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Know the Cyberknife

The Cyberknife is a breakthrough product that expands the potential of precision radio surgery to every part of the body

Dr Sanjay Chandrasekhar The writer is Senior Consultant Oncologist Apollo Speciality Hospital Chennai

The Cyberknife is the world's first and only system which can treat tumors, ensuring a sub-millimetre accuracy and also the only system available today to treat tumours in any part of the body with the same precision

Radiation oncology is amidst a period of rapid technological change. Advancements in imaging modalities, computerised treatment planning and radiation delivery now enable unprecedented sophistication in radiotherapy. These advancements have enhanced the quality of treatment through better target delineation, dose delivery and normal tissue sparing. Modern imaging techniques have been a key element of this technological progress. The array of radiation therapy techniques implementing these modern imaging approaches has been termed Image Guided Radio Therapy (IGRT). Computerised treatment planning software have integrated CT, MRI and PET scans. It is now possible to visualise the target volume on three different scans.

Target delineation and contouring can be accomplished on all three scans and the software has the capability of fusing all three scans. This has led to enhanced accuracy in target volume contouring. In currently available IGRT systems, imaging before and during treatment, helps in adjusting for target motion or the patient's positional uncertainty. Thus, without accurate targeting, one is, at least figuratively practicing in the dark. Target identification itself, however, can be a 'moving target.' A key feature of IGRT is the facilitation of four dimensional (4D) target localisation. Reproducibly positioning the patient is an important element of fractionated RT delivery. However, both systematic and stochastic errors in patient set-up contribute to variation in daily positioning. Reproducibility is also hindered by movement or changes occurring in target and normal tissues between (inter-fraction) or even during (intra-fraction) treatment. IGRT has to a large extent eliminated these problems and has incorporated strategies to more accurately localise the target. This has led to more effective and less toxic therapy.

Breakthrough Invention

The cyberknife is a breakthrough product that expands the potential of precision radio surgery to every part of the body. Cyberknife treatment is a painless outpatient procedure that involves no stereotactic frame being fixed to the skull or body. There is no blood loss either. Both the benefits are highly desired by patients who receive these treatments. (See box)

Linear Accelerator V/s Cyberknife

So what is it that sets the cyberknife aside from the conventional linear accelerator? Linear accelerator (Linac) has undergone many changes over the last four decades or so. Currently, available Linacs apart from being able to produce multiple energy X-ray and electron beams also possess Multi Leaf Collimators (MLC) and Micro Multi Leaf Collimators (mMLC) which help in shaping the X-ray beam to conform to the shape of the tumour, thereby sparing normal tissues from unnecessary radiation. These collimators have also played a role in Intensity Modulated Radiotherapy (IMRT) where dose intensification and dose modulation is possible as the X-ray beam passes through the body. This results in delivering high doses to the tumour and reducing doses to normal tissues which come in the path of the X-ray beam.

Now you have Rapid Arc technology which reduces the treatment time of one sitting. hybrid systems have also been developed now. These linear Accelerators incorporate advanced imaging techniques within the therapy machine. However, one has to understand the limitations of this series of equipment. During every sitting of radiation, the Linac acquires an image through an in-built CT scanner. This image is fused with a pre-treatment reference image. When the matching of fusion nears perfection, the machine goes into the 'On' mode. The catch here is that one has to assume that the target is not moving during the treatment session. This is where the Cyberknife's intelligent robotics comes into play. The image acquisition is also very sophisticated. The Cyberknife is able to track even a moving tumour and deliver radiation from many angles. Conventional Linacs have a limit to the number of gantry angles from which radiation can be delivered. The Cyberknife has no limit whatsoever. A single treatment session may, for example, use even 100 to 200 beams to treat a tumour. All this is accomplished without the need for a frame to be fixed and most treatments are completed in one to five sittings.

Futuristic Technology

The Cyberknife uses technology that is truly futuristic. With it we have now entered a new frontier in cancer treatment as well as in the treatment of certain benign tumours and functional radiosurgery. Collectively, all these treatments fall into a new field of radiotherapy called Stereotactic Body Radiotherapy (SBRT) hitherto not possible with existing radiation equipment.

SBRT can now be offered as a viable alternative to surgery in the following clinical situations:

• Primary Liver Cancer (Hepatocellular carcinoma or HCC): The two major reasons for considering SBRT for liver cancer is that underlying severe liver disease often renders patients medically inoperable and that other non-surgical therapies have generally achieved rather modest success in that setting.
• Lung Cancer: SBRT can be used for stage I medically in-operable non-small cell lung cancer. SBRT is also proving to be a very valuable tool in the treatment of solitary lung metastasis (secondaries) and rarely even in the case of multiple lesions in the lung.
• Spine: SBRT offers hope for patients with malignant spinal and para-spinal tumours, both primary and metastatic. It is an excellent treatment option for patients with benign spinal tumours such as schwanommas, neurofibromas and meningiomas.

SBRT is also being practiced as a treatment for prostate cancer, renal cell carcinoma of the kidney and for pancreatic cancers.

• Functional Radiosurgery: The most widely used functional application of Cyberknife radiosurgery is in the management of typical trigeminal neuralgia refractory to medical therapy. Approximately 50 per cent of typical trigeminal neuralgia patients remain pain free and off medication five years following radiosurgery.
• Vascular Malformations (AVM's): Cyberknife radiosurgery can dramatically reduce the risk of haemorrhage (bleeding). Radiosurgery obliterates the AVM nidus in more than 75 per cent of patients within three years of the procedure.
• Benign tumours in the Brain: CK radiosurgery can be used to treat acoustic neuromas, cranial nerve schwanommas, meningiomas, pituitary adenomas and craniopharyngiomas.
• Metastases (Secondaries) in the Brain: Cyberknife radiosurgery offers hope, especially in patients with a solitary tumour in the brain as well as for multiple secondaries in the brain.
• Glioblastomas: CK Radiosurgery appears to be a reasonable option for small, well circumscribed, high grade gliomas that recur after prior conventional large field radiotherapy and chemotherapy.

How is it Different?

So, how is the Cyberknife system different from other radiation delivery systems available today? Apart from the fact that no stereotactic frame is required to be fixed on the patient, breath holding which is difficult for some patients has also been dispensed with. In effect, even if the target moves with breathing, this machine tracks, detects and delivers radiation from many angles due to its maneuverability and versatility. The combination of image guidance cameras and the latest computer technology ensures that the Cyberknife System is able to overcome the limitations of older frame-based radiosurgery systems such as the gamma knife And Linac based X-knife.

A few words about the synchrony system are a must. This is the first technology in the world capable of delivering radiosurgery to tumours affected by the respiratory cycle. It uses a complex system of cameras, motion tracking software, fibre-optic sensing technology, infra-red emitters and a special tight fitting elastic patient garment.

A word about the X-Sight spine tracking system. This technology which is now part of most Cyberknife systems has enabled tracking of the spinal column without the need for fiducial markers to be implanted into the vertebrae.

So, we are entering into a new frontier in radiation therapy. The future is here now.

The writer is Senior Consultant Oncologist Apollo Speciality Hospital Chennai
canray@hotmail.com