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The Benefit of Adjunct CT Imaging in Clip-Based Treatment of Ocular Melanoma with Protons

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r slopsema

R Slopsema1*, M Mamalui1 , M Rutenberg1 , D Yeung1 , Z Li1 , J Bolling2 , S Flampouri1 , R Dagan1 , (1) University of Florida Health Proton Therapy Institute, Jacksonville, FL, (2) Mayo Clinic, Jacksonville, FL

Presentations

TH-CD-BRA-1 (Thursday, July 16, 2015) 10:00 AM - 12:00 PM Room: Ballroom A


Purpose: To evaluate if addition of CT imaging to the treatment-planning process of ocular-melanoma proton therapy will improve the accuracy of target localization.
Methods: For a total of 30 patients a treatment plan is made according to the standard protocol: 1) the ophthalmologist sutures 3-5 small clips on the eye surface; 2) during simulation, a set of orthogonal images is taken identifying the clip positions; 3) the treatment-planning software (EyePlan) fits a geometric eye model to the imaged clips; 4) in the model the tumor is delineated based on the clip positions and registered fundus photographs; 5) dose from the treatment beam is calculated using 2.5 mm margins. In this study an additional high-resolution CT scan is taken of each treated eye. The geometric eye model is registered to the CT based on the clip positions. Agreement of the anatomy (lens, sclera, optic nerve) is evaluated. The translation required to go from the clip-based to anatomy-based registration is determined as measure of the accuracy of clip position in the radiograph-based model. A second treatment plan is made based on the CT clip positions. Target coverage and dose to critical structure is compared between the radiograph-based and CT-based plan. Dose deviations are evaluated for correlation with visual acuity, clip location, and tumor size.

Results: For 19 patients the shift in clip position between radiograph-only and CT-based simulation is ≤1 mm; for 28 patients ≤2 mm. For the remaining two patients it is 3.6 and 5.0 mm. For most patients (18) the effect on the tumor coverage is minimal: reduction in V99% of ≤2.5 %. For 3 patients V99% reduces by >7.5%.

Conclusion: The addition of CT imaging to standard planning protocols improves target coverage in 10% of patients.


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