Oral & Poster Presentation – Physics Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2016

Abstract number 3

Monte Carlo in the assessment of the effects of tissue composition on dose distributions in low dose rate prostate brachytherapy 

Leydon P* 
*The Galway Clinic, Galway, Ireland 

AIMS/INTRODUCTION: The method outlined in the AAPM TG-43 report was the gold standard for calculation of doses in brachytherapy for many years and is still used in many clinical treatment planning software packages. The TG-43 calculation makes several assumptions in order to simplify the more complex reality, such as assuming all tissues are equivalent to water. The purpose of this study was to investigate the differences in dose distributions of Low Dose Rate (LDR) Prostate Brachytherapy I125 sources due to tissue composition/heterogeneity against the TG-43 method. 

MATERIALS/METHODS: Several models, each consisting of 79 individual I125 sources in a clinical arrangement were simulated using Monte Carlo techniques with PENELOPE/penEasy code. The system is capable of simulation of x-ray transport in various materials/tissues at a range of energies including those used for LDR brachytherapy. 

The geometry and energy spectrum of individual seeds was based on the Oncura 6711 model, and the simulated dose distributions were acquired in a 5cc sphere of water/tissue material. The elemental composition of simulated tissues was based on ICRP reports (1975&2002), and the work of Woodard and White (1986). 

All simulations were conducted using an off the shelf laptop computer with 1.8GHz processor and 6GB of RAM. 

RESULTS: The results of the simulations demonstrated observable differences in dose distributions between the TG-43 water based model, and the other more realistic tissue models using various tissues compositions. Heterogeneous tissues containing simulated calcifications also demonstrated differences in dose distributions, the magnitude of which depended on factors such as calcification size, location and composition. 

CONCLUSION: Future work will include validation of the Monte Carlo seed models against TG-43, inclusion of more particle histories, and the development of more accurate voxel based anatomical phantom models. This will allow for a robust quantitative analysis of simulation results and more thorough assessment of the differences observed.