Muacevic_EU_Neuro.qxp 18/7/07 15:51 Page 32
Neurosurgery
Cyberknife Radiosurgery – A New Treatment Method for
Image-guided, Robotic, High-precision Radiosurgery
a report by
Alexander Muacevic and Berndt Wowra
European Cyberknife Center Munich
Cyberknife Radiosurgery – Overview Technology
Cyberknife technology is based on radiosurgical principles that have been The Cyberknife technology is a composition of two main parts: the
in clinical practice for 30 years. Radiosurgery is the precise application of a radiation source, which is a lightweight and compact photon device
high (tumour-destructing) dose of radiation in a precisely defined target (6 MeV linac, dose rate 4 Gy/minute) coupled with a robotic arm capable
volume, while protecting the surrounding healthy tissue. During of moving in six degrees of freedom (Kuka GmbH, Augsburg, Germany).
radiosurgery, many radiation beams from different directions intersect in The robot can achieve 1,200 positions during treatment. It is linked to a
the tumour region, where they accumulate. The surrounding healthy tissue computerised localisation system consisting of two X-ray generators that
receives only a small amount of the total dose. Until recently, the Gamma are fixed on the ceiling to enable orthogonal images of the target region.
Knife system was the standard instrument for neurosurgical applications, Images are recorded on silicon detectors that generate high-resolution
and some centres use linear accelerators (linacs) for clinical radiosurgical digital images. Depending on the location of the target region, exact
procedures. These systems, which are used mostly in conventional radiation patient positioning is enabled by a five-axis patient couch. During
oncology, have to be readjusted for every radiosurgical treatment. They treatment, the system automatically corrects patient movements in
must also undergo physical testing, because radiosurgical applications a range of 10 millimetres. A dedicated algorithm compensates for
demand significantly higher quality and precision requirements than the system’s inherent latency. For cerebral and spine indications,
conventional radio-oncological applications. However, Gamma Knife and co-registration of the acquired X-ray images of the bone structures with the
conventional linacs share the same necessity of applying an invasive digitally reconstructed images from the planning computed tomography
stereotactic ring on the patient’s head in order to achieve the desired (CT) – digitally reconstructed radiographs (DRRs) – is performed. DRRs are
accuracy of ±1mm. The revolutionary development of the Cyberknife matched with the X-ray images during treatment (see Figure 1).
technology, combining integrated image-guided and robotic technology,
has led to a paradigm shift in radiosurgery.
1,2
Dynamic Patient Correction
Moving target volumes can be monitored, and irradiation dynamically
Advantages of Cyberknife Radiosurgery adapts to the movement accordingly. After fiducial markers are applied
With Cyberknife technology, an invasive stereotactic head frame is no longer percutaneously, internal organ movement is defined by the X-ray image-
required in order to obtain the highest possible accuracy for brain guided system. Simultaneously, external light-emitting diodes, which are
treatments. Non-invasive and pain-free radiosurgical treatment is now fixed on the breast of the patient, measure the breath excursions. The
available to patients. In addition, if feasible, the treatment can be divided software calculates the organ movement, taking into account the internal
into several stages,
2
which makes it even safer to treat larger lesions or those and external target volume. Systemically performed X-ray image updates
in highly sensitive areas. Apart from standard neurosurgical indications (i.e. are the basis for iterative corrections of the correlation model.
5,6
acoustic neurinomas, meningeomas, brain metastases), radiosurgical
applications are currently evolving to include extracranial indications. It is Frameless Stereotaxy – Accuracy
now possible to treat tumours of the spine, pancreas, lung and liver safely Academic studies at the European Cyberknife Center Munich, Germany,
and effectively with radiosurgical techniques in cases where the tumours are and Stanford University, US, have shown that frameless Cyberknife
well delineated from the surrounding healthy tissue. In selected cases, this technology is as precise as the conventional frame-based systems.
could replace a surgical procedure. Because of the physiological breath- Phantom studies achieved total accuracy results (including imaging,
dependent organ movement, until now it has not been possible to apply planning and treatment) of 0.42±0.4mm.
3,4
high-radiation doses to body lesions. The newest development in Cyberknife
radiosurgery is a breath-triggered realtime movement-correction system, Treatment Schedule
which makes it possible to apply radiosurgical doses to these lesions. The An individual head mask is used for brain treatments. This helps to stabilise
Cyberknife moves according to the tumour’s movement. Infrared cameras the patient’s head during treatment. For lesions in moving organs such as the
follow the breath excursions and send information online to a robot, which lung, liver and pancreas, small (5mm) metal markers are implanted
steers the linac into position.
6
Anaesthesia or dedicated body stereotactic percutaneously in the vicinity of the lesion. They are used as landmarks for
frames, as used with conventional radiation devices to suppress respiration, image registration and are detected automatically by the X-ray camera
are no longer necessary. Cyberknife treatment is designed for outpatient system. Image registration for brain treatments is performed without external
treatment, which significantly enhances the quality of life of cancer patients. fiducials and uses bony scull structures. All treatments are performed on the
A hospital stay or rehabilitation is not needed in most cases. Treatment time basis of CT and magnetic resonance imaging. The frameless technology
is dependent on tumour location and size and the organs at risk. A full allows the planning of images days before radiation application. Dose
course of radiosurgery lasts between 60 and 90 minutes. planning is performed using an inverse dose planning algorithm whereby the
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