This research is being done with the aim of developing a more effective treatment than standard radiotherapy and surgery alone. Although standard treatment is frequently successful, some patients do not respond well to this treatment. Low oxygen levels in tumours, which may be a particular problem with sarcomas, are thought to be one factor that contributes to failure of radiotherapy. Sunitinib is a new drug that is active against cells with low oxygen levels. The combination of sunitinib and radiotherapy has shown promising results in other cancers. The purpose of this study is to find out whether treatment with a new drug, sunitinib, can increase the effectiveness of radiotherapy at killing cancer cells; to test the safety of the combination of sunitinib and radiotherapy.