title: Zero field PDD and TMR data for unflattened beams in conventional linacs: A tool for independent dose calculations.
abstract: OBJECTIVE
  To investigate the applicability of the formalism described in BJR supplement n.25 for Flattening Filter Free (FFF) beams in determining the zero-field tissue maximum ratio (TMR) for an independent calculation method of Percentage Depth Doses (PDDs) and relative dose factors (RDFs) at different experimental setups.
  
  
  METHODS
  Experimental PDDs for field size from 40×40cm2to 2×2cm2with Source Surface Distance (SSD) 100cm were acquired. The normalized peak scatter factor for each square field was obtained by fitting experimental RDFs in water and collimator factors (CFs) in air. Maximum log-likelihood methods were used to extract fit parameters in competing models and the Bayesian Information Criterion was used to select the best one. In different experimental setups additional RDFs and TPR1020s for field sizes other than reference field were measured and Monte Carlo simulations of PDDs at SSD 80cm were carried out to validate the results. PDD agreements were evaluated by gamma analysis.
  
  
  RESULTS
  The BJR formalism allowed to predict the PDDs obtained with MC within 2%/2mm at SSD 80cm from 100% down to 50% of the maximum dose. The agreement between experimental TPR1020s and RDFs values at SSD=90cm and BJR calculations were within 1% for field sizes greater than 5×5cm2while it was within 3% for fields down to 2×2cm2.
  
  
  CONCLUSIONS
  BJR formalism can be used for FFF beams to predict PDD and RDF at different SSDs and can be used for independent MU calculations.
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Strolin
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Minosse
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: D'Andrea
authors.affiliation: Azienda Provinciale per i Servizi Sanitari (APSS), Protontherapy Department, Trento, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Fracchiolla
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy.
authors.forename: Vicente
authors.initials: V
authors.lastname: Bruzzaniti
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Luppino
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy.
authors.forename: Marcello
authors.initials: M
authors.lastname: Benassi
authors.affiliation: Medical Physics Laboratory, Regina Elena National Cancer Institute, Via Elio Chianesi 53, 00144 Rome, Italy. Electronic address: lidiastrigari@gmail.com.
authors.forename: Lidia
authors.initials: L
authors.lastname: Strigari
mesh_terms: D016013:Likelihood Functions; D009010:Monte Carlo Method; D010315:Particle Accelerators; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D014867:Water
chemical_list: D014867:Water
keywords: Analytical dose calculation; Flattening Filter Free; Small fields; TPR