Monte Carlo Estimation of Absorbed Dose Distributions Obtained from Heterogeneous 106Ru Eye Plaques

Abstract

Background: The distribution of the emitter substance in ¹⁰⁶Ru eye plaques is usually assumed to be homogeneous for treatment planning purposes. However, this distribution is never homogeneous, and it widely differs from plaque to plaque due to manufacturing factors. Methods: By Monte Carlo simulation of radiation transport, we study the absorbed dose distribution obtained from the specific CCA1364 and CCB1256 ¹⁰⁶Ru plaques, whose actual emitter distributions were measured. The idealized, homogeneous CCA and CCB plaques are also simulated. Results: The largest discrepancy in depth dose distribution observed between the heterogeneous and the homogeneous plaques was 7.9 and 23.7% for the CCA and CCB plaques, respectively. In terms of isodose lines, the line referring to 100% of the reference dose penetrates 0.2 and 1.8 mm deeper in the case of heterogeneous CCA and CCB plaques, respectively, with respect to the homogeneous counterpart. Conclusions: The observed differences in absorbed dose distributions obtained from heterogeneous and homogeneous plaques are clinically irrelevant if the plaques are used with a lateral safety margin of at least 2 mm. However, these differences may be relevant if the plaques are used in eccentric positioning.

Inhomogeneous Surface Dose Distributions of 106Ru Eye Plaques

“…1). As already said by Zaragoza et al [1], 106 Ru eye plaques are very effective for tumors with a tumor thickness of up to 4 mm, and the impact of the inhomogeneous distribution of the 106 Ru eye plaques is negligible. In the case of tumors with tumor thicknesses up to 6 mm, the influence of the inhomogeneous distribution becomes larger.…”

“…This letter is a supplement to the paper of Zaragoza et al [1]. In this publication, the impact of the heterogeneous distribution of the emitter substance of 106 Ru eye plaques on the dose distribution and the treatment planning are exemplarily shown for 2 eye plaques of the CCB and CCA types.…”

“…The investigated CCB-type eye plaque (serial number 1256) shows inhomogeneities in dose distributions of about 25% with respect to the ideal homogenous plaque. As a supplement to [1], 5 other surface dose distributions of the CCB-type eye plaques are shown in this letter (Fig. 1) to illustrate their large variation.…”

“…Thus, at the Technical University of Dortmund, a high-precision dosimetry system was developed, which allows for complete measurements of surface-dose distributions of eye plaques [3,4]. One of these data sets is the basis for the Monte Carlo simulations of inhomogeneous plaques recently shown by Zaragoza et al [1]. Note the large variation of surface-dose distributions measured close to the plaque surface for 5 randomly chosen CCB-type plaques (Fig.…”

Monte Carlo Simulation of the Treatment of Uveal Melanoma Using Measured Heterogeneous ¹⁰⁶Ru Plaques

“…Although some of the most recent works [15, 16] take into consideration the structures at risk, they still assume that the radioactive emitter substance is homogeneously distributed. Finally, Zaragoza et al [20] determined the dose over a water phantom using a fine-grain probability map emission of the emitter substance previously measured over a specific CCA (CCA1364) and a CCB (CCB1256) eye plaque.…”