title: Testing the methodology for dosimetry audit of heterogeneity corrections and small MLC-shaped fields: Results of IAEA multi-center studies.
abstract: The International Atomic Energy Agency (IAEA) has a long tradition of supporting development of methodologies for national networks providing quality audits in radiotherapy. A series of co-ordinated research projects (CRPs) has been conducted by the IAEA since 1995 assisting national external audit groups developing national audit programs. The CRP 'Development of Quality Audits for Radiotherapy Dosimetry for Complex Treatment Techniques' was conducted in 2009-2012 as an extension of previously developed audit programs.
  
  
  METHODS
  The CRP work described in this paper focused on developing and testing two steps of dosimetry audit: verification of heterogeneity corrections, and treatment planning system (TPS) modeling of small MLC fields, which are important for the initial stages of complex radiation treatments, such as IMRT. The project involved development of a new solid slab phantom with heterogeneities containing special measurement inserts for thermoluminescent dosimeters (TLD) and radiochromic films. The phantom and the audit methodology has been developed at the IAEA and tested in multi-center studies involving the CRP participants.
  
  
  RESULTS
  The results of multi-center testing of methodology for two steps of dosimetry audit show that the design of audit procedures is adequate and the methodology is feasible for meeting the audit objectives. A total of 97% TLD results in heterogeneity situations obtained in the study were within 3% and all results within 5% agreement with the TPS predicted doses. In contrast, only 64% small beam profiles were within 3 mm agreement between the TPS calculated and film measured doses. Film dosimetry results have highlighted some limitations in TPS modeling of small beam profiles in the direction of MLC leave movements.
  
  
  CONCLUSIONS
  Through multi-center testing, any challenges or difficulties in the proposed audit methodology were identified, and the methodology improved. Using the experience of these studies, the participants could incorporate the auditing procedures in their national programs.
authors.affiliation: a International Atomic Energy Agency , Vienna , Austria ;
authors.forename: Joanna
authors.initials: J
authors.lastname: Izewska
authors.affiliation: a International Atomic Energy Agency , Vienna , Austria ;
authors.forename: Paulina
authors.initials: P
authors.lastname: Wesolowska
authors.affiliation: a International Atomic Energy Agency , Vienna , Austria ;
authors.forename: Godfrey
authors.initials: G
authors.lastname: Azangwe
authors.affiliation: b Imaging and Radiation Oncology Core Houston , Houston , Texas , USA ;
authors.forename: David S
authors.initials: DS
authors.lastname: Followill
authors.affiliation: c University of Leeds, St James Hospital , Leeds , UK ;
authors.forename: David I
authors.initials: DI
authors.lastname: Thwaites
authors.affiliation: d Centre De Recherche Nucleaire D'alger , Alger Gare , Algeria ;
authors.forename: Mehenna
authors.initials: M
authors.lastname: Arib
authors.affiliation: e Centro Atomico Ezeiza , Buenos Aires , Argentina ;
authors.forename: Amalia
authors.initials: A
authors.lastname: Stefanic
authors.affiliation: f Instituto Nacional De Cancer , Rio De Janeiro , Brazil ;
authors.forename: Claudio
authors.initials: C
authors.lastname: Viegas
authors.affiliation: g Chinese Centre for Disease Control and Prevention , Beijing , China ;
authors.forename: Luo
authors.initials: L
authors.lastname: Suming
authors.affiliation: h National Radiation Protection Institute , Prague , Czech Republic ;
authors.forename: Daniela
authors.initials: D
authors.lastname: Ekendahl
authors.affiliation: i Maria Sklodowska-Curie Memorial Cancer Centre and Institute of Oncology , Warsaw , Poland ;
authors.forename: Wojciech
authors.initials: W
authors.lastname: Bulski
authors.affiliation: j Medical University of Vienna , Vienna , Austria ;|k Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology , Vienna , Austria.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Georg
mesh_terms: D006801:Humans; D007390:International Agencies; D019047:Phantoms, Imaging; D011786:Quality Control; D000072232:Radiation Dosimeters; D011874:Radiometry / Q000295:instrumentation / Q000379:methods* / Q000592:standards*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards; D013819:Thermoluminescent Dosimetry / Q000295:instrumentation / Q000379:methods / Q000592:standards