title: Clinical use of asymmetric collimators.
abstract: OBJECTIVE
  To illustrate some of the radiation treatment techniques with asymmetric collimators in one field dimension.
  
  
  METHODS
  Treatment planning for various sites is done with an in-house developed treatment planning system. Dose distributions in the central plane are illustrated.
  
  
  RESULTS
  The use of asymmetric collimation, in addition to being a replacement for cerrobend and lead blocks, can facilitate treatment setup with boost fields and with half-beam asymmetric fields as in matching two adjacent fields, in avoiding nearby critical organ or tissue, and in tangential breast treatment. The use of asymmetric collimators would alter the dose distribution across the radiation field and should be accounted for during treatment planning. In conjunction with arc rotation or multiple asymmetric fields, two-dimensional conformal radiotherapy is possible.
  
  
  CONCLUSIONS
  The full potential of asymmetric collimation requires the use of a proper treatment planning algorithm. Some of the treatment techniques with asymmetric collimation in one field dimension are shown here.
authors.affiliation: Department of Physics, University of British Columbia, Vancouver, Canada.
authors.forename: W
authors.initials: W
authors.lastname: Kwa
authors.forename: V
authors.initials: V
authors.lastname: Tsang
authors.forename: R N
authors.initials: RN
authors.lastname: Fairey
authors.forename: S M
authors.initials: SM
authors.lastname: Jackson
authors.forename: E
authors.initials: E
authors.lastname: El-Khatib
authors.forename: R W
authors.initials: RW
authors.lastname: Harrison
authors.forename: S
authors.initials: S
authors.lastname: Kristensen
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy; D010315:Particle Accelerators / Q000295:instrumentation*; D011835:Radiation Protection; D011878:Radiotherapy / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D013679:Technology, Radiologic