Stereotactic technique for localising tumours

Stereotactic radiosurgery is a system that treats brain tumours with greater accuracy, says Mr Peter Whitfield

Stereotactic radiosurgery is a technique that uses three-dimensional surgical localisation techniques to focus high doses of radiotherapy on a suitable treatment target.

The treatment was developed using a gamma knife machine, although in recent years accurate beam shapes are produced from a more conventional linear accelerator (linac) radiotherapy machine using an m3 device to help accurately shape the beam to conform to the target lesion.

The treatment is well established for use in patients with arteriovenous malformations (AVM), acoustic neuromas, metastatic brain tumours and other types of benign brain tumours in difficult surgical locations. It involves the patient undergoing pre-treatment scans.

On the day of treatment the patient has a frame secured to the skull under local anaesthetic. This enables the treating surgeon to accurately determine the location of the target lesion in three dimensions.

This image is fused with the pre-treatment scans enabling the lesion to be identified with the best anatomical accuracy available.

The radiotherapy is then planned minimising the dose of radiotherapy to normal brain but maximising the dose to the target lesion.

Focus on the tumour
For most patients around four beam arcs are used so that the radiotherapy source is rotated around the patient’s head and is focused by the m3 device onto the lesion.

Most patients are treated as a day case, although a few who have had angiograms may stay in overnight.

The technique has been performed an estimated 70 times in Plymouth.

Radiotherapy usually exerts its effects by either stopping cell growth in the case of a tumour or leading to gradual obliteration of the arteries supplying an AVM.

Side-effects
The radiotherapy can damage surrounding structures. Many areas of the brain are relatively resistant to such radiotherapy, however, care has to be taken in the vicinity of the brainstem and the optic pathways to minimise damage. Long-term statistics show that around 80 per cent of treated AVMs are obliterated with stereotactic radiosurgery.

The rates for patients with acoustic neuromas and other benign brain tumours appear to be very high also.

The treatment is an alternative for surgery in patients with single brain metastases and may enable them to avoid whole brain radiotherapy.

Cost and availability
The cost of the m3 machine is an estimated £500,000, and the treatment requires a whole team of clinicians. Stereotactic radiotherapy is available at a few hospitals in the UK.

In Plymouth our team comprises two neurosurgeons, two neuro-oncologists, a neuro-radiologist and our physics and radiotherapy technicians.

The National Centre for Stereotactic Radiosurgery in Sheffield has a vast experience. The Cromwell Hospital, London also has a gamma knife. Linac radiosurgery with the m3 focusing device is only available in Plymouth.

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