Room: Exhibit Hall
Purpose: COMS and EyePhysics (EP) plaques have been used with Â¹Â²â?µI seeds for many years. The aim of this study was to investigate dosimetric coverage of different radionuclides for improved tumor control probability and minimization of healthy tissue dose.
Methods: Simulations of 2D and 3D dose distributions using MCNP6 estimated with the *F4 track length estimator with tally modifiers and NIST mass-energy absorption coefficients. Photon energy spectra for Â¹â?°Â³Pd, Â¹Â²â?µI, and Â¹Â³Â¹Cs were taken from the National Nuclear Data Center and included all source photons > 1 keV. A 10-cm diameter homogeneous water medium contained the seeds, COMS Silastic, and gold alloy (COMS or EP plaques). A (0.1 mm)Â² sampling mesh provided 2D dose distributions, CAX depth-dose, and DVHs for assessment of the tumor and scleral doses. COMS plaques (14-mm and 16-mm diameters) and EP plaques (based on model EP917) with 0.65-mm and 0.92-mm slot depths were simulated with the three radionuclides. Tumor depth was 5 mm and the doses were normalized to the tumor apex to deliver 100 Gy. Dose quality metrics (Dâ‚‰â‚ˆ for the tumor and Dâ‚?â‚€ for the OARs) were evaluated from DVHs and CAX depth-dose were then compared.
Results: The deep-slotted EP917 plaques delivered higher uniform doses with greater conformity to the tumor compared to the COMS plaques for all three radionuclides. Dâ‚?â‚€ ratios of tumor with the COMS plaques and EP917 for Â¹â?°Â³Pd were 1.48 and 1.38, respectively. Â¹â?°Â³Pd delivered higher (max. 9%) CAX depth dose compared to Â¹Â²â?µI, and Â¹Â³Â¹Cs up to 5 mm depth. Scleral surface dose with the EP917 plaque was >2 times higher than from the COMS plaques.
Conclusion: For the dosimetry, radionuclide choice was less influential than the plaque design. The deep-slotted EP917 plaque with Â¹â?°Â³Pd showed the highest dose uniformity compared to the other plaque designs and radionuclide choices.
Monte Carlo, Brachytherapy, Eye Plaques
Not Applicable / None Entered.