John R. Dooley

The CyberKnife Robotic Radiosurgery System in 2010.

This review provides a complete technical description of the CyberKnife® VSI™ System, the latest addition to the CyberKnife product family, which was released in September 2009. This review updates the previous technical reviews of the original system version published in the late 1990s. Technical developments over the last decade have impacted virtually every aspect of the CyberKnife System. These developments have increased the geometric accuracy of the system and have enhanced the dosimetric accuracy and quality of treatment, with advanced inverse treatment planning algorithms, rapid Monte Carlo dose calculation, and post-processing tools that allow trade-offs between treatment efficiency and dosimetric quality to be explored. This review provides a system overview with detailed descriptions of key subsystems. A detailed review of studies of geometric accuracy is also included, reporting a wide range of experiments involving phantom tests and patient data. Finally, the relationship between technical developments and the greatly increased range of clinical applications they have allowed is reviewed briefly.

4D Treatment Optimization and Planning for Radiosurgery with Respiratory Motion Tracking

The CyberKnife® Robotic Radiosurgery System (Accuray Incorporated, Sunnyvale, CA) can treat targets that move with respiration using the Synchrony® Respiratory Motion Tracking System or the Xsight ℳ Lung Tracking System (Accuray Incorporated, Sunnyvale, CA). Alignment of each treatment beam with the moving target is maintained in real time by moving the beam dynamically with the target. The challenges of treatment planning for mobile targets are different for dynamic respiratory motion tracking than for conventional approaches such as motion-encompassing and respiratory gating methods that are common on gantry -based delivery de vices. Internal motion during respiration is not rigid, and thus positions of critical structures relative to the target and hence to the beam can change during respiration. The 4D Treatment Optimization and Planning feature, which recently became available in the MultiPlan® (Accuray Incorporated, Sunnyvale, CA) Treatment Planning System, is a new approach to four-dimensional (4D) treatment planning for motion tracking. It uses a 4D-CT image study to measure respiratory tissue motion and deformation and to account for the effect of motion and deformation on dose. The individual 3D-CT images are aligned so that the target coincides in each image. A tissue motion model is computed by performing non rigid registration of the individual 3D-CT images. Using the target -centric alignment and the deformation model, it is possible to calculate a dose distribution that takes into account both beam movement and soft tissue deformation. This dose distribution may be calculated before plan optimization and hence used to determine the desired beam geometry and weighting, or it may be calculated after plan optimization in order to review the effects of respiration on the dose isocontours and statistics for a given plan.

Deformable registration of abdominal CT images: tissue stiffness constraints using B-splines

One method of modelling respiratory motion of the abdomen is to acquire CT images at different points in the respiratory cycle and develop a deformation model that gives a mapping between corresponding anatomical points in the images. In this work, we use such a method, and the target application is radiosurgery, particularly radiosurgical treatment of lesions that move during respiration, for example those in the liver, lung, or pancreas. In order to accurately calculate the treatment dose, it is necessary to have a good deformation map both globally and locally (in the vicinity of the treatment target). We use a dual-resolution method in order to allow a more accurate deformation model to be computed in the region of interest. We also introduce a tissue stiffness constraint, along with an application of matrix algebra that allows this constraint to be applied in an effective way with respect to the control point values.