title: Checking monitor unit calculations using coordinate transformations to calculate off-axis distances in the collimator frame of reference.
abstract: An important part of treatment-planning QA is to check Monitor Units (MUs) calculated by treatment-planning programs. This is generally straightforward, unless the central axis is blocked. One way to check MUs in this case is to select a reference point in the open portion of the field and use the off-axis distance (OAD), as well as other relevant data, to verify the dose. If wedges are employed in the treatment, the OAD must be specified in the collimator frame-of-reference because one must know where the calculation point is with respect to the wedge to calculate the dose correctly. The purpose of this paper is to describe a method of calculating the OAD in the collimator frame-of-reference using the system of coordinate transformations described by Siddon
authors.affiliation: Department of Radiation Oncology, University of California San Francisco, San Francisco, California 94143, USA.
authors.forename: Paula L
authors.initials: PL
authors.lastname: Petti
mesh_terms: D001703:Biophysics / Q000379:methods; D015233:Models, Statistical; D011786:Quality Control; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*