title: Monte Carlo simulation of contrast-enhanced whole brain radiotherapy on a CT scanner.
abstract: OBJECTIVE
  To perform a feasibility study of contrast-enhanced whole brain radiotherapy for treating patients with multiple brain metastasis using a conventional computed tomography (CT) scanner.
  
  
  METHODS
  The treatment dose was optimized to be applied in a single run using a maximum tube power of 5200 kWs at 140 kV. CT scans of a large and a small head were used as reference. Irradiation geometry, shielding, axial beam collimation, radial beam collimation, gantry tilt, and tube current for beam modulation were optimized using a Monte Carlo simulation and a contrast agent concentration of 5 mg/ml iodine in the tumor. The statistical uncertainty of the Monte Carlo simulation was corrected using back convolution.
  
  
  RESULTS
  Using a CT tube with a beam collimation of 28.8 mm, a mean tumor dose of 1.76 +/- 0.13 Gy was achieved, while the head bone dose was 2.61 +/- 0.18 Gy with a normal brain dose of 0.98 +/- 0.06 Gy, eye dose of 0.19 +/- 0.05 Gy, and lens dose of 0.15 +/- 0.03 Gy, respectively. Using a CT tube with dose modulation and a beam collimation of 40.0 mm, the mean tumor dose was 2.00 +/- 0.11 Gy with a head bone dose of 1.96 +/- 0.14 Gy, normal brain dose of 1.13 +/- 0.08 Gy, eye dose of 0.21 +/- 0.05 Gy, and lens dose of 0.16 +/- 0.02 Gy, respectively. Thus a standard CT scanner enables an effective tumor dose of 37.0 Gy to be administered in 13 fractions, while exposing healthy brain to an effective dose of 17.2 Gy and head bone to 69.3 Gy. Additional radial collimation implemented in the hardware improves the therapeutic tumor dose by 25.2% in relation to the bone dose.
  
  
  CONCLUSIONS
  Contrast-enhanced total brain radiotherapy is feasible using a conventional CT tube with optimized dose application.
authors.affiliation: Department of Radiotherapy, Charité Medical Center, 13353 Berlin, Germany.
authors.forename: Bernd-Joachim
authors.initials: BJ
authors.lastname: Schultz
authors.forename: Peter
authors.initials: P
authors.lastname: Wust
authors.forename: Lutz
authors.initials: L
authors.lastname: Lüdemann
authors.forename: Gregor
authors.initials: G
authors.lastname: Jost
authors.forename: Hubertus
authors.initials: H
authors.lastname: Pietsch
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary; D003198:Computer Simulation; D003287:Contrast Media; D005123:Eye / Q000528:radiation effects; D006801:Humans; D007455:Iodine; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011835:Radiation Protection; D012886:Skull / Q000528:radiation effects; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media; D007455:Iodine