With the progress of technology, radiation oncology grew from a 2-dimensional to a 3-dimensional planning system. This specific type of technology which uses external beam radiation planning takes into account the 3 dimensional information of a cancer tumour, i.e. its volume and the nearby organs at risk. Treatment planning is conducted using the CT simulation of the patient in a particular position with particular immobilisation devices. Then, images are transferred to a planning station where the tumour is marked out from any other organs at risk. Eventually, the dose is prescribed by the radiation oncologist. The whole process is computerised and an appropriate plan is made for delivering the patient’s cancer treatment.