No abstract

Radiosurgery is defined as the delivery of high doses of ionising radiation, in mono-or hypo-fractionated treatments, to destroy tumours or focal areas of pathology. The clinical requirements of designing a radiosurgical treatment system include providing: a) a highly precise beam delivery to targets located throughout the body, b) a highly conformal dose distribution, c) the ability to irradiate both small and/or large complex-shaped lesions while minimising the dose to adjacent radiosensitive tissues and d) the ability to interactively track lesion motion due to normal patient motion. To accomplish this, the CyberKnifeH radiosurgery system has pioneered in this area by taking advantage of the inherent geometrical targeting precision of a commercial arm-based robotic system carrying a compact X-band linear accelerator and integrated with X-ray imaging and visualisation feedback systems. The arm-mounted linear accelerator, equipped with patient specific anatomical models, registered to the patient in real-time with image guidance, dynamically and safely delivers conformal and homogeneous radiation for therapeutic benefit. This paper details the components of the CyberKnife system and their integration in the clinical workflow of radiosurgery.

It is known that good CT reconstructions require that many views of the scanned object be obtained, where each view consists of many rays which traverse the patient. It is known that the required number of views depends on the diameter of the region reconstructed and the spatial resolution achieved. We present a new analysis of this question, valid for reconstruction from fan beam views, which shows that larger fan angles will require more views. Computer simulations, using a fan beam reconstruction algorithm, confirmed the predicted fan angle dependence and demonstrated that streak artifacts will result if too few views are used. The effect is also demonstrated experimentally by a phantom scan on a clinical CT scanner. Implications for clinical CT scanning are discussed.

The usefulness of a smoothed reconstruction CT algorithm was studied using raw data from the EMI Mark I head scanner. The reconstruction algorithm operated on an off-line computer, independent of the EMI algorithm. This technique greatly reduces image noise and improves the visibility of very low-contrast structures, but at the cost of reduced spatial resolution. Phantom tests with contrasts as low as 0.14% demonstrated the validity of the images. Clinical results showed greatly improved visualization of gray and white matter with no increase in dose. It was necessary to expand the CT density scale so that the range from air to water was divided into 2,000 parts.