Microbrachytherapy using holmium-166 acetylacetonate microspheres: A pilot study in a spontaneous cancer animal model

Abstract Purpose Holmium-166 acetylacetonate microspheres (166 Ho-AcAc-MS) are proposed as an intratumoral radioablation device. This article presents a pilot study in housecats with unresectable liver cancer. Feasibility and tolerability of intratumoral administrations of166 Ho-AcAc-MS was investigated. Methods and Materials Three cats with unresectable liver tumors of different histotype were included. One cat had hepatocellular carcinoma (HCC), one had cholangiocarcinoma (CC), and one had a malignant epithelial liver tumor (MELT) of unspecified histotype.166 Ho-AcAc-MS were injected percutaneously under ultrasound guidance into the tumors. Followup consisted of physical examinations and hematologic and biochemical analyses. Results166 Ho-AcAc-MS were administered to three liver tumor-bearing cats. The treatment was well tolerated and the clinical condition, that is body weight, alertness, mobility, and coat condition of the animals improved markedly. Most biochemical and hematologic parameters normalized shortly after treatment. Life of all cats was extended and associated with a good quality of life. The HCC cat that received 33-Gy tumor-absorbed dose was euthanized 6 months after the first administration owing to disease progression. The MELT cat received 99-Gy tumor dose and was euthanized 3 months posttreatment owing to bacterial meningitis. The CC cat received 333 Gy and succumbed 4 months after the first treatment owing to the formation of a pulmonary embolism. Conclusions Percutaneous intratumoral injection of radioactive166 Ho-AcAc-MS is feasible in liver tumor-bearing cats. The findings of this pilot study indicate that166 Ho-AcAc-MS may constitute safe brachytherapeutic microspheres and warrant studies to confirm the clinical utility of this novel brachytherapy device.