How Does the CyberKnife System Treat Prostate Cancer?

The challenge that doctors face in treating prostate tumors with radiation therapy is that the prostate moves unpredictably as air passes through the rectum and as the bladder empties and fills. Minimizing any large movements of the prostate can help reduce unnecessary irradiation of surrounding healthy tissue. The CyberKnife Robotic Radiosurgery System is able to overcome this challenge by continuously identifying the exact location of the prostate and making active corrections for any movement of the prostate throughout the course of the treatment. During treatment, a patient lays still and breathes normally while the CyberKnife zeroes in on a moving target – the prostate – and irradiates it without harming surrounding areas. As a result, the procedure is more comfortable for patients, radiation is delivered more accurately and treatments can be completed in four to five days.

Currently the CyberKnife Radiosurgery System is most frequently used by itself for patients with early stage prostate cancer confined to the prostate or in combination with another therapy, such as external beam radiation for patients with disease that extends beyond the prostate. Depending on the stage of the patient’s prostate cancer the doctor will recommend a treatment plan.

Over a dozen clinical experiences have been published to date on CyberKnife prostate SBRT. At 5 years after treatment a recurrence-free rate of 93% has been reported [45]. Recurrence-free rates of 100% at 44 months [46], 97.5% at 51 months [47], and 94% at 4 years [48] have also been reported. Toxicity has been quite low; rates of grade 2-3 toxicity at 20-60 months after treatment range from 2-10% for urinary toxicity and 0-5% for bowel toxicity [45-52]. Erectile dysfunction has ranged from 60% at 35 months for an early experience [53] to 13-40% at 1.5-3 years for more recent experiences in which the prostate gland is delineated with the aid of MRI [49, 50, 54], which typically reduces the volume of the region exposed to radiation [55].

What does a typical CyberKnife treatment entail?
Prostate cancer treatment with the CyberKnife System involves a team approach, in which several specialists participate. A team may include:

• a urologist
• a radiation oncologist
• a medical physicist
• a radiation therapist 
• medical support staff

Once the team is in place, the patient will begin preparations for CyberKnife treatment. As part of their diagnosis, doctors will have measured prostate specific antigen (PSA) levels via a blood test that will be used to help track treatment results. Prior to CyberKnife treatment, patients will be scheduled for a short outpatient procedure in which three to five tiny gold seeds – called fiducial markers – are inserted into the prostate. The fiducials are placed through a needle, which is guided via an ultrasound. Patients may be asked to clean out their rectum with an enema the day of the fiducial placement.

The CyberKnife System uses the fiducials as reference points to identify the exact location of the prostate. Doctors will wait approximately one week after insertion of the fiducials before CyberKnife treatment planning can begin to ensure that fiducial movement has stabilized.

Prior to the treatment, a special custom-fit body cradle will be made. The cradle is made of a soft material that molds to the patient’s body, ensuring that the patient is in the same position for each treatment session and is comfortable during the procedure.

While lying in the cradle, patients will undergo a CT scan. This CT data will be used by the CyberKnife team to determine the exact size, shape and location of the prostate. An MRI scan also may be necessary to fully visualize the prostate and nearby anatomy. Once the imaging is done, the body cradle will be stored and used during CyberKnife treatment.

A treatment plan will be specifically designed by a medical physicist in conjunction with the patient’s doctors. Patients will not need to be present at this time. During treatment planning, CT and/or MRI data will be downloaded into the CyberKnife System’s treatment planning software. The medical team will determine the size of the area being targeted by radiation and the radiation dose, as well as identifying critical structures – such as the bladder and rectum – where radiation should be minimized.

At this time, the CyberKnife System will be able to calculate the optimal radiation delivery plan to treat the prostate. Each patient’s unique treatment plan will take full advantage of the CyberKnife System’s extreme maneuverability, allowing for a safe and accurate prostate cancer treatment. After the treatment plan is developed, patients return to the CyberKnife center for treatment. The treatment is usually delivered in one to five sessions.

For most patients, the CyberKnife treatment is a completely pain-free experience. They may dress comfortably in street clothes, and the CyberKnife center may allow patients to bring music to listen to during the treatment. Patients also may want to bring something to read or listen to during any waiting time, and have a friend or family member with them to provide support before and after treatment.

When it is time for treatment, patients will lay on their custom body cradle. The radiation therapist will ensure the body cradle is properly adjusted and that patients are appropriately positioned on the treatment couch. When patients are ready for treatment to begin, the location of the prostate will be tracked and detected. The medical team will be watching patients every step of the way as the CyberKnife tracks the patient’s prostate as it moves, and safely and precisely delivering radiation to it.

The CyberKnife System’s computer-controlled robot will move around the patient’s body to various locations from which it will deliver radiation. At each position, the robot will stop. Then, special software will determine precisely where the radiation should be delivered. Nothing will be required of the patient during the treatment, except to relax and lay as still as possible.

Once prostate cancer treatment is complete, most patients quickly return to their daily routines with little interruption to their normal activities. If treatment is being delivered in stages, patients will need to return for additional treatments over the next several days as determined by their doctors.

Occasionally patients report temporary symptoms following treatment, which may include reduced urinary stream, burning with urination, more frequent urination, increase in frequency of stools, loose stools and more gas with bowel movements than usual. To date, prostate cancer patients have experienced low rates of moderate to severe toxicity ranging from 0-3.5% for urinary and 0-2% bowel toxicity [45-52]. Doctors will discuss all possible side effects with their patients prior to treatment. In addition, doctors may prescribe medication to control any side effects, should they occur.

After completing a CyberKnife radiosurgery treatment, it is important for patients to schedule and attend any follow-up appointments. Response to prostate cancer treatment varies from patient to patient. Clinical experience today examining treatment outcomes up to 5 years following treatment has shown that most patients respond very well to CyberKnife treatments. CyberKnife physicians will monitor the outcome in the months and years following a patient’s treatment using PSA tests and digital rectal exams.