Does The Tumor Motion Width Affect The Performance of Cyberknife Synchrony® Respiratory Tracking System?: Three Dimensional Dosimetric Analysis Using Polymer Gel Dosimeter
Purpose: The aim of this study is to investigate the performance of Synchrony respiratory motion tracking system (RMTS) of Cyberknife® robotic radiosurgery unit for different movement widths using polymer gel dosimetry.
Materials and Methods: BrainLab Gating lung phantom was used to simulate lung movements with three different amplitudes of 1 cm, 2 cm and 3 cm. Three fiducials were inserted to the phantom for tracking of a tumor of 1X1X1 cm3. The MultiPlan® treatment planning system (TPS) of Cyberknife® was used to deliver 4 Gy to the target. Radiochromic film and polymer gel dosimetry were used and measurements were compared with the dose distributions acquired from the TPS. The dose information of irradiated gel were read out using 1.5 T magnetic resonance imaging. The gamma index values were analysed using the Ashland FilmQA Pro 3.0 software for film dosimeters and Polygevero software for gel dosimeters using the 3mm/3% criteria. Polygevero gamma index value of ≤1 is accepted as a passing criteria according to the literature.
Results: The mean 3 mm/3% gamma index values of film dosimetry were 92.6±1.94%, 91.0±4.00%, 90.3±2.04% for tumor motions of 1 cm, 2 cm and 3 cm, respectively (p<0.001). For polymer gel dosimetry, the mean gamma index values calculated over almost three million points were 0.56±0.10, 0.60±0.24 and 0.65±0.30 for tumor motions of 1 cm, 2 cm and 3 cm, respectively (p<0.001). Although the difference was statistically significant for 3 different amplitudes, the performance of the system was within the acceptance limits.
Conclusion: Three dimensional performance analysis showed that Cyberknife Synchrony® RMTS is successful in tumor tracking regardless of the amplitude of movement.
*This study is supported by The Scientific and Technological Research Council Of Turkey (TUBITAK) 3001 project, project number 115S446