Dosimetry of a 90Y-hydroxide liquid brachytherapy treatment approach to canine osteosarcoma using PET/CT

A new treatment strategy based on direct injections of 90Y-hydroxide into the tumor bed in dogs with osteosarcoma was studied. Direct injections of the radiopharmaceutical into the tumor bed were made according to a pretreatment plan established using 18F-FDG images. Using a special drill, cannulas were inserted going through tissue, tumor and bone. Using these cannulas, direct injections of the radiopharmaceutical were made. The in vivo biodistribution of 90Y-hydroxide and the anatomical tumor bed were imaged using a time-of-flight (TOF) PET/CT scanner. The material properties of the tissues were estimated from corresponding CT numbers using an electron-density calibration. Radiation absorbed dose estimates were calculated using Monte Carlo methods where the biodistribution of the pharmaceutical from PET images was sampled using a collapsing 3-D rejection technique. Dose distributions in the tumor bed and surrounding tissues were calculated, showing significant heterogeneity with multiple hot spots at injection sites. Dose volume histograms showed that approximately 33.9% of bone and tumor and 70.2% of bone marrow and trabecular bone received an absorbed dose over 200Gy; approximately 3.2% of bone and tumor and 31.0% of bone marrow and trabecular bone received a total dose of over 1000Gy. Treatment of canine osteosarcoma using 90Y-hydroxide using localized liquid brachytherapy. A 3-D co-registered PET/CT image showing the distribution of 90Y in the left tibia of a dog with osteosarcoma. Multiple high activity hotspots are shown within bone marrow and isolated hotspots within the tumor bed, corresponding to the sites of administration. Absorbed doses were estimated to be as high as 2000Gy to tumor. [Display omitted] •A liquid brachytherapy treatment of canine osteosarcoma using 90Y hydroxyapatite is presented.•Dosimetry of 90Y hydroxyapatite liquid brachytherapy was carried out using PET-CT.•Activity distribution correlated with site of injections while spearing bone marrow.•Dose distribution showed significant heterogeneity with multiple hot spots.•Approximately 3.2% of tumor tissue received a total dose of over 1000Gy.