CyberKnife® Radiosurgery: A Higher Order of Precision
Treatment Margins
Because of its closeness to the diaphragm, the liver moves considerably with respiration. Even sophisticated stereotactic radiation approaches do not fully overcome the problem of respiration-induced target volume motion in liver lesions, causing the necessary application of a larger therapeutic margin to compensate, which also increases the dose to adjacent normal liver and in some cases, stomach, duodenum, small intestine and large intestine, potentially increasing the risk of radiation injury. Though adaptive methods such as shallow breathing or radiotherapy gating to the respiratory cycle have been used to reduce respiration-induced marginal dose degradation, they have not eliminated it.
Targeting Angles
Whereas traditional radiotherapy systems target the lesion from a relatively small number of fixed positions, the inherently noncoplanar geometry of the CyberKnife® device allows literally hundreds of targeting angles to be selected, increasing the ability to conform the ablative dose to the target lesion(s) within the liver, while better sparing the surrounding hepatic tissue.
Lesion Tracking
The CyberKnife® Synchrony® Respiratory Tracking System locks onto implanted gold fiducial markers and correlates their position with the respiratory cycle as determined by optical tracking, to track the targeted lesion with 1.5 mm accuracy, allowing a smaller applied margin compared with other stereotactic radiation delivery systems, giving CyberKnife the distinction of being the only device that currently brings radiosurgical precision to respiration-induced moving targets.
Technical Summary:
The CyberKnife® device brings an unprecedented level of radiation dose shaping and targeting precision, effectively bringing radiosurgical ablation capability to liver lesions, while minimizing the risk of serious injury to normal hepatic parynchema and adjacent tissues.
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