Radiotherapy given in standard fractionation regimes leads to cell death by causing double stranded DNA breaks via production of oxygen free radicals. At the very high doses of stereotactic body radiotherapy (SBRT) administered with extreme accuracy in a single fraction by the CyberKnife system, there is induction of tumour necrosis due to endothelial cell damage and vascular collapse, cell membrane breakdown, and the release of cellular material and tumour antigens into the circulation, in addition to DNA strand breaks. It is hypothesised that the combination of modulation of the body's immune responses in the presence of an increased exposure to tumour antigen will provide sufficient induction of the immune system to suppress tumour growth.