title: A kernel-based dose calculation algorithm for kV photon beams with explicit handling of energy and material dependencies.
abstract: OBJECTIVE
  Mimicking state-of-the-art patient radiotherapy with high-precision irradiators for small animals is expected to advance the understanding of dose-effect relationships and radiobiology in general. We work on the implementation of intensity-modulated radiotherapy-like irradiation schemes for small animals. As a first step, we present a fast analytical dose calculation algorithm for keV photon beams.
  
  
  METHODS
  We follow a superposition-convolution approach adapted to kV X-rays, based on previous work for microbeam therapy. We assume local energy deposition at the photon interaction point due to the short electron ranges in tissue. This allows us to separate the dose calculation into locally absorbed primary dose and the scatter contribution, calculated in a point kernel approach. We validate our dose model against Geant4 Monte Carlo (MC) simulations and compare the results to Muriplan (XStrahl Ltd, Camberley, UK).
  
  
  RESULTS
  For field sizes of (1 mm)2to (1 cm)2in water, the depth dose curves show a mean disagreement of 1.7% to MC simulations, with the largest deviations in the entrance region (4%) and at large depths (5% at 7 cm). Larger discrepancies are observed at water-to-bone boundaries, in bone and at the beam edges in slab phantoms and a mouse brain. Calculation times are in the order of 5 s for a single beam.
  
  
  CONCLUSIONS
  The algorithm shows good agreement with MC simulations in an initial validation. It has the potential to become an alternative to full MC dose calculation. Advances in knowledge: The presented algorithm demonstrates the potential of kernel-based dose calculation for kV photon beams. It will be valuable in intensity-modulated radiotherapy and inverse treatment planning for high precision small-animal radiotherapy.
authors: Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK.
authors: Anna Merle
authors: AM
authors: Reinhart
authors: Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK.
authors: Martin F
authors: MF
authors: Fast
authors: Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK.
authors: Peter
authors: P
authors: Ziegenhein
authors: Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK.
authors: Simeon
authors: S
authors: Nill
authors: Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK.
authors: Uwe
authors: U
authors: Oelfke
mesh_terms: D000465:Algorithms; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated