Dosimetry in Radiosynoviorthesis

Although there are several radionuclides suitable for radiosynoviorthesis (RSO), not all of them can irradiate deeper synovium. Yttrium-90 (Y-90) is the beta radionuclide with more penetration range; therefore, it is predominantly used to treat knees. The aim of this paper is to highlight several dosimetry concepts to compare Y-90 and Sm-153, also discussing the feasibility of implementing a dose planning methodology for both in RSO. The MCNPX Monte Carlo nuclear code version 2.6 was used for calculating S-values from which the activity to be injected into the joint was obtained. This activity is considered sufficient to deliver a 100-Gy absorbed dose in 1 mm of synovial tissue. The simulated mathematical model consisted of a system formed by several cylindrical slabs of 1-mm thickness, aligned consecutively. The different areas of the cylinder base simulate several synovial membrane sizes. The effective treatment range for each radionuclide was also calculated. Quantification of the synovial joint features (synovial thickness and synovial surface) by diagnostic imaging, such as magnetic resonance (MRI) combined with a Monte Carlo simulation, can be used to achieve a treatment planning strategy in RSO with the available radionuclides.