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Modernizing Proton Treatments for Ocular Melanoma

C Bloch

C Bloch1*, A Egan2 , J Saini2 , D Maes2 , T Wong2 , R Rengan1 , (1) University of Washington, Seattle, WA, (2) SCCA Proton Therapy Center, Seattle, WA


SU-I-GPD-T-200 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Proton therapy has been a successful modality for the treatment of ocular melanoma for decades. However, its continued use in current proton therapy centers is threatened for a variety of reasons, such as: lack of FDA approved treatment planning software, inability to evaluate impact of gaze angle prior to simulation, and discontinued construction of dedicated eye treatment lines. At our institution, we have employed a new method for treating ocular melanoma using a standard beam line and commercial software.

Methods: In approximately 1 year, 79 ocular patients were treated at our center. Patients were simulated on a CT scanner using a specially designed eye fixation device. Treatment planning was done using the standard XiO proton treatment planning system. Initial patients were treated with 2 or 3 beams, but this was reduced to a single anterior beam to more closely emulate successful historical treatments. Patients were treated in a Seated position in a conventional treatment room with two fixed beam lines. The beam was delivered through a standard IBA nozzle with a 10cm snout, originally with a standard aperture and compensator. More recently, a custom snout extension replaced the standard aperture and compensator to improve the beam properties.

Results: All patients were successfully treated from a technical standpoint. The custom snout extension provides significant improvements to the beam properties (distal falloff and penumbra) and more closely matches the parameters of dedicated eye lines. Additionally, it provides improved clearance for more optimal gaze angles.

Conclusion: The custom snout extension allows any aperture-based proton snout the ability to closely match the beam properties of a dedicated eye line. The XiO TPS can be used for dose calculation with our modified beam parameters. These developments build off historical success allowing modern proton centers to treat ocular melanoma patients without a dedicated eye line.

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