title: Customised compensation using intensity modulated beams delivered by dynamic multileaf collimation.
abstract: OBJECTIVE
  This paper describes the development of customised compensation by intensity modulated radiation therapy (IMRT), delivered by dynamic application of a multileaf collimator (MLC), in order to improve dose homogeneity in treatments of the pelvic region. The introduction of this simple IMRT procedure will help facilitate the clinical implementation of more complex 3D conformal therapy techniques.
  
  
  METHODS
  Computer software is used to generate profiles of the intensity modulated beams which are required to deliver a uniform dose in a plane, passing through the isocentre and normal to the beam axis, under an irregular surface contour. These profiles are then operated on by interpreter software which determines the leaf trajectories that are necessary to deliver these beam profiles using a single, unidirectional sweep of the MLC leaves. A full dose calculation based on the calculated leaf positions is subsequently performed, allowing further fine adjustments to the modulation where required.
  
  
  CONCLUSIONS
  The compensation procedure has been successfully tested using films placed under a test phantom. The effect of the compensation procedure on dose distributions in the transverse plane has been investigated using an anthropomorphic phantom. Overall dose homogeneity has been improved through the use of customised compensation delivered by dynamic multileaf collimation.
authors.affiliation: North Western Medical Physics, Christie Hospital NHS Trust, Withington, Manchester, UK.
authors.forename: J H
authors.initials: JH
authors.lastname: Mott
authors.forename: A R
authors.initials: AR
authors.lastname: Hounsell
authors.forename: G J
authors.initials: GJ
authors.lastname: Budgell
authors.forename: J M
authors.initials: JM
authors.lastname: Wilkinson
authors.forename: P C
authors.initials: PC
authors.lastname: Williams
mesh_terms: D006801:Humans; D010388:Pelvis / Q000528:radiation effects; D011879:Radiotherapy Dosage; D011881:Radiotherapy, Computer-Assisted; D012984:Software