Radiation synovectomy with holmium-166 ferric hydroxide macroaggregate in equine metacarpophalangeal and metatarsophalangeal joints

Histo-morphological effects on equine synovium after arthroscopic synovectomy using two different motorized synovial resectors and two different intensities

The purpose of the study was to determine the histo-morphological effects on villous synovium after synovectomy using two different motorized synovial resectors and two different intensities ex-vivo. Thirty-three (n = 33) equine metacarpophalangeal/metatarsophalangeal joints were used. Synovectomy was performed along the dorsomedial/dorsolateral synovium (n = 66) using two motorized synovial resectors (aggressive full radius resector, AFRR, used at two intensities: single treatment, n = 24 vs. triple treatment, n = 21 vs. aggressive meniscus side cutter, AMSC, n = 21). Arthroscopic images were evaluated blindly for resector type and intensity. Histological images were evaluated descriptive for synovial morphology and the extent of tissue loss using a microscopic scale. Scanning electron microscopy described the synovial morphology. The synovectomized areas were specific for each resector used and distinguishable from arthroscopic images. The AFRR demonstrated a clear demarcation between treated and non-treated areas and removed the stratum synoviale completely including parts of the underlying stratum fibrosum. In contrast, the AMSC showed less clear demarcation, villous scaffolds and no involvement of the stratum fibrosum. Triple intense treated AFFR samples resulted in significantly deeper lesions compared to single treatments (p = 0.037) but could not be distinguished on arthroscopic images. The morphological effects on villous synovium differ according to the resector type used. The extent of synovial tissue loss cannot be estimated from arthroscopic images but histologically. The type and use of motorized synovial resector determines the morphological alterations of the treated synovium. Arthroscopic control is considered unsuitable to control synovectomy depth.

The future of radiosynoviorthesis: bright or bleak?

Radiosynoviorthesis (RSO) is a decades known, effective intra-articular nuclear medicine local therapy, with few rare side-effects, in which inflamed synovial membrane is treated by means of colloidal beta-emitters. There are major variations worldwide in terms of acceptance, frequency of use and approved indications for this procedure. Thus, reliable figures that reflect reality are only available for a few countries. A Europe-wide survey revealed that RSO is carried out most frequently in Germany, where RSO is the most common nuclear medicine therapy with about 70,000 joints treated per year. The main indications include synovitis due to rheumatoid arthritis, hemophilia and pigmented villonodular synovitis (PVNS), and depending on national approvals, osteoarthritis. Despite the many indications, there are very few published scientific studies and therefore, RSO evidence is lacking. Reliable data on the clinical usage of RSO and demographics of RSO specialists are only available in Germany, thus we discuss the future challenges of RSO mainly from a German perspective. In the German healthcare system, RSO is performed primarily on an outpatient basis and plays only a minor role in the university setting. The necessary expertise for RSO is therefore lacking, for the most part, at university training centers. Currently, nearly more than three quarters of the German RSO experts are over fifty years old, illustrating a shortage of young talent. In the future, RSO providers from the non-university or private sector will have to cooperate with universities through networks and will have to intensify their cooperation with referring physicians, such as rheumatologist and orthopedic surgeons, and patients in order to maintain a timely and beneficial exchange of information. In networks of RSO experts, the participants must jointly develop and establish training concepts and facilities for future talents, elaborate on guidelines, if clinically useful expand the range of indications, initiate studies to generate further evidence and finally make the procedure more public. In addition, it is worthwhile to apply this process beyond human medicine to other fields, such as medical physics and veterinary medicine. If these points are implemented, the future of RSO will be bright, if it fails, it looks bleak.

The various therapeutic applications of the medical isotope holmium-166: a narrative review

Over the years, a broad spectrum of applications of the radionuclide holmium-166 as a medical isotope has been established. The isotope holmium-166 is attractive as it emits high-energy beta radiation which can be used for a therapeutic effect and gamma radiation which can be used for nuclear imaging purposes. Furthermore, holmium-165 can be visualized by MRI because of its paramagnetic properties and by CT because of its high density. Since holmium-165 has a natural abundance of 100%, the only by-product is metastable holmium-166 and no costly chemical purification steps are necessary for production of nuclear reactor derived holmium-166. Several compounds labelled with holmium-166 are now used in patients, such Ho¹⁶⁶-labelled microspheres for liver malignancies, Ho¹⁶⁶-labelled chitosan for hepatocellular carcinoma (HCC) and [¹⁶⁶Ho]Ho DOTMP for bone metastases. The outcomes in patients are very promising, making this isotope more and more interesting for applications in interventional oncology. Both drugs as well as medical devices labelled with radioactive holmium are used for internal radiotherapy. One of the treatment possibilities is direct intratumoural treatment, in which the radioactive compound is injected with a needle directly into the tumour. Numerous other applications have been developed, like patches for treatment of skin cancer and holmium labelled antibodies and peptides. The second major application that is currently clinically applied is selective internal radiation therapy (SIRT, also called radioembolization), a novel treatment option for liver malignancies. This review discusses medical drugs and medical devices based on the therapeutic radionuclide holmium-166.

Dosimetry perspectives in radiation synovectomy

Rheumatoid arthritis (RA) is a chronic inflammatory disease that can potentially damage the synovial joints. One of the effective treatment modality for RA is radiation synovectomy (RSV) where properly selected radionuclide is injected into the joint space, enabling controlled destruction of diseased synovial membrane via radiation exposure. Radiation dosimetry in RSV appears challenging due to the heterogeneous nature of synovial membrane, nonuniform distribution and leakage of radionuclide from the synovial cavity. This article reviews the dosimetric perspective pertaining to RSV. Specifically, characteristics of radionuclide for RSV and radiation dose to target and non-target (i.e., articular cartilage, bone, bloodstream, gonads, etc.) tissues of patient have been discussed. The personal dose H_p(0.07) to the hands of medical staff (i.e., radiochemist, therapist physician, nurse) may be considerably high due to handling of high specific activities (∼500 MBq/ml for Y-90); such doses are typically measured using thermoluminescence dosimeters (TLD) ring dosimeters and ranges from 1 to 21.5, 0.1 to 40 and 0.1 to 5 µSv/MBq for the radiochemist, therapist physician and the nurse, respectively. Methods to minimize radiation doses to the patient, medical staff and public are elaborated. Contamination risks and precautionary measures are also reported.