Open AccessIdentification of a potential source of error for 6FFF beams delivered on an Agility TM multileaf collimator
Author(s) -
Lorenz Friedlieb H.,
Paris Matthew I.
Publication year - 2021
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 - 10.1002/acm2.13212
Subject(s) - isocenter , multileaf collimator , quality assurance , collimator , monitor unit , computer science , bridging (networking) , linear particle accelerator , optics , materials science , beam (structure) , nuclear medicine , physics , engineering , medicine , computer network , operations management , external quality assessment , imaging phantom
Purpose The performance of the Agility TM multileaf collimator was investigated with a focus on dynamic, small fields for flattening filter free (FFF) beams. Methods In this study we have developed a simple tool to test the robustness of the control mechanisms during dynamic beam delivery for Elekta’s VersaHD linear accelerator with Integrity 4.0.4 control software. We have programed the planning system to calculate dose for delivery of sweeping gaps. These sweeping gaps have a constant speed, constant size, and are delivered at a constant dose rate. Therefore they specifically identify delivery problems in dynamic mode. Results The Elekta Agility TM control mechanism fails to maintain accurate delivery for small, dynamic sweeping gaps. For small gap sizes, the Agility TM control mechanism delivers a field that is more than four times the size of the planned field width without generating an interlock. This has dosimetric implications: The discrepancy between calculated and measured doses increases with decreasing gap size and exceeds 10% and 60% at isocenter for a 3.5 mm and 1 mm gap size, respectively. Conclusion A deficiency of the Agility TM control system was identified in this study. This deficiency is a potential source of error for volumetric modulated arc therapy fields and could therefore contribute to relatively high failure rates in quality assurance measurements, especially for FFF beams.