Evaluation of tracking accuracy of the CyberKnife system using a webcam and printed calibrated grid.

Tracking accuracy for the CyberKnife's Synchrony system is commonly evaluated using a film-based verification method. We have evaluated a verification system that uses a webcam and a printed calibrated grid to verify tracking accuracy over three different motion patterns. A box with an attached printed calibrated grid and four fiducial markers was attached to the motion phantom. A target marker was positioned at the grid's center. The box was set up using the other three markers. Target tracking accuracy was evaluated under three conditions: 1) stationary; 2) sinusoidal motion with different amplitudes of 5, 10, 15, and 20 mm for the same cycle of 4 s and different cycles of 2, 4, 6, and 8 s with the same amplitude of 15 mm; and 3) irregular breathing patterns in six human volunteers breathing normally. Infrared markers were placed on the volunteers' abdomens, and their trajectories were used to simulate the target motion. All tests were performed with one-dimensional motion in craniocaudal direction. The webcam captured the grid's motion and a laser beam was used to simulate the CyberKnife's beam. Tracking error was defined as the difference between the grid's center and the laser beam. With a stationary target, mean tracking error was measured at 0.4 mm. For sinusoidal motion, tracking error was less than 2 mm for any amplitude and breathing cycle. For the volunteers' breathing patterns, the mean tracking error range was 0.78-1.67 mm. Therefore, accurate lesion targeting requires individual quality assurance for each patient.

Crystallization and preliminary X-ray crystallographic studies of mavicyanin from Cucurbita pepo medullosa.

Mavicyanin isolated from Cucurbita pepo medullosa is a glycosylated protein containing a single polypeptide chain of 109 amino-acid residues and is a member of the phytocyanin subclass of cupredoxins. Non-glycosylated recombinant mavicyanin, which was expressed in Escherichia coli, was crystallized by the hanging-drop vapour-diffusion method with ammonium sulfate as the precipitant at pH 5.5. The crystals belonged to the hexagonal space group P6(1) (or P6(5)), with unit-cell parameters a = 64.0, c = 245.0 A, four molecules per asymmetric unit and a solvent content of 59%. X-ray diffraction data were collected to 1.6 A resolution. To solve the structure of mavicyanin, the MAD method as well as a Patterson search method using the structure of stellacyanin as a starting model are presently being utilized.