarre, Cayla, Aignan, Roucayrol, Menkes, and Ingrand, 1968; Menkes, Aignan, Galmiche, and Le Go, 1972).