Monitoring of breathing motion in image-guided PBS proton therapy: comparative analysis of optical and electromagnetic t
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RESEARCH
Open Access
Monitoring of breathing motion in image-guided PBS proton therapy: comparative analysis of optical and electromagnetic technologies Giovanni Fattori1, Sairos Safai1, Pablo Fernández Carmona1, Marta Peroni1, Rosalind Perrin1, Damien Charles Weber1,2 and Antony John Lomax1,3*
Abstract Background: Motion monitoring is essential when treating non-static tumours with pencil beam scanned protons. 4D medical imaging typically relies on the detected body surface displacement, considered as a surrogate of the patient's anatomical changes, a concept similarly applied by most motion mitigation techniques. In this study, we investigate benefits and pitfalls of optical and electromagnetic tracking, key technologies for non-invasive surface motion monitoring, in the specific environment of image-guided, gantry-based proton therapy. Methods: Polaris SPECTRA optical tracking system and the Aurora V3 electromagnetic tracking system from Northern Digital Inc. (NDI, Waterloo, CA) have been compared both technically, by measuring tracking errors and system latencies under laboratory conditions, and clinically, by assessing their practicalities and sensitivities when used with imaging devices and PBS treatment gantries. Additionally, we investigated the impact of using different surrogate signals, from different systems, on the reconstructed 4D CT images. Results: Even though in controlled laboratory conditions both technologies allow for the localization of static fiducials with sub-millimetre jitter and low latency (31.6 ± 1 msec worst case), significant dynamic and environmental distortions limit the potential of the electromagnetic approach in a clinical setting. The measurement error in case of close proximity to a CT scanner is up to 10.5 mm and precludes its use for the monitoring of respiratory motion during 4DCT acquisitions. Similarly, the motion of the treatment gantry distorts up to 22 mm the tracking result. Conclusions: Despite the line of sight requirement, the optical solution offers the best potential, being the most robust against environmental factors and providing the highest spatial accuracy. The significant difference in the temporal location of the reconstructed phase points is used to speculate on the need to apply the same monitoring system for imaging and treatment to ensure the consistency of detected phases. Keywords: Respiratory motion, Optical tracking, Electromagnetic tracking, Proton therapy, Gantry, CT imaging
* Correspondence: [email protected] 1 Center for Proton Therapy, Paul Scherrer Institut, 5232 Villigen, PSI, Switzerland 3 Department of Physics, ETH-Hönggerberg, 8093 Zurich, Switzerland Full list of author information is available at the end of the article © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original au
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