Open AccessOn the need for monitor unit calculations as part of a beam commissioning methodology for a radiation treatment planning system
Author(s) -
Starkschall George,
Steadham Roy E.,
Wells Nathan H.,
O'Neill Laura,
Miller Linda A.,
Rosen Isaac I.
Publication year - 2000
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v1i3.2640
Subject(s) - project commissioning , radiation treatment planning , medical physics , unit (ring theory) , monitor unit , beam (structure) , computer science , nuclear engineering , systems engineering , environmental science , radiation therapy , physics , nuclear medicine , medicine , optics , engineering , mathematics , radiology , publishing , political science , law , mathematics education
This paper illustrates the need for validating the calculation of monitor units as part of the process of commissioning a photon beam model in a radiation treatment planning system. Examples are provided in which this validation identified subtle errors, either in the dose model or in the implementation of the dose algorithm. These errors would not have been detected if the commissioning process only compared relative dose distributions. A set of beam configurations, with varying field sizes, source‐to‐skin distances, wedges, and blocking, were established to validate monitor unit calculations for two different beam models in two different radiation treatment planning systems. Monitor units calculated using the treatment planning systems were compared with monitor units calculated from point dose calculations from tissue‐maximum ratio (TMR) tables. When discrepancies occurred, the dose models and the code were analyzed to identify the causes of the discrepancies. Discrepancies in monitor unit calculations were both significant (up to 5%) and systematic. Analysis of the dose computation software found: (1) a coordinate system transformation error, (2) mishandling of dose‐spread arrays, (3) differences between dose calculations in the commissioning software and the planning software, and (4) shortcomings in modeling of head scatter. Corrections were made in the beam calculation software or in the data sets to overcome these discrepancies. Consequently, we recommend incorporating validation of monitor unit calculations as part of a photon beam commissioning process. PACS number(s): 87.53.–j, 87.66.–a