Sparse Active Triangulation Grids for Respiratory Motion Management

The management of respiratory motion poses a challenge to a variety of medical applications. In radiation therapy, studies have shown that external body motion correlates with the internal tumor position. Based on a patient-specific model learnt prior to the first fraction, the tumor location can be inferred from an external surrogate during treatment, superseding intra-fractional radiographic imaging. Existing solutions rely on a single 1D respiratory surrogate and exhibit a limited level of accuracy due to inter-cycle variation. Recent work indicated that considering multiple regions would yield an enhanced model. Hence, we propose a novel solution based on a single-shot active triangulation sensor (Flying Triangulation, Ettl et al., Appl Opt 51 (2012) 281-289) that acquires a sparse grid of 3D measurement lines in real time, using two perpendicular laser line pattern projection systems. Building on non-rigid point cloud registration, the elastic displacement field representing the torso deformation with respect to a reference is recovered. This displacement field can then be used for model-based tumor tracking. We present measurement results and non-rigid displacement fields.