ESTRO 2024 - Abstract Book

S3766

Physics - Image acquisition and processing

ESTRO 2024

4 Wieser HP, Cisternas E, Wahl N, Ulrich S, Stadler A, Mescher H, ... & Bangert M. (2017). Development of the open ‐ source dose calculation and optimization toolkit matRad. Med Phys, 44(6), 2556-2568. https://doi.org/10.1002/mp.12251

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Fusion of optical and MR-imaging for ocular proton beam therapy planning

Corné Haasjes 1,2,3 , T.H. Khanh Vu 1 , Jan-Willem M. Beenakker 1,2,3

1 Leiden University Medical Center, Ophthalmology, Leiden, Netherlands. 2 Leiden University Medical Center, Radiology, Leiden, Netherlands. 3 Leiden University Medical Center, Radiation Oncology, Leiden, Netherlands

Purpose/Objective:

Conventionally Ocular Proton Therapy (OPT) is planned using a geometrical model based on peroperative and ophthalmic measurements. OPT planning can be improved by including fundoscopy images fused with 3D imaging data, such as MRI. Such a fusion is, however, currently not possible as fundus photographs are geometrically deformed by the eye’s optics. In this study we developed a method to correct for these deformations and assessed its accuracy in 27 subjects.

Material/Methods:

Optical raytracing simulations were performed in Ansys OpticStudio with ZOSPy [1]. Patient-specific eye models were constructed for 27 subjects with a wide range of ocular geometries (e.g. spherical equivalent of refraction errors up to -7 D). In these models the eye’s refraction, length, corneal geometry, lens location, curvature and thickness were obtained from the patient’s records. Retinal shape was determined from MR-images [2]. Fundus photography locations up to 85°, relative to the visual axis, were assessed. For each location, light rays were traced through the complete eye model, to obtain a ground truth mapping of locations on the fundus photographs to the corresponding retinal locations (Figure 1A). Subsequently a method was developed to obtain this mapping without optical raytracing. In this method, the second nodal point (an optical characteristic of the eye) was used as patient-specific reference point to link the fundus camera location to the retina. This method was compared to earlier proposed methods, used by the EYEPLAN ocular TPS [3] and the OPTOS wide-field fundus camera [4] (Figure 1B), methods that do not consider the patient-specific optical characteristics. Finally, the clinical applicability of the proposed second nodal point method is demonstrated in a uveal melanoma patient.

Results: