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Program Information

Development of a MCNP Based Monte Carlo Dose Calculation Program for Brachytherapy

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H Jiang

H Jiang1*, (1) Univ Kansas Medical Center, Kansas City, KS


MO-RAM-GePD-TT-1 (Monday, July 31, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Theater

Purpose: Often in brachytherapy treatment planning, tissue heterogeneity is ignored and patient body is treated as water equivalent. This approximation is acceptable most of time. However, in cases with extreme heterogeneity, e.g. use of air balloon applicators, meaningful dose deviations might occur. The goal of this project is to develop a MC program to provide more accurate brachytherapy dose calculations.

Methods: MCNP is accepted to be versatile, reliable, and powerful. The source code of MCNP is available to end users upon approval. To develop a MC code, starting from a well benchmarked program would save tremendous effort and time. Several major modifications to MCNP included: first, a new method for importing CT data was developed. With original MCNP, CT voxels have to be placed in a repeated structure defined in the MCNP input file. The input file is huge in size, and the initialization process takes long time for geometry check. The new method takes a binary file as input and removes geometry check for CT structure. Second, a new way to dynamically define material density was introduced. The curve of electron density versus Hounsfield number (HN) was integrated, and only several tissue materials were specified in input file. During simulations, when a particle reaches to a CT voxel, the corresponding HN would lead to correct density assignment. Third, a method allowing geometry overlap was added to enable placement of a source structure in a CT structure.

Results: The new code was used to re-calculate HDR treatment plans. Only planning CT, iridium seed dwelling positions, and times were necessary as inputs.

Conclusion: The feasibility of a revised MCNP code for HDR dose calculations was demonstrated. The computational time could be minutes. The code served as a useful tool to examine the accuracy of commercial treatment planning systems.

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