Room: AAPM ePoster Library
Purpose: To describe the clinical implementation of Varian’s triggered imaging via auto beam hold (ABH) to monitor the intra-fraction motion of soft tissues with implanted fiducials.
Methods: Varian’s triggered imaging option was activated on a Truebeam STx. A block of aquaplast with implanted fiducials was formed as a simple prostate phantom for commissioning testing. A gating box simulated respiratory motion. Kilo-voltage (kV) planer x-rays were acquired by the on-board imager at certain intervals of either gantry angle rotation, monitor units, time, or phase of the respiratory cycle. ABH localizes the fiducial on the kV image, and then measures the fiducial’s coincidence with its corresponding contour projected onto the kV image from the planning CT scan. If the coincidence of any localized fiducial and its projected contour is outside a preset tolerance, ABH will interrupt the mega-voltage (MV) beam, otherwise the treatment will continue uninterrupted. Triggered imaging via ABH was tested on prostate patients with the intent of expanding its use to liver, pancreas, kidneys and other abdominal organs by coupling it with the Varian real-time position management system to account for respiratory motion.
Results: Commissioning of the triggered imaging via ABH showed excellent coincidence between the fiducials and the projected contours on the kV images. Fiducial localization was inconsistent when overlapping with other fiducials or attenuating structures. Prostate patient testing showed the AHB recognized as high as 6 mm difference between the localized fiducials and their projected contours, and interrupted the MV beam allowing for repositioning.
Conclusion: Varian’s triggered imaging via ABH can detect intra-fraction motion and interrupt the MV beam for repositioning. Trigging imaging positions should avoid the fiducials overlapping with other attenuating structures. Triggered imaging could also provide clinics with similar intra-fraction motion information as magnetic resonance imaging capable linear accelerators.