Cyberknife for Prostate Cancer
What is Cyberknife?
Cyberknife is a treatment using external beam radiation. It is the brand name of a machine that delivers stereotactic radiation therapy or "radiosurgery." Despite the name, Cyberknife does not involve a knife, cutting, or surgery for treatment. It uses a linear accelerator (a machine that makes radiation) on a robotic arm that allows the radiation beam to be delivered from thousands of directions. Cyberknife uses real-time image-guided radiotherapy (IGRT) in order to treat tumors in different parts of the body, including the prostate. What this means is that the motion of the tumor is tracked, and the radiation can be directed and delivered accurately based on the motion of the tumor.
What is Involved in Cyberknife Treatment?
You will see a urologist a week or two before treatment. This doctor will place gold markers, known as "fiducials", in your prostate as a way of marking the target. This is done under ultrasound guidance, similar to the procedure for prostate biopsy. The tumor position will be tracked during the Cyberknife treatment using the fiducials.
After the gold markers have been placed, a CT simulation is performed. During this CT scan, you will be positioned in the same way you will be positioned during the actual treatments. The physician uses this scan to outline the treatment area and organs or tissues to be avoided. This information is used to create the treatment plan.
The number of treatments (called fractions) and the amount of radiation (dose) per fraction can vary. Each fraction is a higher radiation dose than is used with traditional radiation, but fewer fractions are given. Typically, treatments include:
- Four or five fractions (treatments).
- Treatment is given over 1-2 weeks.
- The total dose in the mid to high 30 Gray range.
- Each treatment session is 30 to 90 minutes (larger tumors take longer to treat than smaller ones).
While you are being treated, the machine takes pictures of the tumor, which are compared in real-time to the images from the CT simulation. The CyberKnife robot moves around you to deliver precise treatment that can be adjusted as the prostate moves when you breathe.
Why Use Cyberknife for Prostate Cancer?
Cyberknife is a good option for prostate cancer because:
- Treatment is convenient and complete in fewer fractions – 5 compared to 44 fractions in traditional radiation.
- It spares more normal tissue.
- It is more accurate than traditional radiation.
- There are fewer side effects.
- Treatment is performed as an outpatient procedure.
In addition, prostate cancer is a slower-growing tumor. Because prostate cancer cells are growing slowly, they may be more sensitive to higher doses of radiation per fraction than other cancers. This means that delivering radiation in larger doses in fewer treatment sessions may improve outcomes.
Who is a Candidate for Treatment?
Cyberknife is typically used for patients with:
- Early-stage disease.
- Localized disease (confined to the prostate).
- A prostate volume (size) of less than 80-100 cm.
- A lesion or tumor that is untreatable by surgery or other radiation modalities.
Some people with enlarged prostates may be given hormone therapy to try to shrink the prostate to be able to get Cyberknife treatment. Patients who are considered high risk for spread to the lymph nodes or have cancer in the lymph nodes are not good candidates for Cyberknife.
What are the Possible Side Effects of Cyberknife?
Side effects are similar to those with conventional fractionated radiation therapy. The side effects include:
- Urinary irritation symptoms such as:
- Burning with urination.
- Rectal irritation.
- Erectile dysfunction.
These side effects are usually temporary.
Freeman D and King C. Stereotactic body radiotherapy for low-risk prostate cancer: five-year outcomes. Rad Onc 6:3, 2011.
Kilby, W., Dooley, J. R., Kuduvalli, G., Sayeh, S., & Maurer Jr, C. R. (2010). The CyberKnife® robotic radiosurgery system in 2010. Technology in cancer research & treatment, 9(5), 433-452.
King, C. R., Lehmann, J., Adler, J. R., & Hai, J. (2003). CyberKnife radiotherapy for localized prostate cancer: rationale and technical feasibility. Technology in cancer research & treatment, 2(1), 25-29.
Yoshioka Y, Nose T, Yoshida K, et al. High-Dose Rate Brachytherapy as Monotherapy for Localized Prostate Cancer: a Retrospective Analysis with Special Focus on Tolerance and Chronic Toxicity. Int J Rad Oncol Biol Phys 56: 213-220, 2003.