CyberKnife robotic radiation treatment machineCyberKnife is a type of robotic radiation therapy machine.  It is different from normal radiation machines in the following ways:

  1. The machine continuously tracks the location of the marker seeds in the prostate gland during the treatment session.  If the prostate moves, the radiation beam moves.
  2. CyberKnife can only treat small areas.  The prostate gland is small enough for this treatment.  However, cyberknife is not able to treat larger areas like the lymph gland chains in the pelvis.
  3. CyberKnife requires only 5 treatments, and gives a very high dose each treatment.  It more or less indiscriminately damages everything in its target zone, hence the “knife” name.  Cyberknife  is a form of radiosurgery.  Radiosurgery was originally invented to destroy small brain tumors without having to open up the skull.

Normal radiation therapy machines are more versatile.  They can treat larger areas, for instance they can treat massive prostate glands and can they include areas outside the prostate such as the lymph nodes in the pelvis if desired.  The radiation therapy can be given at a traditional slow daily rate over many days which gives the healthy tissues a chance to heal themselves.

The robotic tracking of the marker seeds is an impressive feature.   With CyberKnife, because potentially destructive high daily doses are used, the robotic tracking is required to ensure that the rectum or bladder do not move into the target zone.

The shorter treatment duration of CyberKnife is very enticing.  It is a newer technology, so there has not been much long term results published yet.  However, the daily radiation treatment dosages are similar to the ones that we have used with HDR brachytherapy.  Dr. Katz has published 7 year results for CyberKnife.  The chance of being free from cancer recurrence at the 7-year mark was 96% for low-risk prostate cancer, and 89% for intermediate risk prostate cancer.   There were very few serious long term urinary or rectal side effects.  67% remained sexually potent.


  1. Cyberknife uses 5 high dose treatments that kill both cancerous cells and healthy cells within the target zone.
  2. Because of this, treatments must be highly targeted to a small area.
  3. There are not many clinical results available yet.

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