The determination of dose characteristics of ruthenium ophthalmic applicators using radiochromic film

Abstract

Ruthenium ophthalmic applicators are energetic beta ray sources, supplied in several shapes and dimensions, and used in intraocular tumor therapy. Because of their small dimensions, the determination of dosimetric characteristics represents a technical challenge. We developed a semiautomatic method to define surface dose, dose distribution, and percentage depth dose of such applicators using radiochromic dosimetric media. These detectors consist of a thin (7 microns) radiation sensitive layer on polyester base (100 microns total thickness) changing color as a function of radiation exposure. Transmission images of exposed films were then grabbed with a TV-digitizer system to obtain a gray-level image from which dosimetric characteristics such as isodose distribution, dose values, and homogeneity of nuclide distribution were derived. Good agreement between experimental results and Monte Carlo simulation performed using the GEANT 3 code, appear to be a confirmation of the validity of the method. Moreover while manufacturer specifications of absolute and relative dose rates present a standard deviation error of +/- 30% on dose rate and +/- 6% on accuracy of relative dose values, the proposed method reduces the errors to +/- 10% and +/- 4%, respectively.

Calculation of dose distributions for 12 106Ru/106Rh ophthalmic applicator models with the PENELOPE Monte Carlo code

“…Mourtada et al 17 performed a comparative dosimetric analysis of 106 Ru/ 106 Rh ophthalmic brachytherapy and external beam proton therapy. The relative dose distributions for both treatment modalities were calculated in a model eye using the MCNPX MC code for the CCB applicator, yielding contradictory results: the MC-NPX calculations were consistent with the results obtained by Cross et al 16 using MCNP4B and by Taccini et al 9 using GEANT3, whereas the differences found by Cross et al 16 between MCNP4B and ACCEPT 3.0 were similar to those found among MCNPX, ACCEPT 3.0, and Soares et al's 5 film data.…”

“…In the only available study providing dosimetric data on CIB applicators, which was performed by Taccini et al, 9 the authors measured the dose distributions for a number of applicator models using radiochromic film. For the CIB applicator, they reported isodose distributions in a plane perpendicular to the central axis at a 4.5 mm depth.…”

“…13) [in some publications, it is incorrectly stated that the thickness is 0.2 mm (Ref. 9)]. Following the available literature, the radioisotope layer thickness was considered negligible, and the radioisotope was assumed to be uniformly distributed over the active area.…”

“…Several detectors have been used to measure the dose distributions of 106 Ru/ 106 Rh applicators, including diodes, 5 diamond detectors, 5 extrapolation chambers, 5, 6 small volume ionization chambers, 5 polymer gel, 7 thermoluminescent dosimeters, 5,8 alanine detectors, 5 radiochromic films, 5,9 and plastic 5, 10 and liquid 11 scintillators. A good description of the advantages and disadvantages of these detectors for beta dosimetry is provided in ICRU Report 72, 4 which was partially based on the paper by Soares et al, 5 a key reference regarding measurement methods for beta ophthalmic applicators.…”

Current prospects on Low Energy Particle Track Simulation for biomedical applications

“…Comparison at some relevant incident energies of the calculated elastic (IAM-SCAR) and elastic þ rotational (IAM-SCARD) DCS for tetrahydrofuran to experimental results from Milosavljević et al (2005), Allan (2007), Colyer et al (2007 and Dampc et al (2007), theoretical data from Winstead and McKoy (2006), and our recommended values . by other authors with the Monte Carlo codes PENELOPE, MCNP, and GEANT3 (see Sá nchez-Reyes et al, 1998;Cross et al, 2001;Taccini et al, 1997), indicating that the set of CS and the energy loss distribution chosen by us caused a relatively higher energy deposition in greater depths.…”