title: Changes to dose in the build-up region when using multi-leaf collimators in place of lead blocks supported on an accessory tray.
abstract: Doses in the build-up region have been compared for regular fields with and without a perspex accessory tray and for two irregular fields defined by either a Philips multi-leaf collimator (MLC) or lead blocks. The results show an increase in doses within the build-up region, by up to a factor of two, primarily due to the presence of the accessory tray. Fields shaped with the MLC exhibited build-up characteristics similar to those in unblocked fields and hence there will be systematic changes to the build-up dose when treatments are transferred from lead blocking techniques to those using an MLC mounted within the treatment head.
authors: North Western Medical Physics Department, Christie Hospital, Manchester, UK.
authors: E J
authors: EJ
authors: Adams
authors: A R
authors: AR
authors: Hounsell
mesh_terms: D006801:Humans; D007854:Lead; D008953:Models, Anatomic; D011834:Radiation Monitoring / Q000295:instrumentation; D011835:Radiation Protection / Q000295:instrumentation*; D011855:Radiodermatitis / Q000209:etiology / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation*
chemical_list: D007854:Lead