Monte Carlo dosimetry for /sup 125/I and /sup 60/Co in eye plaque therapy

Monte Carlo calculations of radiation dosimetry using m-smcapso-smcapsr-smcapss-smcapse-smcaps code are performed for /sup 125/I and /sup 60/Co point sources in a cylindrical head phantom that simulates the geometry of eye plaque therapy for choroidal melanoma. We obtain the dose variation in the eye at submillimeter intervals over distances as close as 1 mm and up to 2.5 cm from the source. The calculations for /sup 125/I are performed for the phantom media of water, protein, and a homogenized protein--water mixture simulating the composition of the eye. Relative dose functions for /sup 125/I for these phantom media are fitted to second-degree polynomials. Agreement is found with published results. The relative dose function for /sup 60/Co at eye position in the water head phantom is fitted to a third-degree polynomial and compared with that for /sup 60/Co at the center of a large water sphere. A boundary effect due to the head phantom--air interface on the dose distribution for /sup 60/Co is demonstrated. The dose falloff with distance is faster for the eye geometry compared with the bulk geometry. We also show that the relative dose distributions within the tumor are comparable for /sup 125/I and /sup 60/Co by comparing their relativemore » dose functions. This result is consistent with the success of clinical trials of large melanoma treatments with /sup 125/I plaques.« less