Absorbed dose due to beta-rays from radioactive colloids in radiation synovectomy

Assuming that colloidal particles of 198 Au or 90 Y are adsorbed by the synovial surface so that they form a very thin plane source of activity, the dependence of the absorbed dose on the distance from the source is calculated according to Berger's method and the methods of Loevinger et al. and Cross. Considering an infinitely thin plane source, a model often used in the literature, excellent agreement among the three methods is obtained at distances above 0.05 mm, A plane source having a thickness of 20-30 μm appears to be a more reasonable model, approximating more closely to the actual distribution of colloidal particles in the synovial membrane. These two approaches are compared and shown t o give the same dose at distances greater than 0.1 mm.