title: Secondary radiation dose during high-energy total body irradiation.
abstract: OBJECTIVE
  The goal of this work was to assess the additional dose from secondary neutrons and γ-rays generated during total body irradiation (TBI) using a medical linac X-ray beam.
  
  
  BACKGROUND
  Nuclear reactions that occur in the accelerator construction during emission of high-energy beams in teleradiotherapy are the source of secondary radiation. Induced activity is dependent on the half-lives of the generated radionuclides, whereas neutron flux accompanies the treatment process only.
  
  
  METHODS
  The TBI procedure using a 18 MV beam (Clinac 2100) was considered. Lateral and anterior-posterior/posterior-anterior fractions were investigated during delivery of 2 Gy of therapeutic dose. Neutron and photon flux densities were measured using neutron activation analysis (NAA) and semiconductor spectrometry. The secondary dose was estimated applying the fluence-to-dose conversion coefficients.
  
  
  RESULTS
  The main contribution to the secondary dose is associated with fast neutrons. The main sources of γ-radiation are the following: (56)Mn in the stainless steel and (187)W of the collimation system as well as positron emitters, activated via (n,γ) and (γ,n) processes, respectively. In addition to 12 Gy of therapeutic dose, the patient could receive 57.43 mSv in the studied conditions, including 4.63 μSv from activated radionuclides.
  
  
  CONCLUSIONS
  Neutron dose is mainly influenced by the time of beam emission. However, it is moderated by long source-surface distances (SSD) and application of plexiglass plates covering the patient body during treatment. Secondary radiation gives the whole body a dose, which should be taken into consideration especially when one fraction of irradiation does not cover the whole body at once.
authors.affiliation: Medical Physics Department, Lower Silesian Oncology Center, Hiszfeld Square 12, 53-413, Wroclaw, Poland, janiszewska.m@dco.com.pl.
authors.forename: M
authors.initials: M
authors.lastname: Janiszewska
authors.forename: K
authors.initials: K
authors.lastname: Polaczek-Grelik
authors.forename: M
authors.initials: M
authors.lastname: Raczkowski
authors.forename: B
authors.initials: B
authors.lastname: Szafron
authors.forename: A
authors.initials: A
authors.lastname: Konefał
authors.forename: W
authors.initials: W
authors.lastname: Zipper
mesh_terms: D019583:Dose Fractionation, Radiation; D005214:Fast Neutrons / Q000627:therapeutic use*; D005720:Gamma Rays / Q000627:therapeutic use*; D006283:Health Physics; D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy*; D009501:Neutron Activation Analysis; D011867:Radioisotope Teletherapy / Q000295:instrumentation / Q000379:methods*; D011874:Radiometry; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation / Q000379:methods*; D013057:Spectrum Analysis; D014916:Whole-Body Irradiation / Q000295:instrumentation / Q000379:methods*