Absorbed dose distributions from ophthalmic 106 Ru/106 Rh plaques measured in water with radiochromic film.

ABSTRACT

PURPOSE: Brachytherapy with 106 Ru/106 Rh plaques offers good outcomes for small-to-medium choroidal melanomas and retinoblastomas. The dose measurement of the plaques is challenging, due to the small range of the emitted beta particles and steep dose gradients involved. The scarce publications on film dosimetry of 106 Ru/106 Rh plaques used solid phantoms. This work aims to develop a practical method for measuring the absorbed dose distribution in water produced by 106 Ru/106 Rh plaques using EBT3 radiochromic film. METHODS: Experimental setups were developed to determine the dose distribution at a plane perpendicular to the symmetry axis of the plaque and at a plane containing the symmetry axis. One CCA and two CCX plaques were studied. The dose maps were obtained with the FilmQA Pro 2015 software, using the triple-channel dosimetry method. The measured dose distributions were compared to published Monte Carlo simulation and experimental data. RESULTS: A good agreement was found between measurements and simulations, improving upon published data. Measured reference dose rates agreed within the experimental uncertainty with data obtained by the manufacturer using a scintillation detector, with typical differences below 5%. The attained experimental uncertainty was 4.1% (k = 1) for the perpendicular setup, and 7.9% (k = 1) for the parallel setup. These values are similar or smaller than those obtained by the manufacturer and other authors, without the need of solid phantoms that are not available to most users. CONCLUSIONS: The proposed method may be useful to the users to perform quality assurance preclinical tests of 106 Ru/106 Rh plaques.