title: Measurement of stray neutron doses inside the treatment room from a proton pencil beam scanning system.
abstract: OBJECTIVE
  To measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil beam scanning (PBS) technique.
  
  
  METHODS
  Measurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100-220MeV), field sizes ((2×2)-(20×20)cm2) and modulation widths (0-15cm).
  
  
  RESULTS
  For pristine proton peak irradiations, large variations of neutron H∗(10)/D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H∗(10)/D for pristine proton pencil beams varied between 0.04μSvGy-1at beam energy 100MeV and a (2×2)cm2field at 2.25m distance and 90° angle with respect to the beam axis, and 72.3μSvGy-1at beam energy 200MeV and a (20×20) cm2field at 1m distance along the beam axis.
  
  
  CONCLUSIONS
  The obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters.
authors.affiliation: Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN), Radzikowskiego 152, 31-342 Krakow, Poland.
authors.forename: N
authors.initials: N
authors.lastname: Mojżeszek
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, BP-17, 92260 Fontenay-aux-Roses, France; Hôpitaux Universitaires Paris-Sud, Pôle Imagerie et Médecine Nucléaire, Hôpital du Kremlin-Bicêtre, 78 Rue Général Leclerc, 94270 Le Kremlin-Bicêtre, France(1). Electronic address: jad.farah@hotmail.fr.
authors.forename: J
authors.initials: J
authors.lastname: Farah
authors.affiliation: Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN), Radzikowskiego 152, 31-342 Krakow, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Kłodowska
authors.affiliation: Nuclear Physics Institute, Academy of Sciences of the Czech Republic (NPI), CZ-250 68 Řež, Czech Republic.
authors.forename: O
authors.initials: O
authors.lastname: Ploc
authors.affiliation: Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN), Radzikowskiego 152, 31-342 Krakow, Poland.
authors.forename: L
authors.initials: L
authors.lastname: Stolarczyk
authors.affiliation: Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN), Radzikowskiego 152, 31-342 Krakow, Poland; Centre od Oncology, Kraków Division, PL-31-115 Kraków, Poland.
authors.forename: M P R
authors.initials: MP
authors.lastname: Waligórski
authors.affiliation: Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN), Radzikowskiego 152, 31-342 Krakow, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Olko
mesh_terms: D009010:Monte Carlo Method; D009502:Neutrons / Q000627:therapeutic use*; D019047:Phantoms, Imaging; D061766:Proton Therapy; D011829:Radiation Dosage; D011874:Radiometry; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation
keywords: Out-of-field doses; Pencil beam scanning systems; Proton therapy; Secondary neutrons; Stray neutron doses; TEPC