title: Estimating soft tissue thickness from light-tissue interactions--a simulation study.
abstract: Immobilization and marker-based motion tracking in radiation therapy often cause decreased patient comfort. However, the more comfortable alternative of optical surface tracking is highly inaccurate due to missing point-to-point correspondences between subsequent point clouds as well as elastic deformation of soft tissue. In this study, we present a proof of concept for measuring subcutaneous features with a laser scanner setup focusing on the skin thickness as additional input for high accuracy optical surface tracking. Using Monte-Carlo simulations for multi-layered tissue, we show that informative features can be extracted from the simulated tissue reflection by integrating intensities within concentric ROIs around the laser spot center. Training a regression model with a simulated data set identifies patterns that allow for predicting skin thickness with a root mean square error of down to 18 µm. Different approaches to compensate for varying observation angles were shown to yield errors still below 90 µm. Finally, this initial study provides a very promising proof of concept and encourages research towards a practical prototype.
authors.affiliation: Institute for Robotics and Cognitive Systems, University of Luebeck, Ratzeburger Allee 160, 23562 Luebeck, Germany ; Graduate School for Computing in Medicine and Life Sciences, University of Luebeck, Ratzeburger Allee 160, 23562 Luebeck, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wissel
authors.forename: Ralf
authors.initials: R
authors.lastname: Bruder
authors.forename: Achim
authors.initials: A
authors.lastname: Schweikard
authors.forename: Floris
authors.initials: F
authors.lastname: Ernst
keywords: (100.5010) Pattern recognition; (170.1610) Clinical applications; (170.3660) Light propagation in tissues; (170.6935) Tissue characterization; (280.0280) Remote sensing and sensors