Determinação da Distribuição de Dose Absorvida na Água para o Aplicador Oftálmico COC de 106Ru/106Rh Utilizando o Código de Monte Carlo-MCNPX

Abstract

Ophthalmic applicators with source beta 106 Ru / 106 Rh, COC models, are used in the treatment of intraocular tumors near the optic nerve. This type of treatment is very important to know the dose distribution in order to provide the best possible delivery of the prescribed dose to the tumor, preserves the optic nerve extremely critical region, if damaged, can compromise the patient's visual acuity and cause brain sequelae. These dose distributions are complex and doctors controllers only have the source calibration certificate provided by Eckert & Ziegler BEBIG GmbH manufacturer, to realize it. These certificates are limited to 10 display in depth absorbed dose values the water along the central axis of the applicator with the uncertainties of the order of 20% isodose and in a plane located 1 mm from the applicator surface. Thus, it is important to know with more detail and precision dose distributions in water generated by such applicators. For this, we used the Monte Carlo simulation with the use of MCNPX code. Initially be validated by comparing the simulation results to the central axis of the applicator with those provided by the certificate. The different percentages were lower than 5%, validating it in this way, the method used. We calculated the amount of lateral profile to 6 different depths in intervals of 1mm and dose rates in mGy.min-1 for the same depths.

Theoretical estimate of relative depth-doses for the asymmetric and spherical 106Ru/106Rh COC-type plaque used in radiotherapy

“…This plaque contains a cut-out section designed to treat tumors close to the optical nerve, and this asymmetry makes still more harder the dosimetry and may explain the lack of theoretical and experimental dosimetric data on it. The results of dose rates along central axis of the COC plaque obtained by means of the analytical and numerical method described in this work are in a moderate accordance with the unique available MC-MCNPX simulations [2] (maximum difference of -18% at 4 mm depth). And when the results of this work are compared with the data from the manufacturer a maximum difference of -14% at 4 mm depth is found.…”

“…The analytical/numerical calculations of this work disagree with the MC and certificate results by a maximum difference, respectively, of -18% and -14% at 4 mm depth (at a given depth calculated as the difference between our result and the result of ref. [2], relative to the result of ref. [2]).…”

“…[2], relative to the result of ref. [2]). This disagreement may be assigned to the various simplifying hypotheses adopted.…”

“…In Figure 2 is depicted the results of dose rates normalized at 1mm depth plotted against the depth along z-axis, and in order to make a comparison it is also shown the unique available results of MC-MCNPX simulations [2] and data from the manufacturer (taken from [2]). The analytical/numerical calculations of this work disagree with the MC and certificate results by a maximum difference, respectively, of -18% and -14% at 4 mm depth (at a given depth calculated as the difference between our result and the result of ref.…”