Evolution of dose distribution for a 125I eye plaque using MCNPX and Plaque Simulator software

Objective: Eye plaque radiation therapy is the treatment of choice for small- and medium-sized choroidal melanomas. This study investigated the dose distribution around eye plaques containing I-125 seeds to treat ocular melanoma using Monte Carlo N-Particle eXtended (MCNPX) and Plaque Simulator (PS) software. Methods: Dosimetry evaluation and comparison of the resulting isodose curves for I-125 COMS plaques were performed using the MCNPX code. The isodose curves and dose distributions were calculated using PS treatment planning for a I-125 COMS plaque. Results: In the validation, the maximum relative difference between the results of this study and those reported in other literature was approximately 9%-10% for the COMS plaques. The dose distributions of MCNPX were lower than those of PS with a relative difference of approximately 27.7%-35.4%. The dose distribution may differ depending on the I-125 source spectra and seed design used in the two methods. In addition, the dose algorithm used in PS made a major contribution to the relative differences between the results. Conclusion: The PS did not provide accurate details of dose distribution near the surface of the plaque insert. The source parameters used in each program should be studied more carefully to determine the source of the differences in the estimated dose values.