Abstract

In this study, the dose distribution has been calculated for the Collaborative Ocular Melanoma Study (COMS) eye plaques at various diameters 10–22 mm, loaded with the 103-Pd brachytherapy seeds (Model IR06-103Pd). Several Monte Carlo (MC) simulations have been employed to carry out the gold backing and Silastic insert effect on dose distribution around the eye plaque. Version 5 of the Monte Carlo N-particle (MCNP) code has been used to carry out the simulations. The new palladium seed was modelled in three geometric orientations (ideal, vertical and diagonal). Results are compared with the calculated data for COMS eye plaque loaded with Theragenics model 200 and Best model 2335 palladium-103 seeds and model 6711 iodine-125 seeds. The calculated dose rate constant of the IR06-103Pd seed was found to be 0.692 0.020 cGy h<sup>1</sup> <sup>U</sup><sup>1</sup> . The air kerma strength to deliver 85 Gy to tumour apex in a water medium was found to be 4.10 U/seed. The dosimetric parameters calculated in this work for the new palladium seed indicate the IR06-103Pd seed is suitable for use in brachytherapy. In COMS plaques, the dose distribution to points of interest was compared for three 103-Pd seed models. With the exception of sclera dose and for a given prescription dose, the IR06 seed delivers lower dose ocular points of interest.

Keywords: eye plaque, palladium-103, brachytherapy, dosimetry
