Optical eye tracking system for noninvasive and automatic monitoring of eye position and movements in radiotherapy treatments of ocular tumors

Abstract

A noninvasive eye tracking system based on infrared 3-D video-oculographic techniques is proposed for the automatic monitoring of eye position and orientation in external beam radiotherapy of ocular tumors. The presented method can be applied for the real-time estimation of lesion position and tumor-beam misalignments, allowing automatic patient setup and eye movement gated treatments. A prototypal eye tracker was developed and tested on five subjects, achieving gaze estimation errors of 0.5° and eye monitoring frequencies of 125 Hz. The proposed application can potentially improve quality and efficacy of ocular radiotherapy treatments, currently based on invasive, qualitative, and manual control procedures.

The National Centre for Oncological Hadrontherapy (CNAO): Status and perspectives

“…The eye tracker is based on non-invasive 3D video-oculography (VOG) techniques, by detecting ocular features on the video images captured by a pair of calibrated cameras [49]. The recognition of pupil contour and corneal reflections produced by two nearinfrared (NIR) light sources allows the estimation of pupil and cornea centers in 3D, which are used to reconstruct an eyeball local coordinate system.…”

Noninvasive referencing of intraocular tumors for external beam radiation therapy using optical coherence tomography: A proof of concept

“…6). Fassi et al 14 reported an average angular accuracy of 0.5 • evaluated based on five human subjects. With an average registration error below 0.36 • for tilting even with a sparse sampling of 125 × 125 A-scans, the proposed method yields improved angular accuracy for tilting.…”

“…In the past, different approaches have been applied including suction devices, 9 retro-or parabulbar anaesthesia, 10 or active fixation of light points. [11][12][13][14] Suction devices are very uncomfortable and may cause damage to the anterior eye segment. Local anaesthesia is associated with discomfort for the patient and induces displacement of the eyeball in the orbit.…”

“…In 2012 Fassi et al 14 proposed a direct 3D (threedimensional) approach providing quantitative information on the 3D position and orientation of the monitored eye using a stereoscopic camera system and two corneal reflections. After applying this eye tracking technique during CT and MRI scanning and after calibration of the eye tracker with respect to the treatment delivery system, the eye model can be transformed into the isocentric reference frame.…”

Optical eye tracking system for real‐time noninvasive tumor localization in external beam radiotherapy

“…The ETS is based on noninvasive 3D video-oculography (VOG) and is capable of detecting ocular features on the video image stream coming from a pair of calibrated cameras. 18,19 The system stems from a first prototype described by Fassi et al; 20 it features a new design compatible with clinical usability and incorporates specific algorithms for the automatic detection of torsional eye movements, which were found to be relevant in laser refractive surgery. Liu et al, 21 and Kim and Joo 22 reported median eye cyclotorsion of 3 • between seated and supine positions with values higher than 5 • on 20% of the investigated cases.…”