Cylindrical Coordinate Based TG-43U1 Parameters for Dose Calculation around Elongated Brachytherapy Sources

Abstract

The applicability of TG-43U1 parameters modified for the cylindrical coordinate system has been investigated for dosimetric evaluation and dose calculations around 1.0cm and 5.0cm long RadioCoil™ ¹⁰³Pd sources.  Dosimetric characteristics of theses sources were calculated in liquid water using the Monte Carlo simulation technique.  To demonstrate the suitability of this methodology, the Monte Carlo simulated dose profiles for a 5.0cm long RadioCoil™ ¹⁰³Pd source at radial distances of 0.5cm, 0.9cm, and 1.25cm were compared with calculated data using TG-43U1 parameters in both polar and cylindrical coordinate systems. In addition, the application of a linear segmented source (LSS) model introduced by Meigooni et al.[JACMP 6, 23-36 (2005)] has also been investigated by using a 1.0cm long source parameterized in cylindrical coordinates.  The results indicate that the TG-43U1 parameters in cylindrical coordinates require less data than the polar coordinate system for dose calculation around elongated brachytherapy sources.  In addition, the LSS model, in conjunction with the cylindrical coordinate based parameters for a 1.0cm long source, can be utilized to replicate the dose distribution around any integral source length. This process will eliminate the need of data collection and entry for multiple source lengths in treatment planning systems.