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      Monte Carlo Computation of Dose-Volume Histograms in Structures at Risk of an Eye Irradiated with Heterogeneous Ruthenium-106 Plaques

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          Background/Aims: The aim of this work is to compare Monte Carlo simulated absorbed dose distributions obtained from <sup>106</sup>Ru eye plaques, whose heterogeneous emitter distribution is known, with the common homogeneous approximation. The effect of these heterogeneities on segmented structures at risk is analyzed using an anthropomorphic phantom. Methods: The generic CCA and CCB, with a homogeneous emitter map, and the specific CCA1364 and CCB1256 <sup>106</sup>Ru eye plaques are modeled with the Monte Carlo code PENELOPE. To compare the effect of the heterogeneities in the segmented volumes, cumulative dose-volume histograms are calculated for different rotations of the aforementioned plaques. Results: For the cornea, the CCA with the equatorial placement yields the lowest absorbed dose rate while for the CCA1364 in the same placement the absorbed dose rate is 33% higher. The CCB1256 with the hot spot oriented towards the cornea yields the maximum dose rate per unit of activity while it is 44% lower for the CCB. Conclusions: Dose calculations based on a homogeneous distribution of the emitter substance yield the lowest absorbed dose in the analyzed structures for all plaque placements. Treatment planning based on such calculations may result in an overdose of the structures at risk.

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          Most cited references 23

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          Eye shape in emmetropia and myopia.

          To determine axial, vertical, and horizontal eye dimensions in myopic and emmetropic eyes by using magnetic resonance imaging (MRI) and to relate these to different ocular expansion models of myopia development. The internal length (cornea to retina), height and width (both retina to retina) were measured in emmetropic and myopic eyes (up to -12 D) of 88 participants aged 18 to 36 years. Participants were positioned supine in a clinical MRI scanner. The fixation target was imaged straight ahead of the subject by an overhead 45 degrees inclined mirror. Eye images were acquired with a 7.5-cm receive-only radio frequency surface coil. Axial (horizontal through middle of eye) and sagittal (vertical through visual axis) sections were taken with a T(1)-weighted fast spin-echo sequence. With an increase in myopic refractive correction, myopic eyes became much larger in all three dimensions, but more so in length (0.35 mm/D, 95% confidence interval [CI] 0.28-0.40) than in height (0.19 mm/D, 95% CI 0.09-0.29) and more so in height than in width (0.10 mm/D, 95% CI 0.01-0.20). Based on height and length dimensions, 25% and 29% of myopic eyes exclusively fitted global expansion and axial elongation models, respectively. Based on width and length dimensions, 17% and 39% of myopic eyes exclusively fitted the global expansion and axial elongation models, respectively. Although there are considerable individual variations, in general myopic eyes are elongated relative to emmetropic eyes, more in length than in height and even less in width. Approximately a quarter of the myopic participants fitted each of the global expansion or axial elongation model exclusively. The small proportions are due primarily to the large variability in the dimensions of emmetropic eyes.
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            The American Brachytherapy Society consensus guidelines for plaque brachytherapy of uveal melanoma and retinoblastoma.

            To present the American Brachytherapy Society (ABS) guidelines for plaque brachytherapy of choroidal melanoma and retinoblastoma.
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              Ruthenium brachytherapy for uveal melanoma, 1979-2003: survival and functional outcomes in the Swedish population.

              To evaluate observed and relative survival rates, enucleation rates, and visual outcome after ruthenium 106 brachytherapy for uveal melanoma. Retrospective cases series from the Swedish national referral center. Five hundred seventy-nine patients (579 eyes) with choroidal or ciliary body melanomas, including 55 tumors more than 7 mm in height, treated with ruthenium episcleral plaques from January, 1979, through April, 2003. Clinical and radiotherapy data were extracted from a dedicated database, and survival status was determined through population registries. Tumor size was classified according to the Collaborative Ocular Melanoma Study criteria. The 5- and 10-year relative survival rates were estimated, and univariate and multivariate regression models were constructed for predictive factors on observed survival, enucleation, and visual deterioration. Observed and relative survival rate, proportion of secondary enucleation, deterioration of visual acuity to less than 0.5, respectively, to 0.1 or worse. Tumors were classified as small in 10.5%, medium in 78.4%, and large in 9.2% of patients. The 5- and 10-year observed overall survival rates were 83.3% and 71.5%, respectively, and the corresponding relative rates were 95.5% and 94%, respectively. Factors predicting survival were tumor diameter, patient age, and secondary enucleation. One hundred six patients (18%) underwent enucleation up to 14 years after plaque treatment. The only predictive factor for enucleation was tumor size. At 5 years, 31% of the patients retained 0.5 visual acuity or better, and 49% retained better than 0.1 visual acuity. Predictive factors for visual deterioration were visual acuity and distance from posterior tumor border to the foveola. After ruthenium brachytherapy for uveal melanoma, the survival rates and visual outcomes in this population-based investigation were similar to previously published results. The eye was retained in 81.7% of patients. Careful patient selection (presently we only treat melanomas 7 mm or smaller in height) and life-long monitoring for recurrences is warranted.

                Author and article information

                Ocular Oncology and Pathology
                S. Karger AG
                October 2020
                20 July 2020
                : 6
                : 5
                : 353-359
                aFaculty of Medicine, University of Duisburg-Essen, Essen, Germany
                bFakultät Physik, Technische Universität Dortmund, Dortmund, Germany
                cNCTeam, Strahlenklinik, Universitätsklinikum Essen, Essen, Germany
                dWest German Proton Therapy Center Essen (WPE), Essen, Germany
                eWest German Cancer Center (WTZ), Essen, Germany
                fUniversity Hospital Essen, Essen, Germany
                gGerman Cancer Consortium (DKTK), Essen, Germany
                hDepartment of Particle Therapy, University Hospital Essen, Essen, Germany
                Author notes
                *Lorenzo Brualla, West German Proton Therapy Center Essen (WPE), Hufelandstrasse 55, DE–45147 Essen (Germany), lorenzo.brualla@uni-due.de
                508113 Ocul Oncol Pathol 2020;6:353–359
                © 2020 S. Karger AG, Basel

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                Page count
                Figures: 8, Pages: 7
                Research Article


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