Prostate cancers are known to form hypoxic regions. These hypoxic cells are more radio-resistant then well oxygenated tissue and they are often a reason for recurrent tumours in radiotherapy. Furthermore hypoxia enhances malignant progression of the tumour. The ratio of doses under oxic and hypoxic conditions to achieve the same biological effect is called the oxygen enhancement ration (OER). Under normal conditions OER is described as 'dose modifying' i.e. it is constant over the whole dose effect curve. As the OER is strongly LET dependent  a system should be developed that enables the irradiation with X-rays and carbon ions for acute hypoxia.