title: Configuration and validation of an analytical model predicting secondary neutron radiation in proton therapy using Monte Carlo simulations and experimental measurements.
abstract: OBJECTIVE
  This study focuses on the configuration and validation of an analytical model predicting leakage neutron doses in proton therapy.
  
  
  METHODS
  Using Monte Carlo (MC) calculations, a facility-specific analytical model was built to reproduce out-of-field neutron doses while separately accounting for the contribution of intra-nuclear cascade, evaporation, epithermal and thermal neutrons. This model was first trained to reproduce in-water neutron absorbed doses and in-air neutron ambient dose equivalents, H*(10), calculated using MCNPX. Its capacity in predicting out-of-field doses at any position not involved in the training phase was also checked. The model was next expanded to enable a full 3D mapping of H*(10) inside the treatment room, tested in a clinically relevant configuration and finally consolidated with experimental measurements.
  
  
  RESULTS
  Following the literature approach, the work first proved that it is possible to build a facility-specific analytical model that efficiently reproduces in-water neutron doses and in-air H*(10) values with a maximum difference less than 25%. In addition, the analytical model succeeded in predicting out-of-field neutron doses in the lateral and vertical direction. Testing the analytical model in clinical configurations proved the need to separate the contribution of internal and external neutrons. The impact of modulation width on stray neutrons was found to be easily adjustable while beam collimation remains a challenging issue. Finally, the model performance agreed with experimental measurements with satisfactory results considering measurement and simulation uncertainties.
  
  
  CONCLUSIONS
  Analytical models represent a promising solution that substitutes for time-consuming MC calculations when assessing doses to healthy organs.
authors: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, External Dosimetry Department, BP17, 92260 Fontenay-aux-Roses, France. Electronic address: jad.farah@irsn.fr.
authors: J
authors: J
authors: Farah
authors: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, External Dosimetry Department, BP17, 92260 Fontenay-aux-Roses, France.
authors: A
authors: A
authors: Bonfrate
authors: Institut Curie - Centre de Protonthérapie d'Orsay (CPO), Campus Universitaire Bâtiment 101, 91898 Orsay, France.
authors: L
authors: L
authors: De Marzi
authors: Institut Curie - Centre de Protonthérapie d'Orsay (CPO), Campus Universitaire Bâtiment 101, 91898 Orsay, France.
authors: A
authors: A
authors: De Oliveira
authors: Institut Curie - Centre de Protonthérapie d'Orsay (CPO), Campus Universitaire Bâtiment 101, 91898 Orsay, France.
authors: S
authors: S
authors: Delacroix
authors: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, External Dosimetry Department, BP17, 92260 Fontenay-aux-Roses, France.
authors: F
authors: F
authors: Martinetti
authors: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, External Dosimetry Department, BP17, 92260 Fontenay-aux-Roses, France.
authors: F
authors: F
authors: Trompier
authors: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Pôle Radioprotection de l'Homme, External Dosimetry Department, BP17, 92260 Fontenay-aux-Roses, France.
authors: I
authors: I
authors: Clairand
mesh_terms: D006801:Humans; D008962:Models, Theoretical; D009010:Monte Carlo Method; D009502:Neutrons; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation
keywords: Analytical models; Monte Carlo simulations; Proton therapy; Stray neutrons