CyberKnife in the treatment of prostate cancer: a revolutionary system.

The CyberKnife is a frameless advanced robotic system that uses image-guided radiotherapy (IGRT) and adaptive radiotherapy (ART) for stereotactic radiosurgery technique in intraand extracranial lesions. The CyberKnife has also revolutionised the use of radiosurgery to treat tumours in different parts of the body. This system represents, after three-dimensional conformal radiotherapy (3DCRT), a new frontier in the treatment of prostate cancer, applying the same dosimetric and biologic considerations as with highdose-rate (HDR) brachytherapy. The CyberKnife combines three different advanced technologies to deliver frameless conformal radiosurgical doses. The first is a miniature linear accelerator (Linac X-6 MV) mounted on a robot arm (KUKA, Augsburg, Germany). The autonomous robot allows multiple positions and angles to deliver a series of up to 1560 different directions. The second innovation is real-time image guidance during treatment, using body landmarks or gold fiducials, to mark the target position to perform frameless radiosurgery in intracranial, spinal, and body sites. The registered image has been used to determine the treatment site’s coordinates with respect to the Linac robot and the target coordinates to the robot, with the beams to the tumour site. The third innovation is amorphous silicon detectors to establish patient position and orientation through body skeleton or gold fiducials. During treatment, two silicon cameras provide the actual image in real time, and they are compared with digitally reconstructed radiographs (DRR) obtained from computed tomography (CT) scan. The biologic rationale for hypofractioned radiotherapy is that the proliferation of prostate cancer cells is low, and these cells are sensitive to high doses. The data indicate that the a/b relationship of prostate neoplastic cells is