title: Accuracy of dose calculation algorithms for static and rotational IMRT of lung cancer: A phantom study.
abstract: OBJECTIVE
  To evaluate the dosimetric accuracy of Pencil beam (PB), Anisotropic Analytical Algorithm (AAA) and Collapsed Cone Convolution Superposition (CCCS) in thoracic tumours for various IMRT techniques.
  
  
  METHODS
  Step-and-shoot Linac IMRT (IMRT), arc volumetric RapidArc (RA) and Helical Tomotherapy (HT) lung treatments for different clinical situations (mediastinum tumour, single metastasis and multiple metastases) were simulated and calculated with PB/AAA, AAA, CCCS, respectively. Delivery quality assurance plans were first verified in homogeneous media (Cheese phantom and ArcCHECK); then several low-density inhomogeneous phantoms were used: the Multiplug ArcCHECK, the commercial ArcCHECK slightly modified with a low density lung-shape insert and a custom-made slab heterogeneous phantom simulating the thorax region. Absolute doses and planar dose maps were checked to assess the agreement between measured and calculated dose distributions.
  
  
  RESULTS
  In total, data referred to 195 point dose measurements and 189 planar measurements were considered. Average point absolute deviations <3% were found for all the delivery techniques/dose algorithms. In small targets completely embedded in very low density media, deviations up to 7-10% and 4-5% were found for PB and AAA/CCCS respectively. Excellent results were found for planar measurements in ArcCHECK configurations, where ≥ 95% of points satisfy the 3%/3 mm acceptance criteria for all the algorithms.
  
  
  CONCLUSIONS
  A satisfactory agreement (<2%) between planned and measured doses was generally found for CCCS and AAA, excepting the very critical situation of a small tumour completely embedded in air. A significant dose overestimation (from few to 5-7%) was confirmed for PB in complex inhomogeneous arrangements.
authors: Medical Physics Department, IRCCS San Raffaele, Milano, Italy.
authors: Carla
authors: C
authors: Sini
authors: Medical Physics Department, IRCCS San Raffaele, Milano, Italy. Electronic address: broggi.sara@hsr.it.
authors: Sara
authors: S
authors: Broggi
authors: Medical Physics Department, IRCCS San Raffaele, Milano, Italy.
authors: Claudio
authors: C
authors: Fiorino
authors: Medical Physics Department, IRCCS San Raffaele, Milano, Italy.
authors: Giovanni Mauro
authors: GM
authors: Cattaneo
authors: Medical Physics Department, IRCCS San Raffaele, Milano, Italy.
authors: Riccardo
authors: R
authors: Calandrino
mesh_terms: D000465:Algorithms; D008175:Lung Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation*; D012399:Rotation
keywords: Dose calculation algorithms; IMRT techniques; Low density media