ROPES eye plaque brachytherapy dosimetry for two models of 103Pd seeds

Abstract

Brachytherapy dose distributions are calculated for 15 mm ROPES eye plaque loaded with model Theragenics200 and IR06-(103)Pd seeds. The effects of stainless steel backing and Acrylic insert on dose distribution along the central axis of the eye plaque and at critical ocular structure are investigated. Monte Carlo simulation was carried out with the Version 5 of the MCNP. The dose at critical ocular structure by considering the eye composition was calculated. Results are compared with the calculated data for COMS eye plaque loaded with Theragenics200 palladium-103 seeds and model 6711 iodine-125 seed. The air kerma strength of the IR06-(103)Pd seed to deliver 85 Gy in apex of tumor in water medium was calculated to be 4.10 U/seed. Along the central axis of stainless steel plaque loaded with new (103)Pd seeds in Acrylic insert, the dose reduction relative to water is 6.9% at 5 mm (apex). Removal of the Acrylic insert from the plaque (replacing with water) did not make significantly difference in dose reduction results (~0.2%). The presence of the stainless steel backing results in dose enhancement near the plaque relative to water. Doses at points of interest are higher for ROPES eye plaque when compared to COMS eye plaque. The dosimetric parameters calculated in this work for the new palladium seed, showed that in dosimetry point of view, the IR06-(103)Pd seed is suitable for use in brachytherapy. The effect of Acrylic insert on dose distribution is negligible and the main effect on dose reduction is due to the presence of stainless steel plaque backing.

I‐125 ROPES eye plaque dosimetry: Validation of a commercial 3D ophthalmic brachytherapy treatment planning system and independent dose calculation software with GafChromic® EBT3 films

“…Saidi et al 16 found a depth dependent dose correction factor in their Monte Carlo study of two models of Pd-103 seeds in a 15 mm diameter ROPES plaque. A reduction of 4% due to the stainless steel backing was observed at 2 mm depth, and this reduction increased to approximately 9% at 5 mm depth.…”

“…EBT3 film measurements without the stainless steel backing have been shown to agree with full dose to water calculations, indicating that the acrylic seed carrier has a negligible effect on the dose compared to a full dose to water assumption. Granero et al 17 and Saidi et al 16 have performed Monte Carlo simulations of the 15 mm diameter ROPES plaque, both with and without the acrylic seed carrier to assess its effect on the dose distribution. It was also found in these studies that the acrylic carrier had a negligible effect on the dose distribution.…”

“…Radiation Oncology Physics and Engineering Services, Australia (ROPES) type eye plaques, however, consist of a stainless steel backing (density = 7.912 g/cm 3 ) and an acrylic seed carrier insert (density 1.069 g/cm 3 , Z eff = 6.5). 16 For both the COMS and ROPES plaques the seed insert has a radius of curvature of ∼12 mm in order to conform to the external sclera and offset the seeds by 1 mm from the sclera. Due to differences in atomic number and density of materials used in the construction of the ROPES and COMS type eye plaques, the effect of these materials on the dose distributions produced by the plaques is expected to be dissimilar.…”

“…1,8,13,14 To date, one group has published a Monte Carlo study of the dose distributions produced by ROPES type eye plaques with model 6711 I-125 seeds, 17 and another using two models of Pd-103 seeds. 16 Granero et al 17 performed Monte Carlo simulations both with and without the acrylic seed carrier to assess its effect on the dose distribution for the 15 mm diameter ROPES plaque. Saidi et al 16 also performed Monte Carlo simulations of the 15 mm diameter ROPES plaque.…”

“…16 Granero et al 17 performed Monte Carlo simulations both with and without the acrylic seed carrier to assess its effect on the dose distribution for the 15 mm diameter ROPES plaque. Saidi et al 16 also performed Monte Carlo simulations of the 15 mm diameter ROPES plaque. Using version 5 of MCNP, the effect of the stainless steel backing and acrylic carrier on the dose distributions produced by plaques loaded with Ther-agenics200 and IR06 Pd-103 seeds was assessed.…”