Selective internal radiotherapy: microdosimetry, clinical research and patient advocacy
1University of Oxford, Oxford, UK,2CRUK-MRC Oxford Institute for Radiation Oncology, Oxford, UK
Knowledge that liver tumours preferentially take their blood from the host's arterial blood supply rather than the portal venous system can be used for local delivery of treatment or for embolisation to cut off the blood supply to tumours. Over the past two decades, this fundamental knowledge has resulted in the development of new ways of delivering brachytherapy to tumours via their arterial blood supply using radioisotopes such as yttrium-90 and holmium-166. Selective internal radiation therapy (SIRT) of primary or secondary liver malignancies can be performed with yttrium-90 microspheres, a treatment also termed radio-embolisation. Differences in the dosimetry that can be achieved between resin and glass microspheres will be discussed in this talk. Patient advocacy has resulted in these medical devices being evaluated by the NHS via the Commissioning through Evaluation programme. Using SIRT as an example, registry-based models to accelerate the introduction of new medical technologies will be discussed. Finally, the extensive portfolio of phase III clinical studies of SIRT in metastatic colorectal cancer and hepatocellular carcinoma will be summarised. Results from patients who have proceeded to liver surgery following SIRT confirm that the principal mechanism of action appears to be via arterially directed delivery of highly radioactive microspheres in and around the vascular tumour bed rather than by micro-arterial embolisation.