title: Lowering whole-body radiation doses in pediatric intensity-modulated radiotherapy through the use of unflattened photon beams.
abstract: OBJECTIVE
  Intensity modulated radiotherapy (IMRT) has been linked with an increased risk of secondary cancer induction due to the extra leakage radiation associated with delivery of these techniques. Removal of the flattening filter offers a simple way of reducing head leakage, and it may be possible to generate equivalent IMRT plans and to deliver these on a standard linear accelerator operating in unflattened mode.
  
  
  METHODS
  An Elekta Precise linear accelerator has been commissioned to operate in both conventional and unflattened modes (energy matched at 6 MV) and a direct comparison made between the treatment planning and delivery of pediatric intracranial treatments using both approaches. These plans have been evaluated and delivered to an anthropomorphic phantom.
  
  
  RESULTS
  Plans generated in unflattened mode are clinically identical to those for conventional IMRT but can be delivered with greatly reduced leakage radiation. Measurements in an anthropomorphic phantom at clinically relevant positions including the thyroid, lung, ovaries, and testes show an average reduction in peripheral doses of 23.7%, 29.9%, 64.9%, and 70.0%, respectively, for identical plan delivery compared to conventional IMRT.
  
  
  CONCLUSIONS
  IMRT delivery in unflattened mode removes an unwanted and unnecessary source of scatter from the treatment head and lowers leakage doses by up to 70%, thereby reducing the risk of radiation-induced second cancers. Removal of the flattening filter is recommended for IMRT treatments.
authors.affiliation: University Hospital Birmingham, Edgbaston, Birmingham, UK. Jason.cashmore@uhb.nhs.uk
authors.forename: Jason
authors.initials: J
authors.lastname: Cashmore
authors.forename: Mark
authors.initials: M
authors.lastname: Ramtohul
authors.forename: Dan
authors.initials: D
authors.lastname: Ford
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D002648:Child; D005374:Filtration / Q000295:instrumentation; D006801:Humans; D009381:Neoplasms, Radiation-Induced / Q000517:prevention & control*; D058958:Organs at Risk; D010315:Particle Accelerators / Q000295:instrumentation*; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012542:Scattering, Radiation; D014916:Whole-Body Irradiation / Q000379:methods*