ESTRO 2023 - Abstract Book

S1637

Digital Posters

ESTRO 2023

E.Y. Han 1 , D.J. Rhee 1 , S. Krafft 1 , T. Briere 1

1 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston, USA

Purpose or Objective ExacTrac Dynamic is an in-room X-ray and surface/thermal imaging device that offers X-ray and surface-based positioning and monitoring. The purpose of this study was to verify surface tracking and X-ray imaging accuracy through an end-to-end test following intentional motions for two treatment workflows. The accuracy of surface tracking on phantoms with various skin tone and textures was also studied. Materials and Methods A 2-target stereotactic brain treatment plan was delivered with Standard X-ray workflow and CBCT positioning with X-ray monitoring workflow. The plan was generated for an RTsafe head phantom, and an ionization chamber was placed at the center of the superior target with a 1.3 cm radius. The phantom was placed on a motorized motion platform to create four discrete intra-fractional motions while beam was on. Both measurements were compared to a measurement without ExacTrac and intra-fractional motion (reference). To verify the accuracy of surface tracking for various skin stones (bright/dark), textures (dry/moist) and camera temperature equilibrium states (state B [camera on <10min] and state C [>1hr]), we measured the difference between surface tracking and X-ray image registration for bright- and dark-skinned phantoms. The bright/dark-skinned phantom was simulated by applying a makeup foundation to the surface of the RTsafe head phantom (Figure 1). After stereoscopic x-ray imaging reset the surface tracking to the planned position, the phantom position is changed and the discrepancy of surface tracking against X-ray imaging were recorded. The measurements were repeated for couch angles of 0°, 45°, and 270°.

Figure 1 Motion platform with dark(a) and bright-skinned phantom(b), surface imaging with bright(c), dark and moist(d) and dark and dry-skinned phantom(e). Results Measured doses were 2078 cGy for X-ray workflow and 2053 cGy for CBCT workflow. Both measured doses were within 1.4% of the reference measured dose (2082 cGy). We observed that the tracking accuracy was compromised due to surface degradation and region-of-interest flickering for the dark moist-skinned phantom with extended time (camera state C). This caused fluctuations in surface tracking and false beam interlocks (Figure 1). The difference between X-ray and surface imaging was about 0.17±0.11mm/0.03±0.05° for the bright-skinned phantom, whereas those for the dark dry-skinned phantom were 0.26±0.14mm/0.05±0.09° and for the dark moist-skinned phantom 0.53±0.21mm/0.07±0.08°. The differences were larger for couch angles of 0° and 45° in the lateral and longitudinal directions (Table 1).