Abstract
BackgroundThe automated and integrated machine performance check (MPC) tool was verified against independent detectors to evaluate its beam uniformity and output detection abilities to consider it suitable for daily quality assurance (QA).MethodsMeasurements were carried out on six linear accelerators (each located at six individual sites) using clinically available photon and electron energies for a period up to 12 months (n = 350). Daily constancy checks on beam symmetry and output were compared against independent devices such as the SNC Daily QA 3, PTW Farmer ionization chamber, and SNC field size QA phantom. MPC uniformity detection of beam symmetry adjustments was also assessed. Sensitivity of symmetry and output measurements were assessed using statistical process control (SPC) methods to derive tolerances for daily machine QA and baseline resets to account for drifts in output readings. I‐charts were used to evaluate systematic and nonsystematic trends to improve error detection capabilities based on calculated upper and lower control levels (UCL/LCL) derived using standard deviations from the mean dataset.ResultsThis study investigated the vendor's method of uniformity detection. Calculated mean uniformity variations were within ± 0.5% of Daily QA 3 vertical symmetry measurements. Mean MPC output variations were within ± 1.5% of Daily QA 3 and ±0.5% of Farmer ionization chamber detected variations. SPC calculated UCL values were a measure of change observed in the output detected for both MPC and Daily QA 3.ConclusionsMachine performance check was verified as a daily quality assurance tool to check machine output and symmetry while assessing against an independent detector on a weekly basis. MPC output detection can be improved by regular SPC‐based trend analysis to measure drifts in the inherent device and control systematic and random variations thereby increasing confidence in its capabilities as a QA device. A 3‐monthly MPC calibration assessment was recommended based on SPC capability and acceptability calculations.
Highlights
With increasing complexity in radiotherapy treatment delivery and automated treatment checks, quality assurance (QA) guidelines require significant updates to include evidence‐based tolerances for optimal machine performance
Machine performance check daily uniformity variations from baselines were compared to symmetry variations measured using Daily QA 3 and SNC Field Size (FS)‐QA system devices
In the case of machine E, it was observed that vertical Daily QA 3 symmetry variations were within 0.4 ± 0.1% of its corresponding machine performance check (MPC) uniformity
Summary
With increasing complexity in radiotherapy treatment delivery and automated treatment checks, quality assurance (QA) guidelines require significant updates to include evidence‐based tolerances for optimal machine performance. The use of relative baseline comparisons of detector readings obtained during commissioning of a linear accelerator may not be sufficient or practical on a daily basis as QA checks are performed by treatment operators using cross‐calibrated detectors These sophisticated and newly developed cross‐calibrated detector properties can vary significantly with radiation type, amount of exposure, dose rate, detector sensitivity, type of detector material, etc.[1,5]. QA guidelines are clear about recommended tests for newer treatment techniques such as volumetric modulated arc therapy and stereotactic ablative/body radiotherapy SABR/SBRT instead there are no recommendations based on statistical process control (SPC) methods on the frequency of use and tolerance for the newly added and automated daily QA systems on linear accelerators. The automated and integrated machine performance check (MPC) tool was verified against independent detectors to evaluate its beam uniformity and output detection abilities to consider it suitable for daily quality assurance (QA). A 3‐monthly MPC calibration assessment was recommended based on SPC capability and acceptability calculations
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