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C.A. Amstutz, J.H. Kowal, L.–P. Nolte, M.H. Foerster; Intra–Operative Localization of Tantalum Markers for Proton Beam Irradiation by an Optoelectronic Navigation System . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2259.
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© ARVO (1962-2015); The Authors (2016-present)
Proton beam irradiation is an established treatment modality for intraocular tumours such as choroidal melanoma. Precise planning and delivery of the charged particle beam are mandatory to deliver the necessary radiation dose to the tumour tissue, but to spare the surrounding tissue. Usually, different image modalities such as fundus photographs, ultrasound images, and computer tomography or magnetic resonance image data are combined to develop the treatment plan. Often tantalum marker elements are sutured to the globe in a preceding operation to co–register the different image modalities and to position the patient eye for irradiation. The relative position of the tantalum markers and their distance to the limbus are important parameters for the planning and are usually measured intra–operatively by a pair of compasses.
Optoelectronic navigation systems allow for accurate digitization of spatial points with respect to a dynamic reference coordinate system. To establish the reference system, optoelectronic markers, mounted on a suction ring device, were attached to the eye. We describe the use of the system to localize the spatial position of the tantalum markers with respect to each other and with respect to anatomical landmarks of the eye, such as the limbus or the optic nerve.The marker position with respect to the tumour mass can be defined by digitizing tumour borders emphasized by diaphanoscopy. Digitizing scleral surface points can assess globe geometry.
The method was verified on porcine eye specimens. Accuracy of the tantalum marker digitization was determined and proved to be in the order of 0.15mm. No margin of error greater than 0.33 was measured for different configurations. Application of the suction ring did not significantly change the digitization results. For four patients undergoing tantalum marker surgery, application of the system delivered additional and complementary geometric data for the planning of the charged particle irradiation.
Optoelectronic navigation systems are a feasible tool for precise intraoperative localization of tantalum markers and anatomic landmarks. The 3–dimensional position information that is obtained by such a system can be used in the treatment planning for charged particle irradiation, and possibly increases the accuracy of radiation delivery.
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