Experimental studies on interstitial microbrachytherapy with holmium-166 microspheres.
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INTRODUCTION: The treatment of brain cancers is a major challenge in the veterinary and human medicine. Despite the different treatment possibilities the prognosis is still poor. Advances in biomolecular diagnostics of cancer genes, and improvements in microsurgical techniques, radio-, immuno-, gene-, and chemotherapy hopefully will increase survival time of patients diagnosed with malignant disease such as glioblastoma. A promising alternative treatment could be internal radiation therapy, using radioactive holmium microspheres. LITERATURE STUDY: The best treatment strategy for brain tumors, until now, is surgical resection in combination with radiotherapy and chemotherapy. Still the prognosis remains poor, median survival time of nine months. Y-90-biotin as treatment for glioblastoma has superior results, median survival time of 33.5 months. Holmium-166 is a new isotope and has favorable characteristics compared to 90Y. Interstitial microbrachytherapy with Holmium-166 may be a potentially selective treatment for brain tumors. PRACTICAL RESEARCH STUDY: Different sizes of holmium-166 particles are injected into ex vivo canine brain tissue, to evaluate their distribution after intratumoral injection, comparing holmium chloride, 100 nm Ho-AcAc nanoparticles (NP), 8 μm Ho-AcAc-MS and 30 μm Ho-PLLA-MS. MRI and gamma scintigraphy successfully displayed the holmium hotspots and showed a localized distribution. PATIENTS STUDY: Holmium microspheres are used for interstitial microbrachytherapy in veterinary patients with different inoperable tumors. Nine weeks post-treatment complete tumor remission was achieved in a 13-year-old European shorthair cat with a squamous cell carcinoma on the tongue. DISCUSSION: The distribution on the different holmium formulation in ex vivo canine brain tissue is not comparable with the in vivo situation. In this pilot study the holmium-166 appears to be distributed locally. The study design seems to be largely useful for future studies on this matter. Furthermore, interstitial microbrachytherapy by using holmium-166 microspheres appears to be applicable in animals with oral squamous cell carcinomas. CONCLUSION: Multimodality treatment of brain malignancies is recommended, and involves surgery, radiotherapy and chemotherapy. The results of the study on the distribution of different sizes holmium-166 in canine brain tissue and the use of holmium-166 microspheres in veterinary patients are promising, but more research should be done before any conclusions can be made.