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The Influence of Eye Plaque Design On Dose Distributions and Dose-Volume Histograms

P Aryal

P Aryal1*, JA Molloy1 , MJ Rivard2 , (1) Univ Kentucky, Lexington, KY, (2) Tufts Univ School of Med, Boston, MA


WE-A-17A-12 Wednesday 7:30AM - 9:30AM Room: 17A

Purpose: To investigate the effect of slot design of the model EP917 plaque on dose distributions and dose-volume histograms (DVHs).

Methods: The dimensions and orientation of the slots in EP917 plaques were measured. In the MCNP5 radiation simulation geometry, dose distributions on orthogonal planes and DVHs for a tumor and sclera were generated for comparisons. 27 slot designs and 13 plaques were evaluated and compared with the published literature and the Plaque Simulator clinical treatment planning system.

Results: The dosimetric effect of the gold backing composition and mass density was < 3%. Slot depth, width, and length changed the central axis (CAX) dose distributions by < 1% per 0.1 mm in design variation. Seed shifts in the slot towards the eye and shifts of the ¹²⁵I-coated Ag rod within the capsule had the greatest impact on CAX dose distribution, increasing by 14%, 9%, 4%, and 2.5% at 1, 2, 5, and 10 mm, respectively, from the inner sclera. Along the CAX, dose from the full plaque geometry using the measured slot design was 3.4% ± 2.3% higher than the manufacturer-provided geometry. D₁₀ for the simulated tumor, inner sclera, and outer sclera for the measured plaque was also higher, but 9%, 10%, and 20%, respectively. In comparison to the measured plaque design, a theoretical plaque having narrow and deep slots delivered 30%, 37%, and 62% lower D₁₀ doses to the tumor, inner sclera, and outer sclera, respectively. CAX doses at -1, 0, 1, and 2 mm were also lower by a factor of 2.6, 1.4, 1.23, and 1.13, respectively.

Conclusion: The study identified substantial sensitivity of the EP917 plaque dose distributions to slot design. However, it did not identify substantial dosimetric variations based on radionuclide choice (¹²⁵I, ¹⁰³Pd, or ¹³¹Cs). COMS plaques provided lower scleral doses with similar tumor dose coverage.

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