Brachytherapy
Volume 8, Issue 3 , Pages 318-323, July 2009

A quantitative three-dimensional dose attenuation analysis around Fletcher-Suit-Delclos due to stainless steel tube for high-dose-rate brachytherapy by Monte Carlo calculations

Department of Radiation Oncology, University of Toledo Health Science Campus, Toledo, OH

Received 26 September 2007; received in revised form 25 March 2008; accepted 25 November 2008. published online 17 February 2009.

Abstract 

Purpose

The commercially available brachytherapy treatment-planning systems today, usually neglects the attenuation effect from stainless steel (SS) tube when Fletcher-Suit-Delclos (FSD) is used in treatment of cervical and endometrial cancers. This could lead to potential inaccuracies in computing dwell times and dose distribution. A more accurate analysis quantifying the level of attenuation for high-dose-rate (HDR) iridium 192 radionuclide (192Ir) source is presented through Monte Carlo simulation verified by measurement.

Methods and Materials

In this investigation a general Monte Carlo N-Particles (MCNP) transport code was used to construct a typical geometry of FSD through simulation and compare the doses delivered to point A in Manchester System with and without the SS tubing. A quantitative assessment of inaccuracies in delivered dose vs. the computed dose is presented. In addition, this investigation expanded to examine the attenuation-corrected radial and anisotropy dose functions in a form parallel to the updated AAPM Task Group No. 43 Report (AAPM TG-43) formalism. This will delineate quantitatively the inaccuracies in dose distributions in three-dimensional space. The changes in dose deposition and distribution caused by increased attenuation coefficient resulted from presence of SS are quantified using MCNP Monte Carlo simulations in coupled photon/electron transport. The source geometry was that of the Vari Source wire model VS2000. The FSD was that of the Varian medical system. In this model, the bending angles of tandem and colpostats are 15° and 120°, respectively. We assigned 10 dwell positions to the tandem and 4 dwell positions to right and left colpostats or ovoids to represent a typical treatment case. Typical dose delivered to point A was determined according to Manchester dosimetry system.

Results and Conclusions

Based on our computations, the reduction of dose to point A was shown to be at least 3%. So this effect presented by SS–FSD systems on patient dose is of concern.

Keywords: FSD applicator, Attenuation, Brachytherapy, Monte Carlo simulation

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 This paper was presented at the AAPM 2006 annual meeting; Med Phys. 2006;33:2060.

PII: S1538-4721(08)00705-8

doi:10.1016/j.brachy.2008.11.012

Brachytherapy
Volume 8, Issue 3 , Pages 318-323, July 2009

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