title: Derivation of angular separation to obtain beam edge coincidence in tangential fields.
abstract: The separation of the two gantry angles in a pair of tangential fields required to obtain posterior beam edge coincidence is derived. This derivation enables one to calculate the second gantry angle at the time of simulation. Experience has shown that the setup angle is within 1 degree of the calculated value.
authors.affiliation: BC Cancer Agency, Victoria, Canada.
authors.forename: F S
authors.initials: FS
authors.lastname: Chen
authors.forename: J
authors.initials: J
authors.lastname: Scrimger
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy*; D003198:Computer Simulation; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted; D013679:Technology, Radiologic