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Technical Note: Monte Carlo study of 106 Ru/ 106 Rh ophthalmic plaques including the 106 Rh gamma spectrum
Author(s) -
Hermida–López Marcelino,
Brualla Lorenzo
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12248
Subject(s) - monte carlo method , kerma , physics , nuclear medicine , cobalt 60 , radiation , gamma ray , dosimetry , materials science , chemistry , analytical chemistry (journal) , computational physics , optics , nuclear physics , irradiation , mathematics , medicine , statistics , chromatography
Purpose To assess the influence of the 106 Rh gamma spectrum on the Monte Carlo simulation of 106 Ru/ 106 Rh ophthalmic plaques, which has been neglected without a quantitative estimation in all previous publications. Methods Simulations were run with the penelope 2014 Monte Carlo code for radiation transport. Depth–dose distributions in water were simulated for the plaque models CCA , CCC , CCX and CIA . In addition to the 106 Rh beta spectrum, all gamma components from the 106 Rh gamma spectrum were included in the simulations. Depth–dose curves were compared with those obtained without considering the 106 Rh gamma spectrum. Moreover, half–value ( HVL ) and tenth–value layers ( TVL ) were estimated for the 106 Rh gamma spectrum in water, PMMA , stainless steel and lead. Some practical radiation protection applications were discussed. Parallel computing was implemented to reduce computing time. Results The contribution of the 106 Rh gamma spectrum on the depth–dose curves is negligible at depths of clinical interest. The HVL and TVL of the 106 Rh gamma spectrum were found to be similar to those of 137 Cs. The air–kerma rate at 1 m for a CCA plaque in typical clinical conditions was about 0.4 μ Gym 2h − 1, resulting in equivalent doses at that point elow 0.05 mS v during a treatment. The air–kerma rate would be underestimated by a factor of 5 if the 106 Rh gamma spectrum were not considered. Also, a freely available software tool was developed to ease parallelization of penelope 2014 simulations that use penmain as steering main program. Conclusions The influence of the 106 Rh gamma spectrum is not relevant for clinical purposes, thus validating the common assumption from the literature. However, for simulations at large distances from the plaques, such as for radiation shielding assessment and estimation of dose to personnel, the gamma spectrum from 106 Rh must be taken into account to obtain accurate results.