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Medical Physics / Volume 39 / Issue 1 / RADIATION IMAGING PHYSICS

Med. Phys. 39, 4 (2012); http://dx.doi.org/10.1118/1.3664006 (14 pages)

Fast time-of-flight camera based surface registration for radiotherapy patient positioning

Simon Placht

Metrilus GmbH, Henkestr. 91, 91052 Erlangen, Germany and Pattern Recognition Lab, Friedrich Alexander University Erlangen-Nuremberg, Martensstr. 3, 91058 Erlangen, Germany

Joseph Stancanello

German Research Cancer Centre, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany

Christian Schaller and Michael Balda

Metrilus GmbH, Henkestr. 91, 91052 Erlangen, Germany

Elli Angelopoulou

Pattern Recognition Lab, Friedrich Alexander University Erlangen-Nuremberg, Martensstr. 3, 91058 Erlangen, Germany

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(Received 18 March 2011; accepted 7 November 2011; revised 7 November 2011; published online 9 December 2011)

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Purpose: This work introduces a rigid registration framework for patient positioning in radiotherapy, based on real-time surface acquisition by a time-of-flight (ToF) camera. Dynamic properties of the system are also investigated for future gating/tracking strategies.
Methods: A novel preregistration algorithm, based on translation and rotation-invariant features representing surface structures, was developed. Using these features, corresponding three-dimensional points were computed in order to determine initial registration parameters. These parameters became a robust input to an accelerated version of the iterative closest point (ICP) algorithm for the fine-tuning of the registration result. Distance calibration and Kalman filtering were used to compensate for ToF-camera dependent noise. Additionally, the advantage of using the feature based preregistration over an “ICP only” strategy was evaluated, as well as the robustness of the rigid-transformation-based method to deformation.
Results: The proposed surface registration method was validated using phantom data. A mean target registration error (TRE) for translations and rotations of 1.62 ± 1.08 mm and 0.07° ± 0.05°, respectively, was achieved. There was a temporal delay of about 65 ms in the registration output, which can be seen as negligible considering the dynamics of biological systems. Feature based preregistration allowed for accurate and robust registrations even at very large initial displacements. Deformations affected the accuracy of the results, necessitating particular care in cases of deformed surfaces.
Conclusions: The proposed solution is able to solve surface registration problems with an accuracy suitable for radiotherapy cases where external surfaces offer primary or complementary information to patient positioning. The system shows promising dynamic properties for its use in gating/tracking applications. The overall system is competitive with commonly-used surface registration technologies. Its main benefit is the usage of a cost-effective off-the-shelf technology for surface acquisition. Further strategies to improve the registration accuracy are under development.

© 2012 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

The work was supported by the International Max Planck Research School for Optics and Imaging (Erlangen, Germany). The evaluation on the linear accelerator was gratefully approved by Siemens Healthcare (Erlangen, Germany).

Article Outline

  1. INTRODUCTION
  2. MATERIALS AND METHODS
    1. Processing pipeline
      1. Distance correction
      2. Kalman filtering
      3. Body segmentation
      4. Surface registration algorithms
    2. Evaluation setup
    3. Robustness to deformations
  3. RESULTS
    1. Distance correction benefit
    2. Patient positioning accuracy and robustness
    3. Robustness to deformations
    4. Runtime aspects: Positioning and tracking modes
  4. DISCUSSION
    1. Comparative evaluation
    2. Clinical applications
  5. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3664006

KEYWORDS and PACS

Keywords

calibration, cameras, deformation, image registration, iterative methods, Kalman filters, medical image processing, noise, phantoms, radiation therapy, surface structure, radiotherapy, registration, surface features, Kalman filtering, time-of-flight cameras

PACS

  • 87.57.nj

    Registration

  • 06.20.fb

    Standards and calibration

  • 02.60.-x

    Numerical approximation and analysis

  • 87.53.Jw

    Therapeutic applications, including brachytherapy

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
William R. Hendee, Editor
Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
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College Park, Maryland 20740
301-209-3352

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