Abstract
In prostate cancer treatment, there is an increasing interest in the permanent radioactive seeds implant technique. Currently, in Brazil, the seeds are imported with high prices, which prohibit their use in public hospitals. A ceramic matrix that can be used as a radioisotope carrier and radiographic marker was developed at our institution. The ceramic matrix is distinguished by the characteristic of maintaining the radioactive material uniformly distributed in its surface. In this work, Monte Carlo simulations were performed in order to assess the dose distributions generated by this prototype seed model, with the ceramic matrix encapsulated in titanium, in the same way as the commercial 6711 seed. The obtained data was assessed, as described in the TG‐43U1 report by the American Association of Physicists in Medicine, for two seed models: (1) the most used model 6711 source — for validation and comparison, and (2) for the prototype model with the ceramic matrix. The dosimetric parameters dose rate constant, Λ, radial dose function, gL(r), and anisotropy function, F(r,θ), were derived from simulations by the Monte Carlo method using the MCNP5 code. A Λ 0.992 (±2.33%) cGyh−1U−1 was found for the prototype model. In comparison with the 6711 model, a lower dose fall‐off on transverse axis was found, as well as a lower dose anisotropy for the radius r= 0.25 cm. In general, for all distances, the prototype seed model presents a slightly larger anisotropy between 0° ≤ Θ < 50° and anisotropy similar to the 6711 model for Θ ≥ 50°. The dosimetric characteristics of the prototype model presented in this study suggest that its use is feasible. Because of the model's characteristics, seeds of lower specific activity iodine might be necessary which, on the other hand, would help to reduce costs. However, it has to be emphasized that the proposed source is a prototype, and the required (AAPM prerequisites) experimental study and tolerance manufacturer values are pending for future studies.PACS numbers: 87.53.Jw, 87.55.K
Highlights
75 Paixão et al.: Monte Carlo Study of a New I-125 Brachytherapy Prototype Seedradioisotopes: 125I, 103Pd and 131Cs.[4]
Several seed models exist on the market,(5-6) but they all share three main physical characteristics: a radioisotope used for treatment, an encapsulation material, and a radiopaque material for imaging visualization.[7]. Several studies have been made to improve the dosimetric characteristics of the available seeds,(7-14) and new designs and materials have been used in new seed models.[15,16,17,18] Currently, in Brazil, permanent implants with 125I seeds — the only seed model used in our country is the 6711 — are performed by a few medical institutions, mostly private ones, and the seeds are imported with high prices, which prohibits their use in public hospitals
The purpose of this work is to characterize the dose distribution of a prototype seed model that has a ceramic matrix as a radioisotope carrier and a radiographic marker encapsulated in titanium, in the same way as the commercial 6711 seed, using the dose calculation described in the TG43U1 report by the American Association of Physicists in Medicine (AAPM).(5) The dosimetric parameters dose rate constant, Λ, radial dose function, gL(r), and anisotropy function, F(r,θ), were derived from simulations using the Monte Carlo code Monte Carlo N-Particle code version 5 (MCNP5)
Summary
75 Paixão et al.: Monte Carlo Study of a New I-125 Brachytherapy Prototype Seedradioisotopes: 125I, 103Pd and 131Cs.[4]. In order to reduce the financial cost of this treatment modality and to improve the dosimetric characteristics of the existing seeds, it is of great importance to have a national technology. A ceramic matrix that can be used as a radioisotope carrier and radiographic marker was developed at Nuclear Technology Development Center (CDTN) of the National Commission of Nuclear Energy (CNEN). The purpose of this work is to characterize the dose distribution of a prototype seed model that has a ceramic matrix as a radioisotope carrier and a radiographic marker encapsulated in titanium, in the same way as the commercial 6711 seed, using the dose calculation described in the TG43U1 report by the American Association of Physicists in Medicine (AAPM).(5) The dosimetric parameters dose rate constant, Λ, radial dose function, gL(r), and anisotropy function, F(r,θ), were derived from simulations using the Monte Carlo code MCNP5
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