and intracavitary treatments

Table 7.1), and the usual activity per knee joint is 185 MBq. Rhenium-186 (¹⁸⁶Re) and erbium-169 (¹⁶⁹Er) are mentioned for completeness, as they are used outside the UK and discussed in the literature. The rationale for using each radionuclide in different sized joints may be seen by looking at the average penetration of the beta particles in tissue; 3.6 mm for ⁹⁰Y in large joints, 1.1 mm for ¹⁸⁶Re in medium joints and 0.3 mm for ¹⁶⁹Er in small joints. The high energy beta particles emitted by ⁹⁰Y result in the production of bremsstralung radiation (see Chapter 2), which can be detected externally.