Dosimetric comparison of seed-less and multi-seed ¹²⁵I eye plaque: a Monte Carlo study

This study presents a comprehensive dosimetric comparison between Collaborative Ocular Melanoma Study (COMS) eye plaque containing ¹²⁵I seeds and a novel seed-less design plaque of similar shape and radioactive strength using high-precision Monte Carlo Technique. Monte Carlo-based dose distributions such as central axis depth dose, lateral off-axis dose profiles and 2-dimensional isodose distributions for three different plaque diameters 10, 14 and 20 mm are calculated and compared with the dose distributions of analogous seed-less plaques. This study also evaluates the influence of different seed Models on the dose distributions across 10, 14, and 20 mm plaque diameters. The results demonstrate that the dosimetric advantage of the seed-less design is independent of the specific seed model and dependent on the diameter of the plaques. Seed-less plaque of 10 mm diameter produces comparable dose distribution with the corresponding multi-seed plaque design. Seed-less plaques of 14 mm and 20 mm diameter deliver dose rates approximately twice as high as the corresponding multi-seed plaques. For large tumours, the seed-less design demonstrates superior dose retention at the tumour apex, maintaining 23.7% of the surface dose at a 10 mm depth compared to only 16.4% for multi-seed plaques. Furthermore, seed-less plaques exhibit a steeper lateral dose fall-off and reduced integral dose, significantly enhancing the sparing of adjacent organs at risk (OAR). By providing superior tumour dose uniformity and improved OAR protection, seed-less plaques represent a promising, dosimetrically superior alternative for management of large intraocular masses.