This article, by a Senior Oncologist, outlines the revolutionary new cancer treatment CyberKnife®. Find out what can be treated with this new form of radiosurgery and how CyberKnife® works.
Contents
- Why cancer has been difficult
- Radiosurgery
- How CyberKnife® works
- Combining imaging with treatment
- Image Guided Therapy
- Cyber Seek and Destroy
- What can CyberKnife® treat?
- When other treatments have failed
- Summary
Why cancer has been difficult
Cancers can arise from any cell in the body and therefore can take any form. When cancer forms a single solid tumour or mass, surgery can be straightforward, but what about when the cancer grows around other essential tissues and organs – especially in the head and neck? Many tumours, particularly of the head and neck have previously been effectively inoperable, and so major changes in treatment approach were needed. There are targeted drugs which are designed as ‘magic bullets’ or conventional chemotherapy, but these can have variable success as well as serious side-effects. There is photodynamic therapy (PDT), but this can only work on surface tumours, such as the tongue or throat. There is conventional radiotherapy, but this again is often too inaccurate and damages surrounding tissue. In these circumstances the ideal is to map the precise location of the tumour and to then apply an appropriate level of irradiation specifically to that area – and no other area. This approach is called conformal radiotherapy. Highly focussed radiation techniques are now available where high radiation doses can be applied with minimal damage to surrounding tissues.
Radiosurgery
If tumours only occurred in convenient locations the job of the surgeon and oncologist would be made so much easier. The trouble is that they don’t and many wrap themselves around or are close to other vital tissues or they spread into delicate areas such as nervous tissue. This means that the surgeon’s skills can be stretched to the limit or that the use of conventional radiotherapy would also damage too much healthy tissue. What is needed is a clear image of the precise 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® can come in. CyberKnife® is an example of a ‘stereotactic radiosurgical technique’ and combines the benefits of controlled irradiation with on-line tumour imaging and tracking.
How CyberKnife® works
The vast array of different angles/trajectories from which pencil beams of radiation converge upon the tumour lead to an extremely high cumulative dose of radiation therapy at the convergence point (the target/tumour) and yet a very fast 'fall-off' of dose at the periphery of the carefully mapped target. The surrounding normal tissues/organs only receive a small fraction of the high central dose of therapy.
Whilst any tumour may be destroyed by a very high dose of radiation therapy, it has very often been the case, with orthodox radiotherapy, that it has not been possible to deposit the required dose on a tumour without also depositing a dangerously high dose of radiation on the surrounding organs. CyberKnife® can overcome this problem by its capability to so accurately target and achieve a fast dose gradient ('fall-off') at the perimeter of the tumour/target.
Combining imaging with treatment
Medical imaging and in particular ‘volumetric’ imaging – such as CT and MRI have advanced so far that it is now possible to visualise and locate the exact positioning of the tumour. The trick is to match the surgery (or in this case irradiation) to that precise location.
Image Guided Therapy
In other words the CyberKnife® can for all intents and purposes see where the tumour is and has the ability to treat only the affected areas. It has taken conventional design and configuration and developed these to provide the state of the art in image guided radiotherapy system. Designed for radiosurgical applications, the CyberKnife® is ideally suitable to deliver highly conformal treatments and its use for many tumour sites is being increasingly reported. The ability to provide highly conformal treatments and verification in an integrated medical appliance is a highly desirable combination.
The name CyberKnife, is actually a bit of a misnomer depending on your definition of ‘knife’. However, it does allow the treatment of tumours to be performed painlessly and effectively without the need for an operation.
Cyber Seek and Destroy
A further important feature of the CyberKnife® is that the robotic arm can not only track the tumour's position, but it also detects any movement of either the tumour or the patient, and automatically corrects its positioning. Its ‘intelligent’ unit can therefore allow for movements such as breathing or other movements while targeting the tumour. This means that there is no need to be fitted with an invasive brace or restraining device during the treatment phase, making the whole procedure less difficult for the patient.
The robotic radiotherapy arm can deliver multiple beams of high-energy radiation that destroys abnormal tissue without damaging surrounding areas. 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.
What can CyberKnife® treat?
CyberKnife® can be used to treat the following types of cancer:
In many cases, stereotactic radiosurgical techniques (including Gamma Knife®) are the preferred treatment option now for treating the following brain cancers:
- Arteriovenous malformations (AVMs)
- Other vascular anomalies including cavernoma, haemangioblastoma and glomus tumour,
- Meningiomas
- Acoustic neuromas
- Brain metastatic disease (i.e. spread of cancer from other sites in the body to the brain)
- Brain tumours that are too deep in the brain for orthodox surgery
NB: CyberKnife® is not appropriate for AVM, glioblastoma (stage 4 astrocytoma), meningiomas over 5cm in diameter, or brain metastases greater than three in number.
Many of the vascular problems that occur in the brain also occur in the spine and CyberKnife® has marked advantages over other radiosurgical techniques in that it is capable of targeting spinal lesions. Also, vertebral tumours (the vertebra is the spine bone) may similarly be treated by this technology (with sparing of the radiosensitive spinal cord that runs through the vertebra).
Single or several tumours in the lung.
Individual lung cancers (typically stage 1 non-small cell).
CyberKnife® now offers a new radiotherapeutic method with potential to cure early prostate cancer with far fewer visits to the radiotherapy department for therapy.
The pancreas is surrounded by delicate and radiosensitive structures such as the duodenum and a sophisticated deposition of dose is required to allow maximal deposition of radiation dose on the pancreatic tumour and yet sparing of these surrounding organs.
Quite simply, CyberKnife® seems the important advance that we have been waiting for, and more than one lesion can be targeted. This is suitable for liver metastases and primary liver cancer or hepatocellular carcinoma.
Renal cancer is recognised as being one of the more radioresistant cancers and the need for higher dose therapy is restricted by the dose that surrounding tissues will tolerate. Focused radiation therapy by CyberKnife® can be most useful in early kidney cancer.
When other treatments have failed
The ability of CyberKnife® to focally deposit high doses of ablative radiation on discrete sites of cancer has led to the safer re-treatment of cancers that may have re-grown after previous radiotherapy - as the surrounding normal tissues (almost at tolerance dose to radiation exposure) is spared much of the re-treatment dose.
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.
For further information on the author of this article, Consultant Clinical Oncologist, Dr Chris Nutting, please click here.
An AVM or arteriovenous malformation forms when arteries connect directly to veins. This direct connection forms a high-pressure shunt or fistula. The veins are not able to handle the pressure of the blood coming directly from the arteries. The veins stretch and enlarge to create a “nidus”. Usually there are multiple feeding vessels in an AVM and many draining veins.
Full medical glossaryAn AVM or arteriovenous malformation forms when arteries connect directly to veins. This direct connection forms a high-pressure shunt or fistula. The veins are not able to handle the pressure of the blood coming directly from the arteries. The veins stretch and enlarge to create a “nidus”. Usually there are multiple feeding vessels in an AVM and many draining veins.
Full medical glossary
