CyberKnife® Robotic Radiosurgery

"Most advances in cancer treatment are small steps forward, but occasionally there is a giant leap."


This article discusses a new and innovative radiosurgery technique, CyberKnife®, which is used to treat primary and secondary cancers, without the need for open surgery and long recovery periods. 

Contents

The CyberKnife® System is a robotic radiosurgery instrument that is revolutionising the way 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 and brain to include the rest of the body. He went on to found Accuray Incorporated, manufacturers of the CyberKnife® System. CyberKnife® is in clinical use throughout the world with over 60,000 patient treatments conducted. There are currently 3 units in the UK, and over 300 worldwide.

What is CyberKnife®?

The name “CyberKnife” is actually a bit of a misnomer, there are no knives in sight! However, it does allow the ablative treatment of tumours (hence “knife”) to be performed painlessly and effectively without the need for an operation by a robotic (hence “cyber”) linear accelerator (radiotherapy machine)

Conventional radiotherapy uses large field sizes and just a few radiation beams to treat ‘regions’ in the body, which means the dose given to the tumour is often limited by the radiation tolerance of the surrounding normal tissues. The latest chemotherapy and ‘magic bullet’ drugs have been a small step forward, but they have side effects and have generally not lived up to the hype.

Tumours are chaotic, and tend to wrap themselves around, or are close to other vital tissues. This means that the surgeon’s skills can be stretched to the limit, or the use of conventional radiotherapy would damage too much healthy tissue. Cancer radiation oncologists need a clear image of the exact location of the tumour (with all its irregularities) so that the delivery of radiation can be accurately pinpointed to these parts, and these parts alone. This is where CyberKnife® comes in. 

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. BMW originally created this robotic arm for manufacturing their cars. 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. CyberKnife® also achieves a fast dose gradient ('fall-off') at the edge of the tumour, minimising normal tissue dose.

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 advances enable the use of highly innovative and sophisticated planning and targeting software to treat tumours, the robot 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 tissues; CyberKnife® has changed this concept overnight with potentially 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  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?

The treatment is so accurate that it is now possible to treat tumours previously thought to be untreatable. Although the results of treatment do not always show immediately, in most cases the procedure will initially stop the growth of tumours before gradually reducing their size.

As there is no open surgery, the complications normally associated with an operation are eliminated, as is the need for a long recovery time. This makes treatment suitable for those who are not well enough to cope with the side-effects of surgery and most patients leave the clinic the same day as their treatment.

Major operations such as lung and liver resections, removal of pancreas and prostatectomy now have a viable alternative option with this technique.

Tumours in the body

Current indications include the treatment of stage 1 non-small cell lung cancer (as an alternative to surgery, or in patients with inoperable tumours, or who are medically inoperable), lung metastases, locally advanced pancreatic tumours, early prostate cancer, early kidney cancer, and treatment of primary or secondary liver tumours. This technology can also be used to retreat cancers that have recurred following conventional radiotherapy, for example head and neck or rectal cancers. These are situations that were previously untreatable using radiation. CyberKnife® is not usually appropriate for patients with widespread metastases or tumours over 8cm in diameter.

Tumours in the brain and spine

Within the brain CyberKnife® can be used for the same indications as Gamma Knife® including brain metastases (up to three), low grade astrocytomas, pituitary tumours, meningiomas, spinal tumours and trigeminal neuralgia. The use of 6-dimensional skull tracking makes this treatment IS at least as accurate as Gamma Knife® without the inconvenience of a frame bolted to the patient's skull. However, CyberKnife® is not usually appropriate for patients with widespread metastases.

Summary

As clinical oncologists, we are excited about this major leap in the application of the new technologies to treat cancer. In a way there is nothing particularly new as all of the theory has been in place for some time, but it is the ability to combine all the technologies into one unit that suddenly opens the door to a host of new treatment possibilities.

What happens before treatment?

Patients  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 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 early published data so far suggests that CyberKnife® is at least as effective as other forms of treatment in many indications, and very safe.

Who will provide my care?

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

How do I refer patients for CyberKnife®?

Treatments can take a few months to set up with insurers, and NHS ETA applications are also a lengthy process, so referrals need to come through as soon as possible after CyberKnife® has been discussed as a possible treatment option. Referrals arrive from a wide range of specialist surgeons and oncologists as well as directly from patients as the CyberKnife® is so versatile. Referrals can be made through the CyberKnife® centres or by contacting Andrew Gaya directly.

The future

The potential for this form of instrumentation is incredible, and the next few years will see some exciting new developments in cancer treatment. Trials are now well underway including a study of CyberKnife® compared with 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 the application of the therapy to correct electrical disturbances in the heart (as an alternative to catheter ablation). CyberKnife® is also being trialled in early breast cancer.

Continual software improvements and upgrades to the CyberKnife® System mean that as each year passes, fewer tumours require metallic markers to be inserted and so eventually CyberKnife® may be a 100% non-invasive treatment option. In my opinion CyberKnife® is currently the pinnacle of radiation treatment delivery and I am proud to be actively involved with this application and its use in caring for our patients.

For further information on the author of this article, Consultant Clinical Oncologist, Dr Andrew Gaya, please click here.
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