The Gamma Knife can remove brain tumours and repair abnormal arteries while leaving the skin intact. Just as keyhole surgery has taken over from open surgery, the Gamma Knife marks the start of no-hole surgery.
The device focuses a beam of intense radiation at the precise spot inside the skull where the tissue to be destroyed, such as a brain tumour, is located. The dead cells are removed by natural processes and carried away in the blood.
The treatment, known as radiosurgery, is painless, lasts five to fifteen minutes, and allows the patient to return to work next day. A conventional brain operation takes several hours under general anaesthetic followed by intensive care and a long convalescence.
Christer Lindquist, neurosurgeon at Cromwell Hospital, London, who will operate the machine, said: "The idea is to deliver a killing dose of radiation at one single time without injuring the surrounding tissue. This is at the frontier of technology for non-invasive treatments."
The development of the machine marks the growing importance of engineers in hospitals. The era of heroic surgery in which patients are opened up and their internal organs rearranged is passing into history. Surgeons increasingly rely on hi- tech instruments, some operated by robots, inserted through tiny incisions, or no incision at all. As one expert put it: "We have got to get away from the idea that when something goes wrong you make a bloody great hole, put your hands inside and sort it out. Our grandchildren won't believe that is what we did."
The Gamma Knife focuses 200 separate rays of radiation in the head. The rays are beamed through holes in a metal helmet like a colander. Each is too weak to cause damage as it passes through the skin and brain, but focused together on a single point they destroy tissue in that area.
The success of the device depends on the accuracy of the targeting system. If the wrong tissue is destroyed, the consequences could be disastrous. The head is held rigid in a metal frame that is screwed (under local anaesthetic) into the skull, and a computerised imaging system establishes co-ordinates for the tissue to be destroyed. In the case of cancer it is essential that the whole tumour is eliminated.
The device has been tried for the treatment of liver cancer, spinal tumours and pancreatic cancer. Its use is limited by the need to hold the target organ rigid, though that may change in future.
Radiosurgery is different from radiotherapy, which delivers a lower dose of radiation to a wider area to mop up any cancer cells remaining after conventional surgery. Radiotherapy relies on the biological principle that healthy cells recover after a (relatively) low dose of radiation but cancer cells do not. The Gamma Knife uses a much higher dose of radiation, which destroys both healthy and cancer cells.
However, in the case of cancer, it is suitable only for secondary brain tumours that have spread from elsewhere in the body and are well defined in the brain. Primary brain tumours throw off malignant cells, which cannot be mopped up by the radiosurgery technique.
The pounds 2.5m machine acquired by the private Cromwell Hospital is the first to be installed in Britain exclusively for clinical use. It will be available to NHS patients at a cost of pounds 7,000 to their health authorities. An older machine has been used in trials at Sheffield University, chiefly for arterial malformations of the brain. Worldwide, an estimated 80,000 patients have been treated.