Open AccessAn analysis of the Arc CHECK ‐ MR diode array's performance for ViewRay quality assurance
Author(s) -
Ellefson Steven T.,
Culberson Wesley S.,
Bednarz Bryan P.,
DeWerd Larry A.,
Bayouth John E.
Publication year - 2017
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/acm2.12107
Subject(s) - quality assurance , inclinometer , arc (geometry) , imaging phantom , diode , current (fluid) , computer science , quality (philosophy) , beam (structure) , optics , physics , mathematics , engineering , optoelectronics , operations management , external quality assessment , cartography , geometry , thermodynamics , geography , quantum mechanics
The Arc CHECK ‐ MR diode array utilizes a correction system with a virtual inclinometer to correct the angular response dependencies of the diodes. However, this correction system cannot be applied to measurements on the ViewRay MR ‐ IGRT system due to the virtual inclinometer's incompatibility with the ViewRay's multiple simultaneous beams. Additionally, the Arc CHECK 's current correction factors were determined without magnetic field effects taken into account. In the course of performing ViewRay IMRT quality assurance with the Arc CHECK , measurements were observed to be consistently higher than the ViewRay TPS predictions. The goals of this study were to quantify the observed discrepancies and test whether applying the current factors improves the Arc CHECK 's accuracy for measurements on the ViewRay. Gamma and frequency analysis were performed on 19 ViewRay patient plans. Ion chamber measurements were performed at a subset of diode locations using a PMMA phantom with the same dimensions as the Arc CHECK . A new method for applying directionally dependent factors utilizing beam information from the ViewRay TPS was developed in order to analyze the current Arc CHECK correction factors. To test the current factors, nine ViewRay plans were altered to be delivered with only a single simultaneous beam and were measured with the Arc CHECK . The current correction factors were applied using both the new and current methods. The new method was also used to apply corrections to the original 19 ViewRay plans. It was found the Arc CHECK systematically reports doses higher than those actually delivered by the ViewRay. Application of the current correction factors by either method did not consistently improve measurement accuracy. As dose deposition and diode response have both been shown to change under the influence of a magnetic field, it can be concluded the current Arc CHECK correction factors are invalid and/or inadequate to correct measurements on the ViewRay system.