Ask the Expert

On Cancer: Why Am I Hearing So Much About CyberKnife?

By Jim Stallard, MA, Writer/Editor  |  Monday, February 24, 2014
Pictured: Abraham Wu Radiation oncologist Abraham Wu

Advertisements for a radiation delivery system called CyberKnife® have prompted a large number of questions from patients inquiring whether it employs a unique new technology.

CyberKnife is used in a type of radiation therapy called stereotactic radiosurgery (also known as stereotactic radiotherapy). This treatment destroys tumors with extremely precise, very intense doses of radiation while minimizing damage to healthy tissue, offering accuracy akin to the sharpness of a surgeon’s scalpel.

Memorial Sloan Kettering radiation oncologist Abraham J. Wu employs stereotactic radiosurgery to treat lung and gastrointestinal cancers. He explains that CyberKnife is a brand name for one of several available stereotactic radiosurgery devices that deliver radiation with linear accelerators, or devices that form beams of fast-moving subatomic particles. The beams are precisely directed through the use of advanced imaging technologies combined with a sophisticated computer guidance system.

“There are a lot of different machines and a lot of different marketing terms thrown around, but they all achieve the same goal, which has two critical components,” Dr. Wu says. “One is delivering a more intense dose of radiation in just a few sessions. The other is targeting the radiation very accurately by pinpointing the precise location of the tumor during treatment.”

The Importance of Image Guidance

Memorial Sloan Kettering radiation oncologists use linear accelerators made by a company called Varian. The Varian machine Dr. Wu most often uses — primarily to treat lung tumors — employs a system called TrueBeamTM, which incorporates computed tomography (CT) imaging into the same device that delivers the radiation. This allows the radiation therapists to make sure patients remain in the proper position during radiation therapy and to adjust the radiation beams as needed.

“Really, the big breakthrough in recent years has been the advent of CT imagers on the treatment machine itself — as we have with the TrueBeam — which allows us to ensure the accuracy of radiotherapy treatments with the highest precision,” he says. “Interestingly, CyberKnife does not incorporate a CT imaging machine into the device — it uses a different system of image guidance.”

The main distinguishing feature of CyberKnife is that the linear accelerator is mounted on a robotic arm. While this offers more flexibility and freedom of movement in how the radiation beam is delivered, Dr. Wu says that “in practice this is rarely something that is going to make a difference in how precisely we treat someone. We can still deliver the radiation to a given target.”

What is important, he explains, is the skill and experience of the radiation oncologists and medical physicists who define the radiation target.

“There are a lot of different technical solutions to achieve the kind of accuracy that you need to deliver very high doses of radiation — it’s a variety of different means to the same end,” Dr. Wu says. “We’re convinced that our Varian machines enable us to perform stereotactic radiosurgery at the highest level.”


My daughter is having this procedure next month..

How is this different from proton therapy?

Brenda, thank you for your comment. We consulted with Dr. Wu who provides this response:

Proton therapy means that the radiation is being delivered in the form of protons, a different type of subatomic particle. Both CyberKnife and TrueBeam use x-ray (also known as photon) radiation, which is the most common and best-established way to deliver stereotactic radiotherapy. Protons can sometimes be used to deliver stereotactic radiotherapy, but protons currently are not compatible with the same kind of sophisticated image guidance used in TrueBeam.

My husband has mesothelioma and is going to do proton therapy at md Anderson. He is currently enrolled in a clinical trial with ur hospital. Is this type of technology better than proton?

Brenda, unfortunately, we cannot answer personal medical questions on our blog. Decisions about the best therapy and best technology are based on each individual case, and we suggest your husband consult with his physician on questions such as this.

Ok thanks is much for the work u all are doing. I am so encouraged to hear about all the new technologies. We will discuss this with our radiologist.

Can this type of procedure be used on pancreatic cancer tumors(IPMN)? Thank you.

Barbara, thank you for your comment. Stereotactic radiosurgery as described in this story has been used to treat pancreatic cancer. You can read a recent discussion of it here:

If you would like to make an appointment with a Memorial Sloan-Kettering physician, please call our Physician Referral Service at 800-525-2225 or go to

How does this compare to IMRT and Neutron radiation?

Sylvia, thank you for your comment. We consulted with Dr. Wu and he responded:

We incorporate intensity-modulated radiation therapy (IMRT) into our stereotactic treatments. IMRT is a way of “shaping” the radiation dose in complex ways, while “stereotactic” means that the radiation dose/shape is delivered very precisely. So the two techniques are not mutually exclusive and we combine the two. Neutron radiation is very rarely used for any cancer nowadays, and is not used for stereotactic radiation as far as I know.

can this be used for multiple areas of metastatic prostate cancer disease?

Has this device been used on tumors in the brain?

Mary, yes the devices discussed in the story have been used to treat tumors in the brain, both primary tumors and brain metastases. You can learn more about this treatment here:

(scroll down to the section titled "Brain Metastasis: Single-Day High-Dose Radiation")

We plan to have an updated blog story about this in a few weeks with more detail. Thank you for your comment.

Where can a patient find information about radiation scatter to the heart when undergoing radiation for left breast cancer?

Joan, thank you for your question about radiation treatment of breast cancer. To learn more about how Memorial Sloan-Kettering treats breast cancer, you can go to For questions about breast cancer treatment, you also can call the National Cancer Institute’s Cancer Information Service at 800-4CANCER (800-422-6237). To learn more about the CIS, including Live Chat help and how to send them an email message, go to

I have leiomyosarcoma, I am currently getting IMRT to the sacrum. I had a tumor removed from the sacrum. I had cyberknife last April to a tumor in the liver. It was successful and they said it was gone, however they saw an increase in size in Dec. I am receiving treatment at Sara Cannon in Nashville. Is there a better treatment? I have had several surgeries and now it is back in my lungs again. I need some help determining the best treatment.

Dear Brenda, we are sorry to hear that the cancer is back. Unfortunately, we cannot answer personal medical questions on the blog. If you would like to make an appointment for a consultation with one of our specialists who can provide a personalized assessment of your treatment options, please call our Physician Referral Service at 800-525-2225. Thank you for reaching out to us.

I had this type of procedure for an acoustic neuroma 5 years ago. At the time, not a lot of data was out there in regards to long term effects. Has more data surfaced since then?

Michele, thank you for your comment. We are looking into finding an expert who can provide a response for your particular question.

Michele, we consulted with MSK physician Josh Yamada, who responded:

There are several large patient series (University of Pittsburgh, and the UK series, for example) with long term follow up suggesting the radiosurgery for this type of tumor has an extremely low incidence of serious complications.

I have metastatic colon cancer and there are very small lesions on my lungs. ( a few cms and less) Is this type of treatment available to treat small lesions?

Susan, we passed your question on to Dr. Wu and he responded:

Yes, SRS is frequently used to treat metastatic lesions in the lungs and other organs. Usually it is only recommended when there are a limited number of lesions (~3 or less), and the lesions are relatively small (~5cm or less), but it is always on a case-by-case basis.

Thanks for the reply. This is food for thought when considering the future of my treatment. What is the recovery like from this treatment on the lungs?

Susan, who passed your question on to Dr. Wu, who responds:

Most patients do not have any noticeable impact from this treatment on the function of their lungs. Often, the only noticeable side effect from SRS to the lungs is fatigue. There is, however, a small risk of developing a lung complication that can affect your breathing, as well as other risks that would have to be discussed with the radiation oncologist.

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