SU‐E‐T‐123: Evaluation of Integrated Gating Systems on a Novalis Tx System Using Quantitative Motion Tracking Analyses and Efficient Time‐Delay Measurements

Purpose: To investigate accuracy of motion tracking and radiation delivery controlling of integrated gating systems on a Novalis Tx system. Methods: The study was performed on a Novalis Tx system, which is equipped with Varian RPM and BrainLAB ExacTrac gating systems. In this study, the two systems were assessed on accuracy of both motion tracking and radiation delivery controlling. To evaluate motion tracking, one artificial sinusoidal profile and three patients' respiratory profiles were used. The motion trajectories acquired by the two gating systems were compared against the references. To assess radiation delivery controlling, time‐delays were measured using a single‐exposure method. More specifically, radiation is delivered with a 4‐mm diameter cone within 10%–45% phases for BrainLAB ExacTrac system and within 0%–25% phases for Varian RPM system during expiration, each with three times. Radiochromic films were used to record the radiation exposures and to calculate the time‐delays. In the work, the discrepancies were quantified using mean and standard deviation (SD). Pearson's product moment correlational analysis was used to test correlation, which is quantified using a parameter of r. Results: The trajectory profiles acquired by the gating systems show good agreement with those references. A quantitative analysis shows that the average mean discrepancy between BrainLAB ExacTrac system and known references is 1.68 mm for artificial and patient profiles, with the maximum motion amplitude of 28.0 mm. As for Varian RPM system, the corresponding average mean discrepancy is 1.54 mm for artificial and patient profiles. With the single‐exposure method, the time‐delays are found to be 0.20±0.03 seconds and 0.09±0.01 seconds for BrainLAB ExacTrac and Varian RPM systems, respectivelyConclusions: The results indicate the gating systems on the Novalis Tx system can track motion and control radiation delivery with reasonable accuracy. The single‐exposure method has been demonstrated feasible in measuring time‐delays efficiently.