Hi Dr. Landolfi;
Here is the next question from the group. First though, I want to pass on the sincere "thanks" expressed by many of the group members for your assistance.
What are the differences between cyberknife and gamma-knife? Is one better than the other? Why?
Thank you (as always)
Bruce
The doctor's response...
This is not going to be a short answer. Radiosurgery is a single session stereotactic(using points of reference to direct the beam)radiation treatment directed at a particular lesion. If more than a single session, it is stereotactic radiotherapy. It can be done to the head, lung, liver, etc.
There are several machines available. Most are developed from linear accelerators ( a regular radiation machine used routinely for whole brain or conformal radation; also used for the body. They put an adapter on the machine so they can get a single beam of focused radiation to treat a lesion- thus, radiosurgery. In order for the fine beam to treat an entire lesion, the patient (on a bed gantry), the machine, or both must be moved about. Cyberknife is based on linac technology. There is a single beam delivered to the leaion and the machine moves around the patient to treat the whole lesion. The patient does not move. They wear a plastic mask over their head to attempt to keep the head still during treatment so the correct area is treated. They have an accuracy of .9 - 1.3 mm. Because the power sources (radiation sources) of the machine are weak compared to other technologies, the treatemtnt can last several hours. At times the physicians will be forced to spread the treatment over several days(fractionation)- thus no longer stereotactic radiosurgery, but rather stereotactic radiotherapy. Since there is no frame to keep the patient still, the machine checks the patient position and ten seconds later delivers the dose. I feel this is a significant amount of time where the patient can move. In addition, a single beam is used with the full power of that beam going through the patients hair, skin, bone and normal brain. The only way to reduce the full effect of this dose on normal tisue and allow healing, is to divide the dose over several days-thus radiotherapy. Cyberknife has good utility for spine lesions. In this case, fiducials or markers are implanted surgically under the skin. Other linac based systems include x-knife and brain lab.
Gamma Knife is not based on linac tecnology. It was developed in the fifties with the first patient being treated in 1958. Upgrades occur yearly to keep the machine on the cutting edge and is considered the gold standard for radiosurgery. Gamma knife is not fractionated( spread over several days), but is always radiosurgery-a single session treatment. Gamma Knife was developed by a neurosurgeon and a physiciast and is specificaally designed for the brain. It uses cobalt as the radiation sources and is a more powerful machine compared to other technologies. As a result, treatment time is significantly shorter. A frame is place on the head so there is no chance for the patient to move. There are no moving parts to the machine. Everything is stationary which lends to is accuracy of .3 mm. It can not be used for the spine or other parts of the body. Is is designed specifically for the brain alone. It uses 201 beams of radiation directed to a lesion. Each individual beam is weak (this goes thru the hair, skin, bone and normal brain)- a fraction of the total of the beams. Where the beams collide is the full forcef the radiation- directly on the lesion. This reduces the risk to normal tissue and allows a single session treatment. It is so accurate it can be used for individual nerves-trigeminal neuralgia. Linac systems are not adequate to do this, although cyberknife is starting to do this to see the overall affects. I am partial to Gamma Knife. We have the onlt one in New Jersy at presenr. It is not because we have one that I am an advocate. Years ago, because of our large number of trigeminal and brain tumor patients, we decided to get rid of the old linac machine and buy another. This was to be able to offer our patients a variety of different treatments. We chose Gamma Knife becuse of the above.
The bottom line- if I treated a lesion radiosurgically with cyberknife or gamma knife, the control rate would probably be the same. There are no direct comparisions with cyberknife. Other linac based systems have been compared to gamma knife. The control rates were slightly better with gamma knife, but it was not statistically significant. The difference comes in treatment time which is shorter with gamma knife and side effects, decreased with gamma knife because of lower affects on the normal tissue.
Dr. Landolfi