Radiosynovectomy in paediatric patients with haemophilic synovitis: can dosimetry tools optimise the administered activity and administration protocol?

Radiosynovectomy is a well-established radionuclide therapy that is commonly indicated for the treatment of joint pain arising from arthropathies such as rheumatoid arthritis by intra-articular injection of beta emitting colloidal preparation. Great Ormond Street Hospital has an existing radiosynovectomy service to treat paediatric patients for an uncommon application in the UK – patients with haemophilic synovitis and inhibitory antibodies (FVIII or FIX) to prophylactic clotting factors. Benefits of the treatment include: reduced number of bleeds into the affected joint, reduced pain and improved range of motion. A risk associated with the therapy is migration of the radiopharmaceutical to the liver, spleen, lymph nodes and bone marrow. The recommended radionuclide, volume and administered activity in the radiosynovectomy procedural guidelines are intended for adult joint sizes (Clunie et al., 2003). For diagnostic nuclear medicine, the activity administered to paediatric patients is scaled according to body mass, which is unlikely to be an appropriate measure for radiosynovectomy. There is some evidence in the literature that activity is scaled to 50-100% of the adult recommended activity levels, which is the current practice at Great Ormond Street Hospital. However, it is desirable to optimise the administered activity levels within the bounds of 50-100%.

The aims of the research project are as follows:

• To assess the biodistribution and resulting absorbed dose (Gy) to the synovium and growth plate using post-procedural SPECT-CT imaging and dosimetry methods.
• Investigate whether dosimetry tools can optimise the selected radionuclide, the radionuclide concentration and administered activity on an individual patient basis to deliver the maximum absorbed dose to the synovium and minimum absorbed dose to the growth plate.
• To assess the absorbed dose (Gy) to affected organs such as the liver, spleen, lymph nodes and bone marrow in the event of migration of the radiopharmaceutical from the joint capsule.
• To consider the aforementioned aims in the clinical context such concurrent treatment regimes, and also the practical aspects associated with the therapy such as unintended joint motion resulting in radiopharmaceutical migration.