Skull Base Radiotherapy

Radiotherapy is the use of high energy X-rays to treat tumours. It can be delivered as a single or small number of treatments and this is normally called stereotactic radiosurgery. Alternatively it can be divided into 30 treatments (fractions), which are given daily (Monday to Friday) for several weeks; this is called fractionated stereotactic radiotherapy. To decide which form of radiotherapy is best for you involves an outpatient appointment, look at your MRI scans to assess the size of your tumour, its location and also to consider your own personal preference.

What is the aim of radiotherapy?

Radiotherapy aims to stop benign tumours growing any bigger and for some patients will actually make them shrink, although this may take years following treatment. Radiotherapy in these situations will not remove your tumour. Radiotherapy might also be offered as a treatment after a more aggressive tumour has been excised. Occasionally radiotherapy is offered as palliative treatment to reduce symptoms but not with the intention of cure.

Fractionated stereotactic radiotherapy

The benefits of radiation are not immediate but occur over time. Aggressive tumours, whose cells divide rapidly, tend to respond quickly to radiation. Following radiotherapy, the abnormal cells die and the tumour may shrink. Benign tumours, whose cells divide slowly, may take several months to a year to show an effect.

Radiotherapy is split into a number of treatments called fractions that are given over several weeks. Delivering a small fraction of the total radiation dose allows time for normal cells to repair themselves between treatments, thereby reducing side effects. Fractions are usually given five days a week with a rest over the weekend. Therapy sessions often take less than an hour.

The radiation beams are generated by a machine called a linear accelerator. The beams are precisely shaped to match the tumour and are aimed from a variety of directions by rotating the machine around the patient.

Gamma knife radiosurgery

The Gamma Knife is not a knife in the conventional sense, but uses a focused array of intersecting radiotherapy beams to treat lesions within the brain.

Within the central body of the Gamma Knife there is an array of separate sources and each of these produces a fine radiation beams. The sources are evenly distributed over the surface of the source core so that each beam is directed at a common focal spot – the tumour.

The resultant intensity of radiation at the focus is extremely high whilst the intensity only a short distance from the focus is very low. This enables a high dose of radiation to be delivered to the abnormal tissues whilst sparing the adjacent healthy brain tissue.  Gamma knife treatment usually requires only a single treatment.

Cyber knife

The CyberKnife has X-ray cameras that monitor the position of the tumour and sensors that monitor the patient’s breathing. This enables a robotic arm to reposition the radiotherapy beam during treatment in order to minimise damage to healthy tissue. CyberKnife moves with the patient’s breathing and can track a moving tumour. It is not necessary to fix the head of the patient in a frame, as is required for Gamma knife treatment.

Because of its accuracy, CyberKnife allows larger fractions (doses) of radiotherapy to be delivered, meaning that the patient requires fewer hospital visits. Cyber knife treatment usually requires three treatments.