Accuracy evaluation of CatalystTM, a 3d surface imaging device designed for set up guidance and on-line target monitoring for tomotherapy treatments

Abstract

Introduction Highly conformal helical treatments require a daily MV image for patient repositioning. Additional dose related to MV image guidance is evaluated at 1 to 3cGy per fraction. Over the last years, non-irradiant optical imaging technics have been developed such as Catalyst TM . This system designed for handling patient positioning and intra-fraction motion detection is based on principles of photogrammetry and optical triangulation. With knowledge of the surface movements, a volumetric deformable model is used to predict the influence on the actual target position. Our study aims to compare accuracy of Catalyst TM system against MVCT one and to develop an efficient procedure for clinical routine. Material and methods In this study, repositioning deviations were measured by Catalyst TM on 2 groups of 10 patients treated by Tomotherapy, for pelvic and thoracic locations. For each patient, positioning accuracy using Catalyst TM was evaluated comparing deviations calculated by Catalyst TM to MVCT versus reference scan registration results. Regarding to the validation of the on-line tracking, deviations between pre- and post-treatment images were compared against the results of the on-line motion tracking system. Systematic residual error was also investigated and quantified using a thoracic phantom. Results A clinical efficient procedure has been developed for surface image acquisition. The process takes less than 5 min per treatment fraction. Mean deviations for patient setup between MVCT and Catalyst TM system obtained for 2 patients during 3 fractions are: 2.5 mm in left-right direction, 2.8 mm in cranio-caudal direction, 3.8 mm in antero-posterior and less than 1.5° for all rotations. Conclusion This study will allow us to determine localization that benefits the most of Catalyst TM 3D surface imaging device and for which it may be possible to avoid MV daily imaging keeping the same PTV margins.