title: Measurement of stray radiation within a scanning proton therapy facility: EURADOS WG9 intercomparison exercise of active dosimetry systems.
abstract: OBJECTIVE
  To characterize stray radiation around the target volume in scanning proton therapy and study the performance of active neutron monitors.
  
  
  METHODS
  Working Group 9 of the European Radiation Dosimetry Group (EURADOS WG9-Radiation protection in medicine) carried out a large measurement campaign at the Trento Centro di Protonterapia (Trento, Italy) in order to determine the neutron spectra near the patient using two extended-range Bonner sphere spectrometry (BSS) systems. In addition, the work focused on acknowledging the performance of different commercial active dosimetry systems when measuring neutron ambient dose equivalents, H(∗)(10), at several positions inside (8 positions) and outside (3 positions) the treatment room. Detectors included three TEPCs--tissue equivalent proportional counters (Hawk type from Far West Technology, Inc.) and six rem-counters (WENDI-II, LB 6411, RadEye™ NL, a regular and an extended-range NM2B). Meanwhile, the photon component of stray radiation was deduced from the low-lineal energy transfer part of TEPC spectra or measured using a Thermo Scientific™ FH-40G survey meter. Experiments involved a water tank phantom (60 × 30 × 30 cm(3)) representing the patient that was uniformly irradiated using a 3 mm spot diameter proton pencil beam with 10 cm modulation width, 19.95 cm distal beam range, and 10 × 10 cm(2) field size.
  
  
  RESULTS
  Neutron spectrometry around the target volume showed two main components at the thermal and fast energy ranges. The study also revealed the large dependence of the energy distribution of neutrons, and consequently of out-of-field doses, on the primary beam direction (directional emission of intranuclear cascade neutrons) and energy (spectral composition of secondary neutrons). In addition, neutron mapping within the facility was conducted and showed the highest H(∗)(10) value of ∼ 51 μSv Gy(-1); this was measured at 1.15 m along the beam axis. H(∗)(10) values significantly decreased with distance and angular position with respect to beam axis falling below 2 nSv Gy(-1) at the entrance of the maze, at the door outside the room and below detection limit in the gantry control room, and at an adjacent room (<0.1 nSv Gy(-1)). Finally, the agreement on H(∗)(10) values between all detectors showed a direct dependence on neutron spectra at the measurement position. While conventional rem-counters (LB 6411, RadEye™ NL, NM2-458) underestimated the H(∗)(10) by up to a factor of 4, Hawk TEPCs and the WENDI-II range-extended detector were found to have good performance (within 20%) even at the highest neutron fluence and energy range. Meanwhile, secondary photon dose equivalents were found to be up to five times lower than neutrons; remaining nonetheless of concern to the patient.
  
  
  CONCLUSIONS
  Extended-range BSS, TEPCs, and the WENDI-II enable accurate measurements of stray neutrons while other rem-counters are not appropriate considering the high-energy range of neutrons involved in proton therapy.
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, BP17, Fontenay-aux-Roses 92260, France.
authors.forename: J
authors.initials: J
authors.lastname: Farah
authors.affiliation: Helmholtz Zentrum München, Institute of Radiation Protection, Ingolstädter Landstraße 1, Neuherberg 85764, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Mares
authors.affiliation: Departament de Física, Universitat Autònoma de Barcelona, Bellaterra E-08193, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Romero-Expósito
authors.affiliation: Helmholtz Zentrum München, Institute of Radiation Protection, Ingolstädter Landstraße 1, Neuherberg 85764, Germany and Physik-Department, Technische Universität München, Garching 85748, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Trinkl
authors.affiliation: Departament de Física, Universitat Autònoma de Barcelona, Bellaterra E-08193, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Domingo
authors.affiliation: Czech Technical University in Prague, FNSPE, Břehová 7, Prague 115 19, Czech Republic and National Radiation Protection Institute, Bartoškova 28, Prague 140 00, Czech Republic.
authors.forename: V
authors.initials: V
authors.lastname: Dufek
authors.affiliation: Institute of Nuclear Physics PAN, Radzikowskiego 152, Krakow 31-342, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Klodowska
authors.affiliation: Czech Technical University in Prague, FNSPE, Břehová 7, Prague 115 19, Czech Republic and Department of Radiation Dosimetry, Nuclear Physics Institute, Řež CZ-250 68, Czech Republic.
authors.forename: J
authors.initials: J
authors.lastname: Kubancak
authors.affiliation: Ruđer Bošković Institute, Bijenička c. 54, Zagreb 10000, Croatia.
authors.forename: Ž
authors.initials: Ž
authors.lastname: Knežević
authors.affiliation: Institute of Nuclear Physics PAN, Radzikowskiego 152, Krakow 31-342, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Liszka
authors.affiliation: Ruđer Bošković Institute, Bijenička c. 54, Zagreb 10000, Croatia.
authors.forename: M
authors.initials: M
authors.lastname: Majer
authors.affiliation: Ruđer Bošković Institute, Bijenička c. 54, Zagreb 10000, Croatia.
authors.forename: S
authors.initials: S
authors.lastname: Miljanić
authors.affiliation: Department of Radiation Dosimetry, Nuclear Physics Institute, Řež CZ-250 68, Czech Republic.
authors.forename: O
authors.initials: O
authors.lastname: Ploc
authors.affiliation: Helmholtz Zentrum München, Institute of Radiation Protection, Ingolstädter Landstraße 1, Neuherberg 85764, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Schinner
authors.affiliation: Institute of Nuclear Physics PAN, Radzikowskiego 152, Krakow 31-342, Poland.
authors.forename: L
authors.initials: L
authors.lastname: Stolarczyk
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, BP17, Fontenay-aux-Roses 92260, France.
authors.forename: F
authors.initials: F
authors.lastname: Trompier
authors.affiliation: Helmholtz Zentrum München, Institute of Radiation Protection, Ingolstädter Landstraße 1, Neuherberg 85764, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Wielunski
authors.affiliation: Institute of Nuclear Physics PAN, Radzikowskiego 152, Krakow 31-342, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Olko
authors.affiliation: University of Newcastle upon Tyne, Newcastle upon Tyne, Tyne and Wear NE1 7RU, United Kingdom.
authors.forename: R M
authors.initials: RM
authors.lastname: Harrison
mesh_terms: D005060:Europe; D009502:Neutrons; D019047:Phantoms, Imaging; D017785:Photons; D061766:Proton Therapy / Q000295:instrumentation / Q000379:methods*; D011522:Protons; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D013057:Spectrum Analysis / Q000295:instrumentation / Q000379:methods; D014867:Water
chemical_list: D011522:Protons; D014867:Water