Intraarticular injection of a Tin‐117 m radiosynoviorthesis agent in normal canine elbows causes no adverse effects

Abstract

This longitudinal prospective exploratory study used serial measurements in five dogs to evaluate safety and retention of a tin-117 m ( 117m Sn) colloid after intra-articular injection in normal elbow joints. Each dog was deemed healthy based on physical examination, laboratory results, and radiographic evaluation of both elbows. While anesthetized, each received an MRI of both elbows, followed by fluorine-18 fluorodeoxyglucose positron emission tomography scans of both elbow joints and associated lymph nodes. Joint fluid (0.5-1.0 mL) was withdrawn aseptically from the left elbow joint, followed by intra-articular injection of 117m Sn colloid (92.5 MBq; 1-1.5 ml). Postinjection assessments included blood counts, serum chemistry panels, urinalyses, radiographs, joint fluid analyses, MRI/positron emission tomography scans, scintigraphy, and biodistribution scans. On day 45-47, each dog was euthanized and a complete postmortem examination was performed. Tissue samples were submitted for histopathology and radioisotope retention studies.Left elbow joints were decalcified and sectioned for future autoradiography. Scintigraphy, 1 day after injection, indicated slight radioisotope escape from the joint to regional lymph nodes. Serial blood, urine, feces, and organ counts indicated >99.1% of the 117m Sn activity was retained in the joint for 45-47 days. Radiation output levels were below patient release levels the day following injection. Maximum standard uptake value for the injected joint decreased. Joint fluid cytology was unchanged. No dog exhibited lameness during the study. Absence of joint damage and lack of systemic effects after injection of the 117m Sn colloid in normal canine elbow joints indicate that this agent may be safely used for radiosynoviorthesis in dogs with osteoarthritis. K E Y W O R D Sarthritis, radiation therapy, radioisotope, synovectomy

Prospective Clinical Evaluation of Intra-Articular Injection of Tin-117m (117mSn) Radiosynoviorthesis Agent for Management of Naturally Occurring Elbow Osteoarthritis in Dogs: A Pilot Study

“…The absence of any adverse effects in the present study and in a previous experimental study, is most likely due to unique characteristics of 117m Sn. 23 , 25 , 26 Tin 117m emits abundant conversion electrons, low-energy particles with a short, non-diminishing penetration range of approximately 300μm in tissue. Other radionuclides that emit beta particles result in variable tissue penetration and can result in damaging irradiation of adjacent non-target tissues.…”

“… 24–26 In a recent prospective safety study of 5 dogs, blood, urine, feces, and organ scintigraphy counts showed that >99% of 117m Sn activity was retained in the elbow joint for approximately 6–7 weeks. 23 There were no adverse effects, and post-mortem evaluation revealed no joint damage. These findings, combined with the potential for protracted clinical improvement after a single IA injection, justify further evaluation of 117m Sn for the management of canine OA.…”

“…The homogeneous 117m Sn-colloid (Synovetin OA ® , Exubrion Therapeutics, Buford, GA) was injected into the joint as previously described. 23 After completion of the injection, dogs were recovered from anesthesia and discharged the following morning. Instructions for care and handling with regards to the radioisotope were provided to the owners.…”

“…Previous studies in both laboratory rats and dogs in which histologic sections were obtained have shown that even with higher doses of homogeneous Tin 117m colloid, “beta burns” did not occur. 23 , 25 Standard industry precautions were taken when handling homogeneous tin colloid as with any unsealed radiation source as prescribed by the Nuclear Regulatory Commission.…”

“… 22 Tin 117m ( 117m Sn) homogeneous colloid was specifically developed to avoid the serious outcomes following treatment with high-energy beta emitters. 23 Tin 117m colloid is a non-beta emitter with lower energy from which the conversion electrons have a therapeutic distance of activity of only 300 microns (0.3 mm).…”