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Purpose: Eye-dedicated proton therapy (PT) facilities are used to treat malignant intraocular lesions, especially uveal melanoma (UM). The first commercial ocular PT beamline from Varian was installed in the Netherlands. In this work, the conceptual design of the new eyeline is presented. In addition, a comprehensive comparison against five PT centers with dedicated ocular beamlines is performed, and the clinical impact of the identified differences is analyzed. Material/Methods: The HollandPTC eyeline was characterized. Four centers in Europe and one in the United States joined the study. All centers use a cyclotron for proton beam generation and an eye-dedicated nozzle. Differences among the chosen ocular beamlines were in the design of the nozzle, nominal energy, and energy spectrum. The following parameters were collected for all centers: technical characteristics and a set of distal, proximal, and lateral region measurements. The measurements were performed with detectors available in-house at each institution. The institutions followed the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)-398 Code of Practice for absolute dose measurement, and the IAEA TRS-398 Code of Practice, its modified version or International Commission on Radiation Units and Measurements Report No. 78 for spread-out Bragg peak normalization. Energy spreads of the pristine Bragg peaks were obtained with Monte Carlo simulations using Geant4.Seven tumor-specific case scenarios were simulated to evaluate the clinical impact among centers: small, medium, and large UM, located either anteriorly, at the equator, or posteriorly within the eye. Differences in the depth dose distributions were calculated. | 7 CHARACTERIZATION OF THE HOLLANDPTC PROTON THERAPY BEAMLINE DEDICATED TO UVEAL MELANOMA TREATMENT AND AN INTERINSTITUTIONAL COMPARISON How to cite this article: Fleury E, Trnková P, Spruijt K, et al. Characterization of the HollandPTC proton therapy beamline dedicated to uveal melanoma treatment and an interinstitutional comparison. Med Phys.

Purpose Dose, fractionation, normalization and the dose profile inside the target volume vary substantially in pulmonary stereotactic body radiotherapy (SBRT) between different institutions and SBRT technologies. Published planning studies have shown large variations of the mean dose in planning target volume (PTV) and gross tumor volume (GTV) or internal target volume (ITV) when dose prescription is performed to the PTV covering isodose. This planning study investigated whether dose prescription to the mean dose of the ITV improves consistency in pulmonary SBRT dose distributions. Materials and methods This was a multi-institutional planning study by the German Society of Radiation Oncology (DEGRO) working group Radiosurgery and Stereotactic Radiotherapy. CT images and structures of ITV, PTV and all relevant organs at risk (OAR) for two patients with early stage non-small cell lung cancer (NSCLC) were distributed to all participating institutions. Each institute created a treatment plan with the technique commonly used in the institute for lung SBRT. The specified dose fractionation was 3 × 21.5 Gy normalized to the mean ITV dose. Additional dose objectives for target volumes and OAR were provided. Results In all, 52 plans from 25 institutions were included in this analysis: 8 robotic radiosurgery (RRS), 34 intensity-modulated (MOD), and 10 3D-conformal (3D) radiation therapy plans. The distribution of the mean dose in the PTV did not differ significantly between the two patients (median 56.9 Gy vs 56.6 Gy). There was only a small difference between the techniques, with RRS having the lowest mean PTV dose with a median of 55.9 Gy followed by MOD plans with 56.7 Gy and 3D plans with 57.4 Gy having the highest. For the different organs at risk no significant difference between the techniques could be found. Conclusions This planning study pointed out that multiparameter dose prescription including normalization on the mean ITV dose in combination with detailed objectives for the PTV and ITV achieve consistent dose distributions for peripheral lung tumors in combination with an ITV concept between different delivery techniques and across institutions.

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PURPOSE:To develop a method to calculate the angle λ of the human eye using Zernike tilt measurements in specular reflection corneal topography. METHODS:The meaning of Zernike tilt in specular reflection corneal topography is demonstrated by measurements on translated artificial surfaces using the VU Topographer. The relationship derived from the translation experiments is used to determine the angle λ. Corneal surfaces are measured for a set of eight different fixation points, for which tilt angles ρ are obtained from the Zernike tilt coefficients. The angles ρ are used with respect to the fixation target angles to determine angle λ by fitting a geometrical model. This method is validated with Orbscan II's angle-κ measurements in 9 eyes. RESULTS:The translation experiments show that the Zernike tilt coefficient is directly related to an angle ρ, which describes a tilt orientation of the cornea and can therefore be used to derive a value for angle λ. A significant correlation exists between measured values for angle λ with the VU Topographer and the angle κ with the Orbscan II (r=0.95, P<0.001). A Bland-Altman plot indicates a mean difference of -0.52 degrees between the two instruments, but this is not statistically significant as indicated by a matched-pairs Wilcoxon signed-rank test (P≤0.1748). The mean precision for measuring angle λ using the VU topographer is 0.6±0.3 degrees. CONCLUSION: The method described above to determine angle λ is sufficiently repeatable and performs similarly to the angle-κ measurements made with the Orbscan II. RESUMEN OBJETIVO:Desarrollar un método para calcular el ángulo λ del ojo humano utilizando el coeficiente de Zernike de tilt (inclinación del frente de onda) medido mediante topografía corneal por reflexión especular. MÉTODOS:El significado del término de tilt del desarrollo de Zernike en topografía corneal especular queda demostrado por medio de medidas realizadas con el Topógrafo VU en superficies artificiales desplazadas transversalmente. La relación que se deriva de los experimentos de traslación se utiliza para determinar el ángu-lo λ. Se realizan medidas de la superficie corneal para ocho puntos de fijación diferentes. Para cada uno de ellos se obtiene el ángulo ρ de tilt (inclinación) a partir del correspondiente coeficiente de Zernike de tilt. El conjunto de ángulos ρ se utiliza con respecto a los ángulos que forman los puntos de fijación correspondientes para determinar el ángulo λ, ajustando para ello un modelo geométrico. Este método se valida comparando los resultados con medidas del ángulo κ realizadas con el Orbscan II en 9 ojos. RESULTADOS: Los experimentos de traslación demuestran que el coeficiente de Zernike de tilt está directamente relacionado con un ángulo ρ, el cual describe la inclinación global de la córnea y, por lo tanto, se puede utilizar para derivar el valor del ángulo λ. Existe una correlación significativa entre los valores del ángulo λ medidos con el Topógrafo VU y los valores del ángulo κ medidos con el Orbscan II (r=0,95; P<0,001)...