Radiosynovectomy (radiosynoviorthesis)

Indications

• Licensed (SPC core data): ⁹⁰Y, synovial hypertrophy of the knee in chronic inflammatory arthritis (especially RA) and haemophilic arthropathy; ¹⁸⁶Re, mono- or oligoarthritis of medium joints, including RA, haemophilic arthropathy and chondrocalcinosis; ¹⁶⁹Er, small joints of the hands and feet after failed or contraindicated steroid injection
• Rheumatoid arthritis and seronegative spondyloarthropathy (reactive and psoriatic arthritis, ankylosing spondylitis) with persistent synovitis after ≥1 failed intra-articular steroid injection; best results with little joint damage (Steinbrocker I–II)
• Haemophilic synovitis: chronic synovitis (>3–6 months) or recurrent bleeds into a target joint despite factor replacement. WFH 2020 recommends radioisotope synovectomy as first-line non-surgical synovectomy
• Diffuse pigmented villonodular synovitis (tenosynovial giant cell tumour): adjuvant after surgical synovectomy to prevent relapse (approved indication in Germany)
• Off-label in selected patients with documented consent: osteoarthritis with secondary synovitis resistant to other treatment; recurrent effusion after synovectomy; recurrent effusion after arthroplasty once loosening and infection are excluded

Contraindications

• Absolute: pregnancy; breastfeeding; local skin infection or septic arthritis; ruptured popliteal (Baker's) cyst; recent joint surgery or arthroplasty with fresh scars (<6 weeks); uncontrolled bleeding including massive haemarthrosis (except haemophilia with factor cover)
• Relative: extensive joint instability with bone destruction; high-grade bone destruction (poorer response; possible subchondral osteonecrosis in end-stage osteoarthritis)
• Relative: children and young people <20 years. Restrict use, except haemophilia, where benefit usually outweighs risk
• Radiocolloids are not approved for the same indications in every country: follow national marketing authorisations (EANM 2021)

• Physical data (EANM Table 1): ⁹⁰Y T½ 64.1 h, E_max 2.26 MeV, mean tissue range 3.6 mm, pure β. ¹⁸⁶Re T½ 89.25 h, 0.98 MeV, 1.2 mm, with 7.5% 137 keV γ. ¹⁶⁹Er T½ 225.4 h, 0.34 MeV, 0.3 mm.
• Activities are empiric and largely standardised. A physicist's calculation is not routinely needed unless standard activities are changed, but national rules on individual dose planning apply.
• Children: no general activity recommendation. Published series used half the adult activity for children or for body weight <20 kg. ¹⁶⁹Er is not approved for children in Germany.
• Minimum interval between treatments of the same joint is 6 months (EANM, WFH). Observe the licensed annual cumulative activity.
• WFH 2020 accepts ³²P, ⁹⁰Y, ¹⁸⁶Re or ¹⁸⁸Re for haemophilia. It advises one dose of clotting factor per isotope injection, steroid co-injection where possible and ≥24 h immobilisation. EANM advises intensified factor cover for ≥3 months.
• Approvals (EANM Table 2): all three agents in Germany, France, Switzerland, Spain, Turkey and the Czech Republic; ⁹⁰Y only in Belgium, the Netherlands, Luxembourg, Portugal, Norway and Ireland.
• United States: Drugs@FDA lists no ⁹⁰Y, ¹⁸⁶Re or ¹⁶⁹Er radiocolloid, so there is no FDA-approved agent for this use. The one FDA-approved colloid, ³²P chromic phosphate (Phosphocol), is listed as discontinued. Its label covered malignant effusions, stated it was not indicated for intra-articular treatment of haemarthroses, and warned of leukaemia in two children after intra-articular use.

• Radiation synovitis: more pain, swelling or effusion 6–48 h after injection, more common with ⁹⁰Y. It is self-limiting: cool the joint and add an NSAID if needed. Steroid co-injection lowers the risk.
• Joint infection is a procedural risk (about 1 in 3000 to 1 in 100 000 intra-articular injections), and was the commonest serious adverse event reported. Aspirate and culture at once; lavage or arthroscopy if antibiotics fail within 24–48 h.
• Skin and needle-track radiation injury from leakage on withdrawal: discoloration, blisters, ulcer or scar, appearing 3–4 weeks to 8 months later. Prevent it by flushing the needle and compressing the site.
• Para-articular injection or leakage can cause soft-tissue radionecrosis, the most severe local complication. ⁹⁰Y is the most potent (full-thickness necrosis possible); ¹⁸⁶Re burns usually heal in 3–4 weeks; ¹⁶⁹Er burns need only conservative care. There is no agreed management: decide with the surgeon, with radiation protection for the surgical team.
• Leakage with strict immobilisation: ⁹⁰Y knee about 1.8–1.9% (mean effective dose about 37 mSv for 200 MBq, mostly to lymph nodes); ¹⁸⁶Re 2.5–3.9%; ¹⁶⁹Er about 0.1%. Leakage ≥5% raises chromosomal aberrations; a semi-rigid splint doubled lymph-node uptake.
• Thromboembolism is linked to immobilisation, not the radiocolloid. Pulmonary embolism has been reported.
• Possible avascular necrosis of exposed subchondral bone in end-stage osteoarthritis, which may complicate later arthroplasty. Avoid treating joints with established bony damage.
• No proven increase in cancer after radiocolloids. Two leukaemias were reported in children after ³²P, but causation was not established.
• Haemophilia: bleeding from the puncture is low with adequate factor cover, but the bleeding tendency stays raised for up to 3 months.

• Follow national legislation for handling authorisation, approved treatment rooms (including off-site rooms such as theatres), contamination monitoring, storage and waste (EANM 2021).
• Staff: β-emitters give a high skin dose, so monitor H_p(0.07) with ring dosimeters. Use acrylic syringe shields (about 1 cm for ⁹⁰Y), forceps or tweezers, a shielded box for prepared syringes, and standard fluoroscopy protection with hands out of the beam.
• Waste: separate by nuclide, because clearance times differ with half-life (64 h, 89 h, 225 h).
• Patients: excretion is mainly urinary in the first 2 days. Advise flushing twice, careful hand hygiene and separate washing of heavily soiled clothing. Catheterise incontinent patients for 3–4 days, and staff wear gloves when emptying bags.
• Pregnancy is an absolute contraindication and should be avoided for ≥4 months after treatment (SPC). Stop breastfeeding before RSO: ⁹⁰Y transfer into breast milk has been shown, and ¹⁸⁶Re and ¹⁶⁹Er are handled the same way.
• Written discharge information is mandatory (EANM 2021); any release or contact restrictions follow local rules.