ESTRO 36 Abstract Book

S231 ESTRO 36 _______________________________________________________________________________________________

Ridder 1 1 Universitair Ziekenhuis Brussel- Vrije Universiteit Brussel, Department of Radiotherapy, Brussels, Belgium 2 GZA Ziekenhuizen- Sint Augustinus – Iridium Kankernetwerk Antwerpen, Radiotherapy Department, Antwerpen, Belgium 3 Brainlab AG- Feldkirchen- Germany, R&D RT Motion Management, Munich, Germany 4 University Hospitals Leuven, Department of Radiation Oncology, Leuven, Belgium 5 Babes Bolyai University, Faculty of Physics, Cluj- Napoca, Romania Purpose or Objective Dynamic Wave Arc (DWA) is a system-specific non- coplanar arc technique that combines synchronized gantry-ring rotation with D-MLC optimization. This paper presents the clinical workflow, quality assurance program, and reports the geometric and dosimetric results of the first patient cohort treated with DWA. Material and Methods The RayStation TPS was clinically integrated on the Vero SBRT platform for DWA treatments. The main difference in the optimization modules of VMAT and DWA relates to angular spacing, where the DWA optimization algorithm does not consider the gantry spacing, but only the Euclidian norm of the ring and gantry angle. To support DWA deliveries, the Vero system required some additional upgrades: an MLC secondary feedback unit upgrade allowing faster dynamic MLC leaf movement of up to 4 cm/s at isocenter level, and a machine controller offering gantry-ring synchronous rotations. The first 15 patients treated with DWA represent a broad range of treatment sites: breast boost, prostate, lung SBRT and bone metastases, which allowed us to explore the potentials and assess the limitations of the current site-specific DWA template solution. Table 1 provides further information for each patient case including the corresponding DWA plan information, while Figure 1 presents the most common used DWA trajectories. For the DWA verification a variety of QA equipment was used, from 3D diode array to an anthropomorphic end-to-end phantom. The geometric accuracy of each arc was verified with an in-house developed method using fluoroscopy images.

The influence of the MRL fringe field is less than described by Kok for the pre-clinical prototype, but does still influence the beam steering of the accelerators in adjacent treatment rooms. The LUTs of 2 accelerators, that were situated the closest to the MRL, but outside the 0.5 Gauss line, needed to be adjusted in order to get beam parameters within tolerances. Adjusting the LUTs fully corrected the influence of the magnetic fringe field of the MRL. In case of an unexpected ramp down of the magnet (i.e. quench) both neighbouring accelerators cannot be used clinically before the LUTs are adjusted to the new situation. Adjustment of the LUT can be done in a short time by experienced personnel, without a dedicated measurement device.

References: Kok et al., Phys. Med. Biol. 54 (2009) N409–N415 OC-0439 Treating patients with Dynamic Wave Arc: first clinical experience M. Burghelea 1 , D. Verellen 2 , J. Dhont 1 , C. Hung 3 , K. Poels 4 , R. Van den Begin 1 , M. Boussaer 1 , K. Tournel 1 , C. Jaudet 1 , T. Reynders 1 , T. Gevaert 1 , V. Simon 5 , M. De