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Title: Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy

Abstract

Purpose: External beam radiotherapy currently represents an important therapeutic strategy for the treatment of intraocular tumors. Accurate target localization and efficient compensation of involuntary eye movements are crucial to avoid deviations in dose distribution with respect to the treatment plan. This paper describes an eye tracking system (ETS) based on noninvasive infrared video imaging. The system was designed for capturing the tridimensional (3D) ocular motion and provides an on-line estimation of intraocular lesions position based on a priori knowledge coming from volumetric imaging. Methods: Eye tracking is performed by localizing cornea and pupil centers on stereo images captured by two calibrated video cameras, exploiting eye reflections produced by infrared illumination. Additionally, torsional eye movements are detected by template matching in the iris region of eye images. This information allows estimating the 3D position and orientation of the eye by means of an eye local reference system. By combining ETS measurements with volumetric imaging for treatment planning [computed tomography (CT) and magnetic resonance (MR)], one is able to map the position of the lesion to be treated in local eye coordinates, thus enabling real-time tumor referencing during treatment setup and irradiation. Experimental tests on an eye phantom and seven healthy subjectsmore » were performed to assess ETS tracking accuracy. Results: Measurements on phantom showed an overall median accuracy within 0.16 mm and 0.40° for translations and rotations, respectively. Torsional movements were affected by 0.28° median uncertainty. On healthy subjects, the gaze direction error ranged between 0.19° and 0.82° at a median working distance of 29 cm. The median processing time of the eye tracking algorithm was 18.60 ms, thus allowing eye monitoring up to 50 Hz. Conclusions: A noninvasive ETS prototype was designed to perform real-time target localization and eye movement monitoring during ocular radiotherapy treatments. The device aims at improving state-of-the-art invasive procedures based on surgical implantation of radiopaque clips and repeated acquisition of X-ray images, with expected positive effects on treatment quality and patient outcome.« less

Authors:
; ;  [1]; ; ; ;  [2]; ;  [3];  [4]
  1. Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano 20133 (Italy)
  2. CNAO Centro Nazionale di Adroterapia Oncologica, Pavia 27100 (Italy)
  3. Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano 20133, Italy and CNAO Centro Nazionale di Adroterapia Oncologica, Pavia 27100 (Italy)
  4. CNAO Centro Nazionale di Adroterapia Oncologica, Pavia 27100, Italy and European Institute of Oncology, Milano 20141 (Italy)
Publication Date:
OSTI Identifier:
22413542
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 42; Journal Issue: 5; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 60 APPLIED LIFE SCIENCES; ACCURACY; ALGORITHMS; COMPUTERIZED TOMOGRAPHY; CORNEA; EXTERNAL BEAM RADIATION THERAPY; MONITORING; NEOPLASMS; PHANTOMS; RADIATION DOSE DISTRIBUTIONS; TELEVISION CAMERAS

Citation Formats

Via, Riccardo, E-mail: riccardo.via@polimi.it, Fassi, Aurora, Fattori, Giovanni, Fontana, Giulia, Pella, Andrea, Tagaste, Barbara, Ciocca, Mario, Riboldi, Marco, Baroni, Guido, and Orecchia, Roberto. Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy. United States: N. p., 2015. Web. doi:10.1118/1.4915921.
Via, Riccardo, E-mail: riccardo.via@polimi.it, Fassi, Aurora, Fattori, Giovanni, Fontana, Giulia, Pella, Andrea, Tagaste, Barbara, Ciocca, Mario, Riboldi, Marco, Baroni, Guido, & Orecchia, Roberto. Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy. United States. doi:10.1118/1.4915921.
Via, Riccardo, E-mail: riccardo.via@polimi.it, Fassi, Aurora, Fattori, Giovanni, Fontana, Giulia, Pella, Andrea, Tagaste, Barbara, Ciocca, Mario, Riboldi, Marco, Baroni, Guido, and Orecchia, Roberto. Fri . "Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy". United States. doi:10.1118/1.4915921.
@article{osti_22413542,
title = {Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy},
author = {Via, Riccardo, E-mail: riccardo.via@polimi.it and Fassi, Aurora and Fattori, Giovanni and Fontana, Giulia and Pella, Andrea and Tagaste, Barbara and Ciocca, Mario and Riboldi, Marco and Baroni, Guido and Orecchia, Roberto},
abstractNote = {Purpose: External beam radiotherapy currently represents an important therapeutic strategy for the treatment of intraocular tumors. Accurate target localization and efficient compensation of involuntary eye movements are crucial to avoid deviations in dose distribution with respect to the treatment plan. This paper describes an eye tracking system (ETS) based on noninvasive infrared video imaging. The system was designed for capturing the tridimensional (3D) ocular motion and provides an on-line estimation of intraocular lesions position based on a priori knowledge coming from volumetric imaging. Methods: Eye tracking is performed by localizing cornea and pupil centers on stereo images captured by two calibrated video cameras, exploiting eye reflections produced by infrared illumination. Additionally, torsional eye movements are detected by template matching in the iris region of eye images. This information allows estimating the 3D position and orientation of the eye by means of an eye local reference system. By combining ETS measurements with volumetric imaging for treatment planning [computed tomography (CT) and magnetic resonance (MR)], one is able to map the position of the lesion to be treated in local eye coordinates, thus enabling real-time tumor referencing during treatment setup and irradiation. Experimental tests on an eye phantom and seven healthy subjects were performed to assess ETS tracking accuracy. Results: Measurements on phantom showed an overall median accuracy within 0.16 mm and 0.40° for translations and rotations, respectively. Torsional movements were affected by 0.28° median uncertainty. On healthy subjects, the gaze direction error ranged between 0.19° and 0.82° at a median working distance of 29 cm. The median processing time of the eye tracking algorithm was 18.60 ms, thus allowing eye monitoring up to 50 Hz. Conclusions: A noninvasive ETS prototype was designed to perform real-time target localization and eye movement monitoring during ocular radiotherapy treatments. The device aims at improving state-of-the-art invasive procedures based on surgical implantation of radiopaque clips and repeated acquisition of X-ray images, with expected positive effects on treatment quality and patient outcome.},
doi = {10.1118/1.4915921},
journal = {Medical Physics},
issn = {0094-2405},
number = 5,
volume = 42,
place = {United States},
year = {2015},
month = {5}
}