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Title: Monte Carlo validation of the TrueBeam 10XFFF phase–space files for applications in lung SABR

Purpose: 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{sup 2}. Particular attention was paid to small fields (down to 1 × 1 cm{sup 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{sub ion}) with increasing dose per pulse. MC and ECLIPSE ANISOTROPIC ANALYTICAL ALGORITHM (AAA) calculated PDDs were comparedmore » 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{sup 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{sup 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.« less
Authors:
 [1] ; ; ; ; ;  [2]
  1. Medical Physics, BC Cancer Agency—Centre for the Southern Interior, Kelowna, British Columbia V1Y 5L3 (Canada)
  2. Medical Physics, BC Cancer Agency—Vancouver Centre, Vancouver, British Columbia V5Z 4E6 (Canada)
Publication Date:
OSTI Identifier:
22482422
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 12; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; ALGORITHMS; COMPUTERIZED SIMULATION; DEPTH DOSE DISTRIBUTIONS; DOSEMETERS; FILM DOSIMETRY; IONIZATION CHAMBERS; LINEAR ACCELERATORS; LUNGS; MONTE CARLO METHOD; PHANTOMS; PHOTON BEAMS; RADIATION DOSES; RADIOTHERAPY