Cylindrical coordinate-based TG-43U1 parameters for dose calculation around elongated brachytherapy sources

In 2001, the use of cylindrical coordinates was demonstrated to be more suitable than was the use of polar coordinates for accurate computer calculations during treatment planning for ¹⁹²Ir intravascular brachytherapy sources. In the present work, we investigated the applicability of cylindrical coordinate-based TG-43U1 parameters for dosimetric evaluation and dose calculations for RadioCoil ¹⁰³Pd sources (RadioMed Corporation, Tyngsboro, MA) 1.0-cm to 6.0-cm long. For brevity, only the results for sources 1.0-cm, 3.0-cm, and 5.0-cm. long are presented here. Dosimetric characteristics of RadioCoil ¹⁰³Pd 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 RadioCoil ¹⁰³Pd source 5.0-cm long at radial distances of 0.5 cm, 0.9 cm, and 1.25 cm were compared with calculated data using TG-43U1 parameters in the polar and cylindrical coordinate systems. In addition, we also used a source 1.0-cm long parameterized using cylindrical coordinates to investigate the application of a linear segmented source (LSS) model originally introduced by our group. The results indicate that, for dose calculation around elongated brachytherapy sources, cylindrical coordinate-based TG-43U1 parameters more accurately represent the dose distribution around an elongated source than the polar coordinate-based parameters. In addition, the LSS model, in conjunction with the cylindrical coordinate-based parameters for a source 1.0-cm long, can be used to replicate the dose distribution around any integral source length. This process eliminates the need to collect and enter data for multiple source lengths into treatment planning systems.