CyberKnife® FAQs

This article by Harley Street Cyberknife® Expert, Dr Andrew Gaya, explains the new radiosurgery technique and  answers questions such as "Who is suitable for CyberKnife?" and "How does CyberKnife work?".



The CyberKnife® System is a robotic radiosurgery instrument that is revolutionising the way some cancers are treated. It was developed by John Adler, a neurosurgeon from Stanford University in the 1990’s as a way of extending radiosurgery from the head to include the rest of the body. CyberKnife is in clinical use throughout the world with over 100,000 patient treatments conducted. 

What is CyberKnife®?

Conventional radiotherapy uses large field sizes and just a few radiation beams to treat ‘regions’ in the body which means that the dose given to the tumour is often limited by the radiation tolerance of surrounding normal tissues. The CyberKnife® system is completely different as it uses hundreds of pencil thin beams and thousands of potential treatment angles to target individual tumours. The machine consists of a highly manoeuvrable miniaturised linear accelerator (a machine that delivers high energy x-rays) attached to a robotic arm. This robotic arm is complimented by a state-of-the-art targeting system which pinpoints tumours with sub-millimetre accuracy and then fires in hundreds of high dose pencil-thin beams of radiation.

What makes CyberKnife® so special?

It is a very accurate form of radiation treatment that can be used as an alternative to surgery in many cases. The key is delivering the right dose to the right place at the right time whilst minimising damaging effects on normal tissue. I like to think of it as “precision without incision”. Technology advancements enable the use of highly innovative and sophisticated planning and targeting software to treat tumours, even moving up and down to track the target as the patient breathes, minimising any radiation dose to normal tissues. Theoretically any tumour target can be cured with radiation therapy, historically this has been limited by the tolerance of surrounding normal tissue; CyberKnife® has changed this concept overnight with obliterative doses of radiation delivered rapidly and with absolute precision. In radiotherapists’ terminology it combines extreme hypo fractionation (where radiation is given in larger doses or ‘fractions’ and in less sessions than traditional radiation therapy) with intrafraction Image Guided Radiotherapy (IGRT) and extreme Intensity Modulated Radiotherapy (IMRT) to produce a near-perfect dose distribution of radiation around the target, with minimal dose to surrounding healthy tissue. This enables the very high doses used to be given with absolute safety and confidence.

What can CyberKnife® treat?

Patients who were previously untreatable may now have hope. The CyberKnife® System can treat tumours all over the body and not just the brain as per some older machines. What makes it unique is that it can be used as an alternative to invasive conventional surgery in many cases.

What happens before treatment?

Patients will have a CT planning scan in order for the clinical oncologist, radiologist and physicist to determine the correct treatment volume, organs at risk, and radiation dose distribution. This scan can be fused with other imaging modalities such as MRI, PET scans and 3D angiography. Some tumours require the implantation of metallic markers, the size of a grain of rice (called fiducial markers), which help the software track the tumour more accurately. This can usually be done under local anaesthetic, one week before treatment. The treatment is explained in detail to each patient at a dedicated consultation, where discussions of any possible side effects will also take place. Due to the accuracy of targeting there have been very few serious side effects.

How long do treatment sessions last?

Treatments can last about an hour, are completely painless and usually non invasive. Most patients will have up to five treatments in contrast to conventional radiotherapy which involves up to 40 treatments, although there is now increasing use of single fractions with CyberKnife®.

Does it work?

CyberKnife® is a new technology, so there is currently a lack of large randomised clinical trials. The published data so far suggests that CyberKnife® is at least as effective as other forms of treatment in many indications, and very safe. Further trials are being set up or are ongoing.

Who will provide my care?

All patients being considered for CyberKnife® will have their care planned with a multidisciplinary team made up of specialised clinical oncologists, surgeons, radiographers and radiologists. 

What training was necessary?

The treating team were trained by Accuray and have spent time observing and then supervising and delivering treatment on other CyberKnife® machines in the UK and abroad. They have also attended conferences and symposia to obtain the very latest treatment data. The Clinical Oncologists have to complete additional training as CyberKnife® planning and treatment delivery is so different to conventional radiotherapy.

The future

The next few years will see some exciting developments in cancer treatment. Phase 3 trials are now underway including a study of CyberKnife® against conventional surgery for stage 1 or 2 lung cancer. CyberKnife® is being tested in functional brain disorders such as epilepsy and Parkinsons disease, and there are plans to extend it to correct electrical disturbances in the heart (alternative to catheter ablation). Continual software improvements and upgrades to the CyberKnife® System mean that as each year passes, fewer tumours require metallic markers to be inserted and that eventually CyberKnife® may be 100% non-invasive.

Suitable for CyberKnife®

  • Localised primary brain tumours (not glioblastoma)
  • Brain metastases (usually 1 – 3) if disease outside brain well controlled
  • Spinal tumours (primary, or secondary if localised)
  • Spinal metastases
  • Pituitary tumours
  • Trigeminal neuralgia
  • Stage I non small cell lung cancer
  • Liver or Lung metastases (less than 6 metastases in total usually, and there should be a plan to deal with them all)
  • Primary liver tumours
  • Isolated lymph node metastases
  • Locally advanced Pancreatic Cancer
  • Early Prostate Cancer (one of many options for treatment)
  • Recurrent head and neck cancers
  • Early Kidney Cancer

Not Suitable for CyberKnife®

  • Very large tumours (greater than 8cm in diameter)
  • Widespread metastatic disease
  • Glioblastoma (grade 4 astrocytoma)
  • Large meningiomas (of over 5cm in diameter)
  • Multiple brain metastases (usually greater than three)
  • Lung Cancer stages 2/3
  • Advanced or high risk Prostate Cancer
  • Oesophageal Cancer
For further information on the author of this article, Consultant Clinical Oncologist, Dr Andrew Gaya, please click here.
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