title: Technical Report: Reference photon dosimetry data for Varian accelerators based on IROC-Houston site visit data.
abstract: OBJECTIVE
  Accurate data regarding linear accelerator (Linac) radiation characteristics are important for treatment planning system modeling as well as regular quality assurance of the machine. The Imaging and Radiation Oncology Core-Houston (IROC-H) has measured the dosimetric characteristics of numerous machines through their on-site dosimetry review protocols. Photon data are presented and can be used as a secondary check of acquired values, as a means to verify commissioning a new machine, or in preparation for an IROC-H site visit.
  
  
  METHODS
  Photon data from IROC-H on-site reviews from 2000 to 2014 were compiled and analyzed. Specifically, data from approximately 500 Varian machines were analyzed. Each dataset consisted of point measurements of several dosimetric parameters at various locations in a water phantom to assess the percentage depth dose, jaw output factors, multileaf collimator small field output factors, off-axis factors, and wedge factors. The data were analyzed by energy and parameter, with similarly performing machine models being assimilated into classes. Common statistical metrics are presented for each machine class. Measurement data were compared against other reference data where applicable.
  
  
  RESULTS
  Distributions of the parameter data were shown to be robust and derive from a student's t distribution. Based on statistical and clinical criteria, all machine models were able to be classified into two or three classes for each energy, except for 6 MV for which there were eight classes. Quantitative analysis of the measurements for 6, 10, 15, and 18 MV photon beams is presented for each parameter; supplementary material has also been made available which contains further statistical information.
  
  
  CONCLUSIONS
  IROC-H has collected numerous data on Varian Linacs and the results of photon measurements from the past 15 years are presented. The data can be used as a comparison check of a physicist's acquired values. Acquired values that are well outside the expected distribution should be verified by the physicist to identify whether the measurements are valid. Comparison of values to this reference data provides a redundant check to help prevent gross dosimetric treatment errors.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030; Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030; and Graduate School of Biomedical Sciences, The University of Texas Health Science Center-Houston, Houston, Texas 77030.
authors.forename: James R
authors.initials: JR
authors.lastname: Kerns
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030; Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030; and Graduate School of Biomedical Sciences, The University of Texas Health Science Center-Houston, Houston, Texas 77030.
authors.forename: David S
authors.initials: DS
authors.lastname: Followill
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Jessica
authors.initials: J
authors.lastname: Lowenstein
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Andrea
authors.initials: A
authors.lastname: Molineu
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Paola
authors.initials: P
authors.lastname: Alvarez
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Paige A
authors.initials: PA
authors.lastname: Taylor
authors.affiliation: Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
authors.forename: Francesco C
authors.initials: FC
authors.lastname: Stingo
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030; Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030; and Graduate School of Biomedical Sciences, The University of Texas Health Science Center-Houston, Houston, Texas 77030.
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Kry
mesh_terms: D010315:Particle Accelerators / Q000295:instrumentation* / Q000706:statistics & numerical data; D017785:Photons; D011874:Radiometry / Q000295:instrumentation* / Q000706:statistics & numerical data; D012016:Reference Values; D014867:Water
chemical_list: D014867:Water