The potential of semi-analytical dose calculation algorithms for low energy brachytherapy

International Conference on Medical Physics

August 03-05, 2015 Birmingham, UK

Kyveli Zourari, Manos Zoros, Eleftherios Pappas, Evaggelos Pantelis, Pantelis Karaiskos and Panagiotis Papagiannis

Posters-Accepted Abstracts: J Nucl Med Radiat Ther

Abstract :

Recently dose calculation algorithms accounting for inhomogeneities are actively explored in brachytherapy. While Monte Carlo simulation has been proposed as a time efficient alternative for accurate doseimetry in low energy brachytherapy, semianalytical models that are simple and do not exhibit statistical uncertainty could be equally accurate for specidic applications. This work reports on the accuracy of a Sievert type semi-analytical dose calculation model for single 125I source dosimetry. Monte Carlo simulation was used to score the scatter dose distribution of a point source in various tissue materials to arrive at a function of scatter to primary dose ratio versus distance. Simulations were also performed around a commercially available source to characterize the anisotropy of the scatter dose distribution and obtain data for benchmarking purposes. The dose rate per unit air kerma strength distribution around the commercially available source was calculated as the superposition of the contribution by a number of point sources uniformly distributed within the source, using the above data with a simple ray tracing algorithm and narrow beam attenuation coefficients weighted by the initially emitted 125I energy spectrum. Resuts were found in good agreement with corresponding Monte Carlo results. The semi-analytical model can be easily customized to different source models and materials and could prove useful in dosimetry for low energy prostate brachytherapy provided that material segmentation form patient imaging is achievable with limited uncertainty in the future, and that uncertainty due to its inherent 1D pathlength character is abated by the increased number of seed sources implanted.