Cyberknife for Prostate Cancer
What is Cyberknife and how can it be used to treat prostate cancer?
CyberKnife is a robotically controlled radiation delivery machine. It was developed about 10 years ago primarily as a devise to deliver
for tumors of the brain. SRS has been used for over three decades to treat brain tumors. With this technique multiple (on the order of 200) separate beams or a moving beam of radiation is focused on a tumor. The beam(s) is very narrow so there is a very large amount of radiation that is delivered to a very small area in the brain. The aim is to use such a high dose of radiation that the tumor is
or basically destroyed. This has to be performed with great precision. In the past, patients where placed in tight head holding devices so the beam(s) of radiation could be properly targeted on the tumor area. The Cyberknife device takes standard X-ray images during the treatment without the head holding (
) device to target the brain tumors. In the last 7 years, this technology has been augmented so it can be applied to other parts of the body including the prostate for men with prostate cancer. It is important to understand that Cyberknife for prostate cancer is
a new form of radiation, it is using a
designed to deliver high energy X-rays to prostate. The X-rays coming out of the Cyberknife machine are the same type that are used for standard external beam (with IMRT or IGRT).
What Happens When Cyberknife is used to Treat Prostate Cancer?
There are two parts to the Cyberknife treatment which are unique. The first is the radiation machine. The Cyberknife is basically a large robotic arm. This robot is designed to carry a heavy load and move with sub millimeter precision. Attached to the robot arm is a mini radiation machine (also called a LINAC). Unlike the standard machines with are very large and weigh several tons, this mini-LINAC is relatively small and weighs only a couple of hundred pounds. Both types of machines deliver high energy X-rays which have been used for over 50 years to treat cancer.
The second feature of the Cyberknife machine is the real time tracking of the target
the actual radiation treatments. No other device has this capability. The Cyberknife machine basically adjusts in real time to the position of the prostate. Prior to prostate cancer Cyberknife treatments, a Urologist places into the prostate 4 very small slivers of gold. These pieces of gold are called
This is done in a procedure very much like a prostate biopsy. About a week or so after these markers are placed the patient undergoes a CT scan (and in most people a MRI too). These scans are used to develop a plan to deliver the radiation with the Cyberknife . The patient returns the following week to begin their Cyberknife treatments. Each treatment entails lying on a table while the robotic arm moves the mini-LINAC to about 200 positions. At each position a small amount of a narrow beam of radiation is delivered to the target, in this case the prostate. All these beams are focused on the prostate. X-rays are taken during the treatment and a computer identifies the 4 gold markers in the prostate. If the prostate moves or even jiggles during the treatment, the robot adjusts for this motion. Each treatment only takes about 45 minutes. Depending on the situation, 2 or 5 treatment are used. This compares to 4-9 weeks of standard external beam even using IMRT or IGRT techniques.
What are the reasons for Cyberknife's use to treat prostate cancer?
There are two main reasons why Cyberknife is a very attractive approach to treat prostate cancer. One is theoretical the other is based on long term data. The Cyberknife approach is to use only a few high dose treatments to treat prostate cancer as opposed to many low dose treatments (as is done with standard external beam-IMRT/IGRT) or with continues low irradiation (as is done with "seeds" or low dose rate brachytherapy). The technical term for this is "
accelerated hypofractionation." There is evidence from how prostate cancer cells respond to radiation that accelerated hypofractionated radiation is better at killing prostate cancer. Based this
mathematical model the dosing for Cyberknife prostate cancer treatment where developed. It must be emphasized that these calculations are based on a
model and is not proven. However, this
model has been used for over 25 years to develop various radiation dosing schedules.
The second line of evidence that
accelerated hypofractionated radiation for prostate cancer is safe and very effective comes from
High Dose Rate Brachytherapy (HDR). With this form of radiation, the patient is brought to the operating room and hollow needles are implanted into the prostate. After the patient leaves the operating room (with the needles in place) one or several HDR treatments are given. With this treatment high doses of radiation are given in only a few treatments (
accelerated hypofractionation). There have been several reports in the literature with long follow-up when this technique is used alone or in combination with external beam that it is safe and very effective. In many ways Cyberknife mimics HDR.
What are results to date with Cyberknife for Prostate Cancer?
The Cyberknife was developed by a Neurosurgeon at Stanford. Stanford was the first academic institution to study the use of Cyberknife for prostate cancer. In their first report of under 50 patients with early prostate cancer they reported that it was safe, with very few side effects and no serious side effects. They also reported excellent cancer control with no recurrences. However, this was an early report from a single hospital and they treated patients with very favorable prostate cancer. More recently, the group from Stanford combined their data with a Cyberknife center in Naples Florida which confirmed their results with much longer follow-up and more patients. Twenty one Cyberknife centers in the United States are conducting a trial in which patients with early prostate cancer receive 5 treatments of accelerated hypofractionated treatment the same way the Stanford group treated their initial patients. To date over 320 patients have taken part in this study. Forty two patients are from the BIDMC's Keith Fields Cyberknife Center. The results on the first 250 patients has been reported. The rates of minor side effects has been low, acceptable and similar to what is observed with external beam (IMRT/IGRT). Cancer control rates also have been excellent, but more follow-up is needed to confirm these findings.
Who is treated with CybeKnife?
There are often many types of radiation that can be used to treat most stages of prostate cancer. These include, EBRT, brachytherapy and now Cyberknife . Many patients with early stage prostate cancer are candidates for Cyberknife therapy. This is a five Cyberknife treatment regimen. Patients with more advanced prostate cancer may be eligible for treatment with 5 weeks of external beam irradiation with two Cyberknife treatments. Even if you a candidate for Cyberknife to the prostate it may not be possible in all situation to do this form therapy. Although the Cyberknife device is approved by the Food and Drug Administration (FDA) to treat cancer anywhere in the body, many insurance companies consider Cyberknife "experimental" because the lack of published literature reporting
results. Therefore we have to make sure your insurance would cover this form of treatment prior proceeding with the treatment.