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

Purpose: Brachytherapy with Ru/ 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 Ru/ Rh plaques used solid phantoms. This work aims to develop a practical method for measuring the absorbed dose distribution in water produced by Ru/ 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 Ru/ Rh plaques.