Three‐dimensional MRI‐based treatment planning approach for non‐invasive ocular proton therapy

Abstract

Purpose To develop a high‐resolution three‐dimensional (3D) magnetic resonance imaging (MRI)‐based treatment planning approach for uveal melanomas (UM) in proton therapy. Materials/methods For eight patients with UM, a segmentation of the gross tumor volume (GTV) and organs‐at‐risk (OARs) was performed on T1‐ and T2‐weighted 7 Tesla MRI image data to reconstruct the patient MR‐eye. An extended contour was defined with a 2.5‐mm isotropic margin derived from the GTV. A broad beam algorithm, which we have called πDose, was implemented to calculate relative proton absorbed doses to the ipsilateral OARs. Clinically favorable gazing angles of the treated eye were assessed by calculating a global weighted‐sum objective function, which set penalties for OARs and extreme gazing angles. An optimizer, which we have named OPT’im‐Eye‐Tool, was developed to tune the parameters of the functions for sparing critical‐OARs. Results In total, 441 gazing angles were simulated for every patient. Target coverage including margins was achieved in all the cases (V95% > 95%). Over the whole gazing angles solutions space, maximum dose (Dmax) to the optic nerve and the macula, and mean doses (Dmean) to the lens, the ciliary body and the sclera were calculated. A forward optimization was applied by OPT’im‐Eye‐Tool in three different prioritizations: iso‐weighted, optic nerve prioritized, and macula prioritized. In each, the function values were depicted in a selection tool to select the optimal gazing angle(s). For example, patient 4 had a T2 equatorial tumor. The optimization applied for the straight gazing angle resulted in objective function values of 0.46 (iso‐weighted situation), 0.90 (optic nerve prioritization) and 0.08 (macula prioritization) demonstrating the impact of that angle in different clinical approaches. Conclusions The feasibility and suitability of a 3D MRI‐based treatment planning approach have been successfully tested on a cohort of eight patients diagnosed with UM. Moreover, a gaze‐angle trade‐off dose optimization with respect to OARs sparing has been developed. Further validation of the whole treatment process is the next step in the goal to achieve both a non‐invasive and a personalized proton therapy treatment.

MR imaging characteristics of uveal melanoma with histopathological validation

“…It is important to be aware that the limits of flat tumors are difficult to determine with both US and MRI. Moreover, the radiotherapy planning of UM with complex tumor shapes, such as some tumors with a mushroom configuration, is more difficult and deserves special attention [20]. The mushroom configuration is associated with breaks in Bruch's membrane [11,21].…”

Clinical Outcomes after International Referral of Uveal Melanoma Patients for Proton Therapy

“…It is complicated to isolate the impact of dose parameters of eye structures that are in proximity, and it is therefore hard to determine whether the current planning strategy is suboptimal or not. Encouraging developments in the field of magnetic resonance imaging of the eye may enable more precise proton therapy planning in the near future [ 44 , 45 , 46 ].…”

“…Future studies should aim to further improve visual outcomes and reduce side effects. The integration of high-resolution imaging in proton therapy treatment planning will be a key step in this journey [ 45 ]. This and other studies showed that distant metastasis are common and impair overall survival.…”

Non-Cancer Effects following Ionizing Irradiation Involving the Eye and Orbit

“…Focalized radiotherapy techniques ensure a better control of dose delivery within the tumor, decreasing unnecessary irradiation of the surrounding healthy tissues and reducing radiation-induced vision loss. For this, better imaging systems, such as OCT technologies, choroidal doppler holography, and high-resolution magnetic resonance imaging (MRI), might increase the accuracy of the detection of tumor margins and ensure a precise delineation of the OAR [ 14 , 124 , 125 , 126 ]. Another way to retain visual function is preventive personalized treatment.…”