title: Monte Carlo validation of the TrueBeam 10XFFF phase-space files for applications in lung SABR.
abstract: OBJECTIVE
  To establish the clinical acceptability of universal Monte Carlo phase-space data for the 10XFFF (flattening filter free) photon beam on the Varian TrueBeam Linac, including previously unreported data for small fields, output factors, and inhomogeneous media. The study was particularly aimed at confirming the suitability for use in simulations of lung stereotactic ablative radiotherapy treatment plans.
  
  
  METHODS
  Monte Carlo calculated percent depth doses (PDDs), transverse profiles, and output factors for the TrueBeam 10 MV FFF beam using generic phase-space data that have been released by the Varian MC research team were compared with in-house measurements and published data from multiple institutions (ten Linacs from eight different institutions). BEAMnrc was used to create field size specific phase-spaces located underneath the jaws. Doses were calculated with DOSXYZnrc in a water phantom for fields ranging from 1 × 1 to 40 × 40 cm(2). Particular attention was paid to small fields (down to 1 × 1 cm(2)) and dose per pulse effects on dosimeter response for high dose rate 10XFFF beams. Ion chamber measurements were corrected for changes in ion collection efficiency (P(ion)) with increasing dose per pulse. MC and ECLIPSE ANISOTROPIC ANALYTICAL ALGORITHM (AAA) calculated PDDs were compared to Gafchromic film measurement in inhomogeneous media (water, bone, lung).
  
  
  RESULTS
  Measured data from all machines agreed with Monte Carlo simulations within 1.0% and 1.5% for PDDs and in-field transverse profiles, respectively, for field sizes >1 × 1 cm(2) in a homogeneous water phantom. Agreements in the 80%-20% penumbra widths were better than 2 mm for all the fields that were compared. For all the field sizes considered, the agreement between their measured and calculated output factors was within 1.1%. Monte Carlo results for dose to water at water/bone, bone/lung, and lung/water interfaces as well as within lung agree with film measurements to within 2.8% for 10 × 10 and 3 × 3 cm(2) field sizes. This represents a significant improvement over the performance of the ECLIPSE AAA.
  
  
  CONCLUSIONS
  The 10XFFF phase-space data offered by the Varian Monte Carlo research team have been validated for clinical use using measured, interinstitutional beam data in water and with film dosimetry in inhomogeneous media.
authors.affiliation: Medical Physics, BC Cancer Agency-Centre for the Southern Interior, Kelowna, British Columbia V1Y 5L3, Canada.
authors.forename: Tony
authors.initials: T
authors.lastname: Teke
authors.affiliation: Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia V5Z 4E6, Canada.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Duzenli
authors.affiliation: Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia V5Z 4E6, Canada.
authors.forename: Alanah
authors.initials: A
authors.lastname: Bergman
authors.affiliation: Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia V5Z 4E6, Canada.
authors.forename: Francis
authors.initials: F
authors.lastname: Viel
authors.affiliation: Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia V5Z 4E6, Canada.
authors.forename: Parmveer
authors.initials: P
authors.lastname: Atwal
authors.affiliation: Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia V5Z 4E6, Canada.
authors.forename: Ermias
authors.initials: E
authors.lastname: Gete
mesh_terms: D000465:Algorithms; D001842:Bone and Bones / Q000528:radiation effects; D003198:Computer Simulation; D006801:Humans; D008168:Lung / Q000528:radiation effects / Q000601:surgery*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D011874:Radiometry; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014867:Water
chemical_list: D014867:Water