Fifty-sixth annual meeting of the American association of physicists in medicine
WE-G-BRF-02: Geometrical Verification of Real-Time Tumor Tracking Using Fast MV Fluoroscopy On a New Generation EPID: Investigating the Influence of Pulsing Artifacts and Artifact Suppression Techniques On Fiducial Marker and Marker-Less Soft-Tissue Detection
to investigate the influence of megavolt (MV) pulse artifacts and pulsing artifact suppression techniques on fiducial marker and marker-less detection success for verification of real-time tumor tracking (RTTT) on a gimbaled linac system using fast MV fluoroscopy.
Because frame rates on current clinical available EPIDs is limited to 7.5 Hz, a new generation EPID (XRD-1642 AP19) with a maximum frame rate of 30 Hz was evaluated for RTTT verification. Both 0.5 mm and 0.75 mm Visicoil™ markers were used for MV marker tracking with a frame rate of respectively 7.5 Hz, 15 Hz and 30 Hz. Additionally, marker-less tumor tracking was conducted and compared with the ground-truth fiducial marker motion. Static markers under influence of increasing phantom thickness and dynamic (sine and human irregular) motion was used to investigate performance of MV target detection.For each MV sequence, the free running (FR-nF) (ignoring MV pulsing during readout) acquisition mode was compared with two acquisition modes aiming to reduce MV pulsing artifacts, i.e. combined wavelet-FFT filtering (FR-wF) and a hardware synchronized (S-nF) readout with respect to the MV pulses.
For a 0.75 mm visicoil, deviations of sine wave motion were sub-millimeter (RMSE <0.8 mm) for 15-30 Hz MV fluoroscopy, independent of the acquisition mode (FR-nF, Fr-wF and S-nF). For marker-less tumor detection, FR-nF images resulted in RMSE >3 mm, while for MV fluoroscopy in S-mode RMSE <1.0 mm for 15 Hz and RMSE <1.6 mm for 30 Hz.
In general, marker contrast was decreased in function of higher frame rates. For a sufficient marker thickness, highest detection success was obtained, even during fast breathing motion, with a frame rate of 30 Hz. Furthermore, a synchronized readout provided most accurate detection of a marker-less soft-tissue structure during RTTT, while 0.75 mm Visicoils were not influenced by pulsing artifacts.
Research was sponsored by the Flemish Government through Hercules Foundation and corporate funding from BrainLab AG. Testing equipment was received through a loaner agreement with PerkinElmer Optoelectronics (Germany) and the support of Mitsubishi Heavy Industries.