Stereotactic radiosurgery is a technique to precisely deliver therapeutic radiation to a target within the nervous system while minimising the dose of radiation to adjacent tissue. This reduces the side effects of therapy and allows for repeated treatments in selected cases as well as safer treatment of multiple targets simultaneously e.g. brain metastases.
Unlike radiotherapy which often seeks to arrest cell division by damaging the reproductive ability of the cell at the DNA level. Radiosurgery seeks to physically destroy the cells in-stu. Multiple beams of radiation which individually pose little if any risk of injury are delivered from multiple directions to a target which receives the sum of their energies.
Stereotactic refers to the use of a three-coordinate system to describe the position of the target lesion in a patient and correlate it to a virtual target generated from patient imaging. Originally this relied on the application of a frame directly to the patient's head but it is also possible to use a mask or robotic positioning systems to achieve a similar accuracy. In most cases radiosurgery can be delivered under a local anaesthetic if any anaesthetic is required and treatment will often not require hospital admission.
The Gamma Knife is perhaps the best established radiosurgery platform worldwide. It delivers high-intensity gamma radiation to the target originating from 201 Cobalt-60 sources arrayed around the patient's head. It was developed by Swedish neurosurgeon Lars Leksell together with Ladislau Steiner, and Börje Larsson
Modern Gamma Knife systems can also be used without the need for a frame although in some situations its use is recommended to aid accuracy.
The CyberKnife delivers radiation in a different way to the Gamma Knife. It is a Linear Accelerator (LINAC) based platform meaning that the type of radiation emitted is high energy x-ray or photons. In the CyberKnife the LINAC radiation source is married to a robotic mount. Realtime fluoroscopy (continuous x-rays) allows computer adjustment of the target while small movements occur. Consequently the rigidly fixed frame described above is not required something which makes this platform particularly useful for targetting lesions in the spinal cord and column. Instead a closely fitting mask is made for each patient ahead of treatment. Risks are similar to other varieties of sterotactic radiosurgery.
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