CyberKnife Radiosurgery for Brain Metastases
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Classic radiosurgery is a neurosurgical treatment concept for single-fraction irradiation of cerebral lesions not amenable to open surgery. Until recently it has been realized mainly by frame-based technologies (Gamma Knife; stereotactic linear accelerators). The CyberKnife described in 1997 is an image-guided frameless robotic technology for whole-body radiosurgery. It can be used for classic single-fraction radiosurgery and for hypofractionated treatments. The CyberKnife treatment procedure is completely non-invasive and can be repeated throughout the body if necessary. Brain metastases are an important and frequently treated indication of modern radiosurgery. Data concerning radiosurgical treatment of brain metastases with the CyberKnife are reviewed. Scientific evidence shows that the full-body applicability of the CyberKnife is not at the expense of an inferior intracranial treatment quality when compared to standard frame-based technology. The clinical results of CyberKnife single-fraction radiosurgery are in line with the published literature. The attractive therapeutic profile of CyberKnife radiosurgery is reflected by a high tumor control and a low toxicity and the repeatability of the treatments for recurrent metastases. Although hypofractionated treatments (in 3–5 fractions) of brain metastases have been performed with the CyberKnife to treat large metastases, the clinical significance of this new radiosurgical concept is unclear and requires further study. A new approach is to treat the resection cavity with radiosurgery after surgical removal of brain metastases. In this concept radiosurgery replaces fractionated radiation therapy as an adjunct to surgery. The initial results are very promising. The CyberKnife has been established as a modern non-invasive technology for intra- and extracranial radiosurgery. It adds to the oncological armamentarium and confers upon radiosurgery a greater emphasis as an oncological treatment concept.Keywords:
Cyberknife
Although the value of stereotactic radiosurgery for the treatment of brain tumours in children is well recognized, the widespread use of stereotactic radiosurgery in paediatrics has been limited by difficulties with rigid fixation for young children, the need for general anaesthesia, and certain characteristics of some paediatric brain tumors which may promote the risk of radionecrosis. The CyberKnife radiosurgery system is both frameless and precise and therefore offers potential solutions to these problems. We review the advantages of frameless radiosurgery for paediatric patients, discuss factors specific to CyberKnife stereotactic radiosurgery for children, and report our preliminary experience with a group of 21 patients.
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Classic radiosurgery is a neurosurgical treatment concept for single-fraction irradiation of cerebral lesions not amenable to open surgery. Until recently it has been realized mainly by frame-based technologies (Gamma Knife; stereotactic linear accelerators). The CyberKnife described in 1997 is an image-guided frameless robotic technology for whole-body radiosurgery. It can be used for classic single-fraction radiosurgery and for hypofractionated treatments. The CyberKnife treatment procedure is completely non-invasive and can be repeated throughout the body if necessary. Brain metastases are an important and frequently treated indication of modern radiosurgery. Data concerning radiosurgical treatment of brain metastases with the CyberKnife are reviewed. Scientific evidence shows that the full-body applicability of the CyberKnife is not at the expense of an inferior intracranial treatment quality when compared to standard frame-based technology. The clinical results of CyberKnife single-fraction radiosurgery are in line with the published literature. The attractive therapeutic profile of CyberKnife radiosurgery is reflected by a high tumor control and a low toxicity and the repeatability of the treatments for recurrent metastases. Although hypofractionated treatments (in 3–5 fractions) of brain metastases have been performed with the CyberKnife to treat large metastases, the clinical significance of this new radiosurgical concept is unclear and requires further study. A new approach is to treat the resection cavity with radiosurgery after surgical removal of brain metastases. In this concept radiosurgery replaces fractionated radiation therapy as an adjunct to surgery. The initial results are very promising. The CyberKnife has been established as a modern non-invasive technology for intra- and extracranial radiosurgery. It adds to the oncological armamentarium and confers upon radiosurgery a greater emphasis as an oncological treatment concept.
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Purpose: Compare the dose-distributions from two different radiation-delivery systems in the treatment of patients with lung and spinal metastases. Method and Materials: Patients with metastases underwent Cyberknife treatment at Seattle CyberKnife Center (SCC) since February 2006. Seven CT-image sets from SCC including the contours, and dose-matrix were imported through DICOM-RT into the Pinnacle treatment-planning system at MDACC for the purposes of creating an IMRT treatment-plan for the LINAC. Volumes of eight lesions ranging from 0.24- to 64.11-cc were used in this study. The treatment fractional sizes are 1-, 2-, 4- or 5-fractions and the prescription-dose per fraction is varied from 500- to 1600-cGy. The maximum dose of each plan was equal to 100%. Dose-volume histograms were generated for both CyberKnife and LINAC treatment. Results: Based on the dose-volume histograms, the percentage of the tumor-volume that received the prescription-dose varied from 84.8% to 100% for CyberKnife and from 90.1% to 100% for LINAC. The dose-heterogeneity within the tumor-volume received the prescription-dose that ranged from 31.6% to 63.9% with the mean of 43.2% for CyberKnife and from 14.4% to 31.6% with the mean of 25.2% for LINAC. Dose-conformality to the tumor-volume is comparable between CyberKnife and LINAC plans, but the CyberKnife has a slight edge for treating a small lesion (0.24 cc) with the critical structure located very closely to it. In general, the IMRT plans are better at sparing the surrounding critical structures than the CyberKnife plans. This was attributed to the exclusive use of anterior oblique beam-arrangement of CyberKnife. The dose comparison for the organs at risk will be presented. Conclusion: Dose-conformality is comparable between Cyberknife and LINAC plans. Dose-heterogeneity is greater for patients receiving Cyberknife treatment compared to LINAC. The use of anterior beam-arrangements in CybeKnife may increase integral-dose to anterior organs at risk compared to LINAC delivery systems.
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Purpose: To compare Extracranial Radiosurgery dose distributions to step and shoot Intensity Modulated Radiation Therapy (IMRT) aimed to the same dose prescriptions and constraints. Method and Materials: 12 patients treated by means of the Cyberknife system for extracranial tumors (7 lung, 2 pancreas, 2 liver and 1 prostate) were selected. Volume of the PTV ranged from 19.0 cc to 584.4 cc. The prescribed doses were 16–27 Gy to the 80% isodose surface in 1–3 fractions. IMRT treatment plans were calculated to obtain the same coverage of the PTV with same constraints to organs at risk. A 5-coplanar fields, step-and-shoot technique was employed with a 6MV accelerator. IMRT plans were generated by means of the Pinnacle treatment planning system. We compared homogeneity and conformity indexes and ratios between isodose volumes. Furthermore, a recently proposed index for comparison of radiosurgery plans was calculated. The new index balances conformity and steepness of the gradient outside the PTV. Results: Homogeneity index ranged from 1.35 to 2.00 (mean 1.54) for the Cyberknife and from 1.10 to 1.64 (mean 1.26) for IMRT. Conformity index ranged from 0.76 to 1.28 for the Cyberknife and from 0.79 to 2.55 for IMRT; the mean deviation of the conformity index from 1 was 0.14 and 0.74, respectively. The ratio between 20% and 80% isodose volumes ranged from 4.0 to 28.0 (mean 12.9) for the Cyberknife and from 9.7 to 38.3 (mean 21.7) for IMRT. Results obtained with the new index confirmed the behavior observed with the conformity index. Conclusion: Conformity resulted in general better for the Cyberknife while homogeneity resulted in general better for IMRT. The ratio between volumes of mid-low isodose surfaces (10% – 50%) to the volume of the reference isodose surface (80%) resulted higher for IMRT than for the Cyberknife.
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Purpose: To measure doses delivered outside of the irradiated volume for typical CyberKnife treatments and to compare the results to peripheral doses arising from similar Gamma Knife (GK) and IMRT treatments. Method and Materials: CyberKnife treatment plans were developed for two hypothetical lesions in an anthropomorphic phantom, one in the thorax and another in the brain. In both cases, 500 cGy was prescribed to the 70% isodose line. Li‐F TLD‐100 capsules were placed within the phantom at various depths and distances from the irradiated volume. For the brain lesion, GK and 6‐MV IMRT treatment plans were also developed, and peripheral doses were measured. Results: Peripheral doses for the CyberKnife thorax treatment ranged from 3.3±0.13% to 1.2±0.06% of the prescribed dose (D p ) at distances between 15 and 43 cm from the edge of the target. For the target in the brain, CyberKnife peripheral doses ranged from 1.2±0.02% to 0.32±0.02% of D p at distances between 18 and 71 cm from the target edge. In comparison, the GK peripheral dose ranged from 0.63±0.03% to 0.053±0.002% of D p , and the IMRT plan resulted in doses between 0.19±0.004% and 0.043±0.002% of D p over the same range of distances. Conclusion : Doses outside the irradiated volume for Cyberknife treatments are significantly higher than those encountered in standard radiation therapy. Peripheral doses given in AAPM Task Group Report No. 36 (Stovall, et al. Med. Phys. 22:63–82, 1995) for a 6‐MV beam are between 0.2% and 0.02% of the dose at d max at a distances ranging from 20 to 70 cm from the edge of a 5×5cm 2 field. Furthermore, for the same target in the brain, CyberKnife peripheral doses were a factor of 2 to 6 times larger than those for GK, and a at least a factor of 6 times larger than those for IMRT.
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Stereotactic radiosurgery is a non-invasive technique that utilizes precisely targeted radiation as an alternative surgical tool. Conventional radiosurgery devices, such as Gamma Knife and X-Knife, rely upon skeletally attached stereotactic frames to immobilize the patient and accurately localize intracranial neoplasm. The CyberKnife (Accuray, Inc., Sunnyvale, California), a new and revolutionary stereotactic radiosurgery instrument, makes it possible to administer radiosurgery without a frame. The superiorities of the CyberKnife, including real-time image-guided irradiation and dynamic synchronous tracking, extend stereotactic radiosurgery for a range of extracranial tumors and some non-neoplastic disorders. This paper reviews CyberKnife technology and its clinical application in intracranial neoplasm and extracranial tumors.
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Since its introduction nearly 60 years ago, stereotactic radiosurgery has become the standard of care for the noninvasive destruction of intracranial tissues or lesions that may be inaccessible or unsuitable for open surgery. Today, modern stereotactic radiosurgery is practiced using advanced image guided treatment planning and specialized delivery systems including micro‐ MLC equipped linacs, CyberKnife, and Gamma Knife machines. Stereotactic radisourgery delivers a large dose to a precisely defined volume in a short time, and as such requires the utmost attention to precision and quality assurance. Also critical is the meticulous design of treatment processes that eliminate the possibility of potentially disastrous errors. In this presentation we review the fundamental aspects of stereotactic targeting and delivery, the technologies for stereotactic localization and treatment of cranial targets, and the quality assurance aspects associated with establishing and maintaining a clinical radiosurgery program. Examples of radiosurgery cases will be presented from the best practice sites utilizing Gamma Knife, CyberKnife, and linac delivery systems, followed by an expert panel discussion of quality measures for treatment planning and delivery. Learning Objectives: 1. Differentiate how radiation is delivered for Gamma Knife, CyberKnife and Linac‐based (conventional and robotic) stereotactic radiosurgery. 2. Define the treatment planning parameters, imaging requirements and workflow for Gamma Knife, CyberKnife and Linac‐based stereotactic radiosurgery. 3. Discuss measures for assuring accuracy in stereotactic localization and dose delivery for Gamma Knife, CyberKnife and Linac‐based stereotactic radiosurgery. 4. Discuss uncertainties and limitations associated with Gamma Knife, CyberKnife and Linac‐based stereotactic radiosurgery
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