Radiosurgery is a treatment method for treating brain tumours with radiation, to kill the tumour cells or to attempt to restrict their capacity to grow. Whilst this treatment does not remove the tumour, it may cause some shrinkage over time, and it is often advised to treat deep-seated tumours that may be difficult to reach or remove by surgical methods. Radiosurgery is available in the UK in a few specialised neurological centres and can be carried out by Gamma Knife, by modified linear accelerator (Linac), or by CyberKnife©.
The word stereotactic means locating a site using three-dimensional coordinates, usually captured by modern day imaging techniques, and it is this that assists practitioners to hone in on the precise point of the tumour.
Gamma Knife is a device that has been designed specifically for radiosurgery for brain tumours and any other abnormality of the brain. It uses 201 gamma rays that combine to form a high-energy point at the focus, with each ray being too individually weak to damage the healthy brain tissue in its path or surrounding areas.
A linear accelerator uses multiple beams of high-energy radiation, again targeted to the tumour. Most linear accelerators are used to treat general cancerous and noncancerous abnormalities in the body. However selected machines can be specifically adapted on a per patient basis to enable stereotactic treatment delivery.
While CyberKnife© is a linear accelerator device, as with the Gamma Knife this machine has been designed specifically for radiosurgery. In this latest technology the Linac is mounted on a robotic arm which delivers around 150 to 200 beams, each sent from a different unique angle, pinpointed to the tumour site as the machine continually x-rays during treatment, directing the focus through sophisticated software.
Stereotactic Radiosurgery (SRS) is the general medical term used today for administering radiation to treat conditions of the head and brain. SRS can be delivered in one treatment dose or in smaller doses over a number of sessions. This may even take a few weeks with small daily doses.
When radiosurgery is delivered as a course of treatment, each individual small dose is referred to as a ‘fraction’ of the overall measure, and was previously known as ‘fractionated radiosurgery’. All doses, whether in single or multiple parts, are calculated based on the size of the tumour, and the treatment level is therefore individualised to the patient and the acoustic neuroma itself.
Due to the requirement for absolute accuracy in administering radiosurgery, patients must remain motionless during treatment, and a variety of means are used depending on the device. For Gamma Knife treatment, a metal frame that attaches to the device is measured to the size of the patient’s head and fitted directly to the skull following localised anaesthesia. Due to the fitting of this frame, Gamma Knife is delivered in one dose and cannot be fractionated.
A variety of methods can be used to keep patients still with Linac treatments including a metal frame similar to Gamma Knife, a thin plastic mask applied over the face, or a mouth bite device moulded according to the patient’s teeth. The plastic mask and mouth bite are only used during treatment and permit both single or multiple treatments (fractionated). The mask is made from a fine breathable mesh, which when warmed is placed over the head and face, where it forms an individual mould that sets in place once cool. While this mask is held down to the treatment table, it is not directly attached to the patient. Patients treated with the CyberKnife system will wear plastic masks and the machine adapts to compensate for small movements in patient position during treatment delivery.
An overnight stay in hospital is generally not required for radiosurgery treatments and some people are able to return to their normal routine immediately afterwards.
Not all acoustic neuromas are suitable for stereotactic radiotherapy and in most units 3cms would be the maximum size of tumour that is suitable for this treatment. The treatment does not eradicate the tumour, which remains as it is relatively radio-resistant. However, there is an extremely high chance that it will stop the growth of the tumour (90-95%).
The fact that the tumour is still there may result in a degree of anxiety along with the unknown state of its size in the period between scans. The aim of this treatment is to stop the tumour growing and careful monitoring by MRI scanning is necessary after the treatment.
The effect of the radiation on the tumour will often increase the size of the tumour in the short term which can increase some symptoms until the tumour shrinks down. As with watch, wait and rescan patients, some symptoms will remain, such as hearing loss, tinnitus and balance problems, and the risks include an increase in these symptoms. This is important in the context of the person’s quality of life. The risks of radiotherapy include facial pain and headaches and all of these will be described in detail by the doctor.
Listen to BANA member Julia talk about her GammaKnife/AN experience by clicking here
Information for review September 2016