title: Influence of beam incidence and irradiation parameters on stray neutron doses to healthy organs of pediatric patients treated for an intracranial tumor with passive scattering proton therapy.
abstract: OBJECTIVE
  In scattering proton therapy, the beam incidence, i.e. the patient's orientation with respect to the beam axis, can significantly influence stray neutron doses although it is almost not documented in the literature.
  
  
  METHODS
  MCNPX calculations were carried out to estimate stray neutron doses to 25 healthy organs of a 10-year-old female phantom treated for an intracranial tumor. Two beam incidences were considered in this article, namely a superior (SUP) field and a right lateral (RLAT) field. For both fields, a parametric study was performed varying proton beam energy, modulation width, collimator aperture and thickness, compensator thickness and air gap size.
  
  
  RESULTS
  Using a standard beam line configuration for a craniopharyngioma treatment, neutron absorbed doses per therapeutic dose of 63μGyGy(-1) and 149μGyGy(-1) were found at the heart for the SUP and the RLAT fields, respectively. This dose discrepancy was explained by the different patient's orientations leading to changes in the distance between organs and the final collimator where external neutrons are mainly produced. Moreover, investigations on neutron spectral fluence at the heart showed that the number of neutrons was 2.5times higher for the RLAT field compared against the SUP field. Finally, the influence of some irradiation parameters on neutron doses was found to be different according to the beam incidence.
  
  
  CONCLUSIONS
  Beam incidence was thus found to induce large variations in stray neutron doses, proving that this parameter could be optimized to enhance the radiation protection of the patient.
authors.affiliation: IRSN - Institut de Radioprotection et de Sûreté Nucléaire, Service de Dosimétrie Externe BP17, 92262 Fontenay-aux-Roses Cedex, France. Electronic address: anthony.bonfrate@irsn.fr.
authors.forename: A
authors.initials: A
authors.lastname: Bonfrate
authors.affiliation: IRSN - Institut de Radioprotection et de Sûreté Nucléaire, Service de Dosimétrie Externe BP17, 92262 Fontenay-aux-Roses Cedex, France. Electronic address: jad.farah@irsn.fr.
authors.forename: J
authors.initials: J
authors.lastname: Farah
authors.affiliation: Institut Curie - Centre de Protonthérapie d'Orsay (CPO) - Campus universitaire bâtiment 101, 91898 Orsay, France.
authors.forename: L
authors.initials: L
authors.lastname: De Marzi
authors.affiliation: Institut Curie - Centre de Protonthérapie d'Orsay (CPO) - Campus universitaire bâtiment 101, 91898 Orsay, France.
authors.forename: S
authors.initials: S
authors.lastname: Delacroix
authors.affiliation: Centre Antoine Lacassagne (CAL) - Cyclotron biomédical, 227 avenue de la Lanterne, 06200 Nice, France.
authors.forename: J
authors.initials: J
authors.lastname: Hérault
authors.affiliation: IRSN - Institut de Radioprotection et de Sûreté Nucléaire, Service de Dosimétrie Externe BP17, 92262 Fontenay-aux-Roses Cedex, France.
authors.forename: R
authors.initials: R
authors.lastname: Sayah
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institute of Health, Rockville, MD 20850, USA.
authors.forename: C
authors.initials: C
authors.lastname: Lee
authors.affiliation: J Crayton Pruitt Family Departments of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA.
authors.forename: W E
authors.initials: WE
authors.lastname: Bolch
authors.affiliation: IRSN - Institut de Radioprotection et de Sûreté Nucléaire, Service de Dosimétrie Externe BP17, 92262 Fontenay-aux-Roses Cedex, France.
authors.forename: I
authors.initials: I
authors.lastname: Clairand
mesh_terms: D002648:Child; D003397:Craniopharyngioma / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D009502:Neutrons; D019047:Phantoms, Imaging; D010911:Pituitary Neoplasms / Q000532:radiotherapy*; D061766:Proton Therapy / Q000295:instrumentation* / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods
keywords: Beam incidence; Intracranial treatments; Proton therapy; Stray neutron doses