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

Abstract

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.PACS number(s): 87.55.D‐, 87.55.km, 87.55.Qr, 87.56.Fc

Evaluation of the 4D RADPOS dosimetry system for dose and position quality assurance of CyberKnife

“…The SD of the Synchrony correlation error along any direction was ≤0.2 mm on average, indicating that CyberKnife's predictive model precisely reproduces fiducial (i.e., target) motion. This level of positional measurement agreement is consistent with CyberKnife tracking errors that other groups have found for the case of sinusoidal motion . If in turn, we look at the data for Model‐Fiducial which compares the same position datasets as the Synchrony correlation error but has had the coordinate alignment algorithm applied to the data, we see that in the primary direction of motion, z‐ direction (ANT/POST) and in the x direction (SUP/INF) the average SD of the differences is also ≤0.2 mm, however, in the y direction (LFT/RGT) the errors are higher (0.6 mm average SD).…”

Impacts of respiratory phase shifts on motion‐tracking accuracy of the CyberKnife Synchrony™ Respiratory Tracking System

“…In this study, we also evaluated the impacts of the update of the correlation models by changing the interval of the KV image acquisitions. This evaluation was possible because our technique evaluates the treatment x‐ray beams, although other techniques using laser or head‐mounted camera cannot use TLS during measurements.…”

“…Many previous studies have investigated the motion‐tracking accuracy of the SRTS . Inoue et al investigated the tracking accuracy using a video camera mounted on the CyberKnife head .…”

“…Inoue et al investigated the tracking accuracy using a video camera mounted on the CyberKnife head . Sumida et al evaluated the tracking accuracy by observing the laser mounted on the linac head . These works measured laser or moving ball instead of measuring the treatment beams.…”

Evaluation of the accuracy of the CyberKnife Synchrony™ Respiratory Tracking System using a plastic scintillator

“…Therefore, a real‐time evaluation technique for evaluating tracking accuracy is needed. Although a few studies have reported techniques to evaluate dynamic tracking errors using a video camera mounted on the linac head or laser equipped on the linac, these methods did not evaluate the radiation beams.…”