title: Four-dimensional radiotherapeutic dose calculation using biomechanical respiratory motion description.
abstract: OBJECTIVE
  Organ motion due to patient breathing introduces a technical challenge for dosimetry and lung tumor treatment by hadron therapy. Accurate dose distribution estimation requires patient-specific information on tumor position, size, and shape as well as information regarding the material density and stopping power of the media along the beam path. A new 4D dosimetry method was developed, which can be coupled to any motion estimation method. As an illustration, the new method was implemented and tested with a biomechanical model and clinical data.
  
  
  METHODS
  First, an anatomical model of the lung and tumor was synthesized with deformable tetrahedral grids using computed tomography (CT) images. The CT attenuation values were estimated at the grid vertices. Respiratory motion was simulated biomechanically based on nonlinear finite element analysis. Contrary to classical image-based methods where motion is described using deformable image registration algorithms, the dose distribution was accumulated over tetrahedral meshes that are deformed using biomechanical modeling based on finite element analysis.
  
  
  RESULTS
  The new method preserves the mass of the objects during simulation with an error between 1.6 and 3.6%. The new method was compared to an existing dose calculation method demonstrating significant differences between the two approaches and overall superior performance using the new method.
  
  
  CONCLUSIONS
  A unified model of 4D radiotherapy respiratory effects was developed where biomechanical simulations are coupled with dose calculations. Promising results demonstrate that this approach has significant potential for the treatment for moving tumors.
authors.affiliation: Laboratoire d'InfoRmatique en Image et Systèmes d'information LIRIS; CNRS UMR 5205, Université Claude Bernard Lyon 1, 69622 , Villeurbanne, France, petru.manescu@liris.cnrs.fr.
authors.forename: Petru
authors.initials: P
authors.lastname: Manescu
authors.forename: Hamid
authors.initials: H
authors.lastname: Ladjal
authors.forename: Joseph
authors.initials: J
authors.lastname: Azencot
authors.forename: Michael
authors.initials: M
authors.lastname: Beuve
authors.forename: Etienne
authors.initials: E
authors.lastname: Testa
authors.forename: Behzad
authors.initials: B
authors.lastname: Shariat
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy*; D009038:Motion; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration