GPU-based fast gamma index calcuation

Xuejun Gu, Xun Jia, Steve B. Jiang
Center for Advanced Radiotherapy Technologies and Department of Radiation Oncology, University of California San Diego, La Jolla, CA 92037-0843
arXiv:1012.1900 [physics.med-ph] (9 Dec 2010)


   author={Gu}, X. and {Jia}, X. and {Jiang}, S.~B.},

   title={“{GPU-based fast gamma index calcuation}”},

   journal={ArXiv e-prints},




   keywords={Physics – Medical Physics},




   adsnote={Provided by the SAO/NASA Astrophysics Data System}


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The gamma-index dose comparison tool has been widely used to compare dose distributions in cancer radiotherapy. The accurate calculation of gamma-index requires an exhaustive search of the closest Euclidean distance in the high-resolution dose-distance space. This is a computational intensive task when dealing with 3D dose distributions. In this work, we combine a geometric method with a radial pre-sorting technique , and implement them on computer graphics processing units (GPUs). The developed GPU-based gamma-index computational tool is evaluated on eight pairs of IMRT dose distributions. The GPU implementation achieved 20x~30x speedup factor compared to CPU implementation and gamma-index calculations can be finished within a few seconds for all 3D testing cases. We further investigated the effect of various factors on both CPU and GPU computation time. The strategy of pre-sorting voxels based on their dose difference values speed up the GPU calculation by about 2-4 times. For n-dimensional dose distributions, gamma-index calculation time on CPU is proportional to the summation of gamma^n over all voxels, while that on GPU is effected by gamma^n distributions and is approximately proportional to the gamma^n summation over all voxels. We found increasing dose distributions resolution leads to quadratic increase of computation time on CPU, while less-than-quadratic increase on GPU. The values of dose difference (DD) and distance-to-agreement (DTA) criteria also have their impact on gamma-index calculation time.
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