Objective: Conventionally, ocular proton therapy (PT) is planned using measurements obtained by an ophthalmologist using ultrasound, fundoscopy, biometry, and intraoperative assessments. Owing to... Show moreObjective: Conventionally, ocular proton therapy (PT) is planned using measurements obtained by an ophthalmologist using ultrasound, fundoscopy, biometry, and intraoperative assessments. Owing to the recent advances in magnetic resonance imaging (MRI) of uveal melanoma (UM), it is possible to acquire high-resolution 3-dimensional images of the eye, providing the opportunity to incorporate MRI in ocular PT planning. In this study, we described how these measurements can be obtained using MRI, compared the MRI-based measurements with conventional ophthalmic measurements, and identified potential pitfalls for both modalities. Design: Cross-sectional study. Subjects: Data from 23 consecutive patients with UM treated with PT were retrospectively evaluated. Methods: Magnetic resonance imaging-based measurements of axial length, tumor height and basal diameter, and marker-tumor distances were compared with the conventional ophthalmic measurements, and discrepancies were evaluated in a multidisciplinary setting. Main Outcome Measures: Tumor prominence and basal diameters on MRI and ultrasound, axial length on MRI and biometry, tumor-marker distances on MRI and measured intraoperatively. Results: The mean absolute differences of the tumor height and basal diameter measurements between ultrasound and MRI were 0.57 mm and 1.44 mm, respectively. Larger absolute differences in height and basal diameter were observed when the full tumor extent was not visible on ultrasound (0.92 mm and 1.67 mm, respectively) compared with when the full tumor extent was visible (0.44 mm and 1.15 mm, respectively). When the full tumor was not visible on ultrasound, MRI was considered more reliable. Tumor-marker distances measured using MRI and intraoperative techniques differed < 1 mm in 55% of the markers. For anteriorly located and mushroom-shaped tumors (25% of the markers), MRI provided more accurate measurements. In flat UM (15% of the markers), however, it was difficult to delineate the tumor on MRI. The mean absolute difference in axial length between optical biometry and MRI was 0.50 mm. The presence of the tumor was found to influence optical biometry in 15 of 22 patients; the remaining patients showed a better agreement (0.30 mm). Magnetic resonance imaging-based biometry was considered more reliable in patients with UM. Conclusions: Magnetic resonance imaging allowed for the 3-dimensional assessment of the tumor and surrounding tissue. In specific patients, it provided a more reliable measurement of axial length, tumor dimensions, and marker-tumor distances and could contribute to a more accurate treatment planning. Never-theless, a combined evaluation remains advised, especially for flat UM. Show less
Background and Purpose: Three-dimensional (3D) Magnetic Resonance Imaging (MRI) is increasingly used to complement conventional two-dimensional ultrasound in the assessment of tumour dimension... Show moreBackground and Purpose: Three-dimensional (3D) Magnetic Resonance Imaging (MRI) is increasingly used to complement conventional two-dimensional ultrasound in the assessment of tumour dimension measurement of uveal melanoma. However, the lack of definitions of the 3D measurements of these tumour dimensions hinders further adaptation of MRI in ocular radiotherapy planning. In this study, we composed 3D MR-based definitions of tumour prominence and basal diameter and compared them to conventional ultrasound. Materials and methods: Tumours were delineated on 3DT2 and contrast-enhanced 3DT1 (T1gd) MRI for 25 pa-tients. 3D definitions of tumour prominence and diameter were composed and evaluated automatically on the T1gd and T2 contours. Automatic T1gd measurements were compared to manual MRI measurements, to auto-matic T2 measurements and to manual ultrasound measurements. Results: Prominence measurements were similar for all modalities (median absolute difference 0.3 mm). Auto-matic T1gd diameter measurements were generally larger than manual MRI, automatic T2 and manual ultra-sound measurements (median absolute differences of 0.5, 1.6 and 1.1 mm respectively), mainly due to difficulty defining the axis of the largest diameter. Largest differences between ultrasound and MRI for both prominence and diameter were found in anteriorly located tumours (up to 1.6 and 4.5 mm respectively), for which the tumour extent could not entirely be visualized with ultrasound. Conclusions: The proposed 3D definitions for tumour prominence and diameter agreed well with ultrasound measurements for tumours for which the extent was visible on ultrasound. 3D MRI measurements generally provided larger diameter measurements than ultrasound. In anteriorly located tumours, the MRI measurements were considered more accurate than conventional ultrasound. Show less
