Drosoula Giantsoudi, Presenter: Nothing to Disclose

Yaxi Liu PhD, Abstract Co-Author: Nothing to Disclose

George Xu PhD, Abstract Co-Author: Nothing to Disclose

Aidnag Zaid Diaz MD, Abstract Co-Author: Nothing to Disclose

Nikos Papanikolaou PhD, Abstract Co-Author: Nothing to Disclose

High accuracy in dose calculations is essential for correct delivery of the prescribed radiation dose to the patient. Commonly used treatment planning systems account for the density of the various human organs but not for their atomic composition, often introducing considerable errors. In this study an accurate calculation and comparison of dose distribution and volume histograms (DVH) was performed for various interstitial brachytherapy sources, using the MCNPX Monte Carlo (MC) simulation code and a human anatomy-based model.

The human anatomy-based model has been developed for MC dose calculations, using transverse color photographic images obtained from the National Library of Medicine’s Visible Human Project. Physical properties such as density and atomic composition are assigned to every voxel (size of 4mm×4mm×4mm) of this model. The MCNPX code was used to simulate particle transport and energy deposited to each voxel of the head part of the reconstructed human anatomy-based model. Three different brachytherapy sources, 252Cf, 137Cs and 192Ir, were simulated as volume sources of 1 mm×10 mm placed in the center of a target volume specified inside the reconstructed head model. Comparisons were performed for calculated planar dose distributions and DVHs from the three brachytherapy sources.

MC calculations revealed significant difference in the maximum dose per initial particle deposited inside the target volume from each source, giving a ratio of 1.00:1.25:1.98 for the 192Ir, 137Cs and 252Cf sources respectively. DVH comparisons for the various sources showed that the mean and minimum doses to the target volume were approximately equal, assuming the same maximum dose delivered at the center of the target volume. Comparing the planar dose distributions from 252Cf and 192Ir sources, gamma index calculation led to gamma values greater than one for 40% of the pixels, using tolerances of 5% dose difference and 4mm distance to agreement. The same comparison between the 192Ir and 137Cs sources resulted in gamma values greater than one for less than 10% of the pixels. The greater discrepancies were found at the lower dose regions (below 70%), while inside the target volume the dose distribution matches well for all three sources.

Dose distribution and DVHs from three different brachytherapy sources were compared in this study. It was observed that the higher the mean energy of the source, such as the 252Cf, the lower the dose gradient, resulting in slightly higher relative dose to the surrounding normal tissues. However, the higher dose per initial particle delivered by this source, while resulting in the same DVH, may lead to a decrease in the duration of treatment of almost 50%, improving patient’s comfort.

Giantsoudi, D, Liu, Y, Xu, G, Diaz, A, Papanikolaou, N, Monte Carlo Dose Calculations for Brachytherapy Sources Based on a Human Anatomy Model.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/7002307.html