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Accuracy and Reproducibility of Fixation Light Positioning for Gaze Stabilization in Proton Therapy of Intraocular Tumors

R Ricotti1 , A Pella1*, R Via2 , B Tagaste1 , A Giorgetto1 , M Fiore1 , M Ciocca1 , F Valvo81/sup> , R Orecchia1 , G Baroni3 (1) Centro Nazionale di Adroterapia Oncologica (CNAO), Pavia, PV, Italy (2) Politecnico di Milano, Milan, MI, Italy (3) Centro Nazionale di Adroterapia Oncologica (CNAO), Pavia, PV , Italy and Politecnico di Milano, Milan, MI, Italy


(Sunday, 7/29/2018) 3:00 PM - 3:30 PM

Room: Exhibit Hall | Forum 5

Purpose: At our Institution, ocular proton therapy (OPT) is delivered using a non-dedicated beamline. For minimizing dose to critical structures, an optimal gaze direction (polar and azimuthal angles) is established during treatment planning. An eye tracking system (ETS) is used to provide a fixation light (FL) for the stabilization of gaze direction and to monitor eye motion. To accurately position the ETS and thus the FL, industrial robots (Mitsubishi RV-2F-D and RV-4FL-D) and optical tracking systems (OTS) are used. We verify the accuracy and reproducibility of the technological platform for FL positioning in OPT.

Methods: The ETS alignment is required during computed tomography (CT) scan acquisition and during irradiation. The ETS is hooked to two different industrial robots, one mounted on CT couch and the other fixed on robotic treatment chair. Given the optimal polar and azimuthal angles of gaze direction, an initial ETS alignment is performed automatically by the industrial robots. Then, the OTS provides guidance to the desired ETS position through real-time tracking of a configuration of 14 passive radiopaque markers attached to the ETS.The accuracy of FL position was retrospectively investigated measuring the ETS orientation on CT scans acquired after its alignment. Ten ETS configurations with 33° and 40° of polar angle and azimuthal angles ranging between 0°-180° were tested. The reproducibility of ETS position was assessed in treatment room directly with the OTS, after multiple robot handling and treatment chair docking /undocking.

Results: Median errors of 0.9° (range: -0.2°─1.3°) polar and 0.6° (range: -0.7─1.2°) azimuthal angles respectively were found. Repeatability tests highlighted the ability of the robot and treatment chair to reposition the ETS with errors < 0.2 °.

Conclusion: The developed technologies for ETS positioning feature an accuracy inferior to one degree in fixation light alignment and increases the efficiency of the treatment workflow.


Not Applicable / None Entered.


TH- External Beam- Particle therapy: Proton therapy - Development (new technology and techniques)

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