title: Dosimetric characterization of small fields using a plastic scintillator detector: A large multicenter study.
abstract: OBJECTIVE
  In modern radiation therapy accurate small fields dosimetry is a challenge and its standardization is fundamental to harmonize delivered dose in different institutions. This study presents a multicenter characterization of MLC-defined small field for Elekta and Varian linear accelerators. Measurements were performed using the Exradin W1 plastic scintillator detector.
  
  
  METHODS
  The project enrolled 24 Italian centers. Each center performed Tissue Phantom Ratio (TPR), in-plane and cross-plane dose profiles of 0.8×0.8cm2field, and Output Factor (OF) measurements for square field sizes ranging from 0.8 to 10cm. Set-up conditions were 10cm depth in water phantom at SSD 90cm. Measurements were performed using two twin Exradin W1 plastic scintillator detectors (PSD) correcting for the Cerenkov effect as proposed by the manufacturer.
  
  
  RESULTS
  Data analysis from 12 Varian and 12 Elekta centers was performed. Measurements of 7 centers were not included due to cable problems. TPR measurements showed standard deviations (SD)<1%; SD<0.4mm for the profile penumbra was obtained, while FWHM measurements showed SD<0.5mm. OF measurements showed SD<1.5% for field size greater than 2×2cm2. Median OFs values were in agreement with the recent bibliography.
  
  
  CONCLUSIONS
  High degree of consistency was registered for all the considered parameters. This work confirmed the importance of multicenter dosimetric intercomparison. W1 PSD could be considered as a good candidate for small field measurements.
authors.affiliation: Medical Physics Unit of Radiation Oncology Dept., Humanitas Research Hospital, Milano, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Mancosu
authors.affiliation: A.O. Ordine Mauriziano di Torino, Torino, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Pasquino
authors.affiliation: Medical Physics Unit of Radiation Oncology Dept., Humanitas Research Hospital, Milano, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Reggiori
authors.affiliation: Department of Medical Physics and Radiation Oncology, IFCA, I-50139 Firenze, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Masi
authors.affiliation: Medical Physics Unit, Azienda USL Toscana Centro, Firenze, I-50012 Firenze, Italy. Electronic address: serenella.russo@aslcentro.toscana.it.
authors.forename: Serenella
authors.initials: S
authors.lastname: Russo
authors.affiliation: A.O. Ordine Mauriziano di Torino, Torino, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Stasi
mesh_terms: D010315:Particle Accelerators; D019047:Phantoms, Imaging; D010969:Plastics; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation* / Q000592:standards*
chemical_list: D010969:Plastics
keywords: Multicenter intercomparison; Plastic scintillator detector; Small field output factor