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Radiopharmaceuticals for Radiation Synovectomy: Evaluation of Two Yttrium-90 Particulate Agents

Department of Radiology, Department of Nuclear Medicine, University of Massachusetts Medical School, Worcester, Massachusetts

Correspondence: For reprints contact: Michael A. Davis, MD, ScD, Dept. of Radiology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655.

ABSTRACT

Radiation synovectomy, a noninvasive therapeutic alternative to surgical synovectomy, has not gained widespread acceptance in the United States because of the lack of a suitable radiopharmaceutical. Two new radioactive particles, [⁹⁰Y]Ca oxalate and [⁹⁰Y]ferric hydroxide macroaggregates (FHMA), were developed in our laboratory and evaluated for size, stability, and joint leakage. More than 90% of the [⁹⁰Y]Ca oxalate particles were in the optimal size range of 1–10 µm, and the unbound activity in serum and synovial fluid was 3.7% to 5.0%. Following injection in rabbit knees, leakage of [⁹⁰Y]Ca oxalate was 5 ± 2%, with localization primarily in the bone and virtually no uptake by the lymph nodes or liver. Yttrium-90 FHMA particles were larger (95% > 10µm), and at least on a microscopic level, appeared to distribute homogeneously over the articular surface. Leakage of [⁹⁰Y]FHMA was initially less but eventually slightly exceeded that of [⁹⁰Y]Ca oxalate. Nevertheless, both radiopharmaceuticals can provide a satisfactory therapeutic dose to the knee with less than half the leakage and a marked reduction in absorbed dose to nontarget tissues compared to previously tested agents. Ease of preparation, physical characteristics of the ⁹⁰Y beta ray, and apparent lack of substantial leakage from the joint make these agents extremely attractive for clinical evaluation in rheumatoid arthritis patients who are unresponsive to medical therapy.