The CyberKnife in clinical use: current roles, future expectations.

The CyberKnife system deploys a linac mounted on an agile robot and directed under image guidance for stereotactic radiotherapy using nonisocentric beam delivery. A design advantage of the CyberKnife system is its method of active image guidance during treatment delivery. Recent developments in the hardware and software of the system have significantly enhanced its functionality: (a) an optimized path traversal process significantly reduces the robot motion time, resulting in reductions of overall treatment times of at least 5-10 min; (b) to optimize the accuracy of dose calculation in CyberKnife planning/delivery, Monte Carlo algorithms have been introduced; (c) the new IRIS collimator reduces the monitor units required, increases treatment speed and improves conformality and homogeneity of treatment plans; (d) XSight lung tracking, an algorithm for fiducial-less lung tracking, has been developed for peripheral, radio-dense lung tumors with diameters >15 mm; and (e) a sequential optimization planning process incorporates a more flexible approach to optimize the multiple, complex treatment planning criteria used today. The clinical efficacy of CyberKnife radiosurgery for brain/head lesions such as metastases, arteriovenous malformations, acoustic neuromas and meningiomas is well established. Since there is no need for skeletal fixation with the CyberKnife, radiosurgery can be applied to targets beyond the brain, and the technology has been extensively used for stereotactic body radiotherapy, treating targets in many anatomic sites. Currently, clinical studies have been completed or are ongoing for common malignancies including tumors involving the spine, lung, pancreas, liver and prostate.