title: A convolution-superposition dose calculation engine for GPUs.
abstract: OBJECTIVE
  Graphic processing units (GPUs) are increasingly used for scientific applications, where their parallel architecture and unprecedented computing power density can be exploited to accelerate calculations. In this paper, a new GPU implementation of a convolution/superposition (CS) algorithm is presented.
  
  
  METHODS
  This new GPU implementation has been designed from the ground-up to use the graphics card's strengths and to avoid its weaknesses. The CS GPU algorithm takes into account beam hardening, off-axis softening, kernel tilting, and relies heavily on raytracing through patient imaging data. Implementation details are reported as well as a multi-GPU solution.
  
  
  RESULTS
  An overall single-GPU acceleration factor of 908x was achieved when compared to a nonoptimized version of the CS algorithm implemented in PlanUNC in single threaded central processing unit (CPU) mode, resulting in approximatively 2.8 s per beam for a 3D dose computation on a 0.4 cm grid. A comparison to an established commercial system leads to an acceleration factor of approximately 29x or 0.58 versus 16.6 s per beam in single threaded mode. An acceleration factor of 46x has been obtained for the total energy released per mass (TERMA) calculation and a 943x acceleration factor for the CS calculation compared to PlanUNC. Dose distributions also have been obtained for a simple water-lung phantom to verify that the implementation gives accurate results.
  
  
  CONCLUSIONS
  These results suggest that GPUs are an attractive solution for radiation therapy applications and that careful design, taking the GPU architecture into account, is critical in obtaining significant acceleration factors. These results potentially can have a significant impact on complex dose delivery techniques requiring intensive dose calculations such as intensity-modulated radiation therapy (IMRT) and arc therapy. They also are relevant for adaptive radiation therapy where dose results must be obtained rapidly.
authors.affiliation: Département de génie informatique et génie logiciel, Ecole polytechnique de Montréal, 2500 Chemin de Polytechnique, Montréal, Québec H3T 1J4, Canada. sami.hissoiny@polymtl.ca
authors.forename: Sami
authors.initials: S
authors.lastname: Hissoiny
authors.forename: Benoît
authors.initials: B
authors.lastname: Ozell
authors.forename: Philippe
authors.initials: P
authors.lastname: Després
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D019544:Equipment Failure Analysis; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*