Purpose: Quality assurance (QA) of complex linear accelerators is critical and highly time consuming. Varian’s Machine Performance Check (MPC) uses IsoCal phantom to test geometric and dosimetric aspects of the TrueBeam systems in <5min. In this study we independently tested the accuracy and robustness of the MPC tools. Methods: MPC is automated for simultaneous image‐acquisition, using kV‐and‐MV onboard‐imagers (EPIDs), while delivering kV‐and‐MV beams in a set routine of varying gantry, collimator and couch angles. MPC software‐tools analyze the images to test: i) beam‐output and uniformity, ii) positional accuracy of isocenter, EPIDs, collimating jaws (CJs), MLC leaves and couch and iii) rotational accuracy of gantry, collimator and couch. 6MV‐beam dose‐output and uniformity were tested using ionization‐chamber (IC) and ICarray. Winston‐Lutz‐Tests (WLT) were performed to measure isocenter‐offsets caused by gantry, collimator and couch rotations. Positional accuracy of EPIDs was evaluated using radio‐opaque markers of the IsoCal phantom. Furthermore, to test the robustness of the MPC tools we purposefully miscalibrated a non‐clinical TrueBeam by introducing errors in beam‐output, energy, symmetry, gantry angle, couch translations, CJs and MLC leaves positions. Results: 6MV‐output and uniformity were within ±0.6% for most measurements with a maximum deviation of ±1.0%. Average isocenter‐offset caused by gantry and collimator rotations was 0.316±0.011mm agreeing with IsoLock (0.274mm) and WLT (0.41mm). Average rotation‐induced couch‐shift from MPC was 0.378±0.032mm agreeing with WLT (0.35mm). MV‐and‐kV imager‐offsets measured by MPC were within ±0.15mm. MPC predicted all machine miscalibrations within acceptable clinical tolerance. MPC detected the output miscalibrations within ±0.61% while the MLC and couch positions were within ±0.06mm and ±0.14mm, respectively. Gantry angle miscalibrations were detected within ±0.1°. Conclusions: MPC is a useful tool for QA of TrueBeam systems and its automation makes it highly efficient for testing both geometric and dosimetric aspects of the machine. This is very important for hypo‐fractionated SBRT treatments. Received support from Varian Medical Systems, Palo Alto, CA 94304‐1038.

It has been advocated by health care leaders that incident learning systems are important for error prevention and process improvement in the radiation therapy (RT). We have designed a web-based system for reporting any individual events in RT and clinical implemented in 2007. The goal of this study is to quantify the impact of a large-volume, department-wide incidental learning system on patient safety and process improvements. Materials/Methods: Over a ten-year period, our clinic practice was encouraged to voluntary report any occurrence that could have or had resulted in a deviation including events with low risk deviations and the events which have no impact on patients but which could provide a better process. The spectrum of reported events extended from minor workflow issues (e.g. scheduling or disruption of workflow, etc) to errors in treatment delivery. In addition to event reporting, the learning system also includes accolade reporting (e.g. reporting of someone doing something nice or helping to improve patient care) to build a strong organization culture. A multidisciplinary committee was assigned to review the reported events biweekly and to facilitate proactive measures (e.g. develop new process or procedures) to improve the patient safety and process or workflow. The ten-year data were retrospectively analyzed and mapped to RT process to determine in which workflow step(s) events are likely to occur and/or first to be discovered. Results: Between 2008 and 2017, a total of 13,786 events including 420 accolades were reported. 128 (<1%) events were reported as severe risks. The overall incident rate per 1000 patients has reduced over time. In most sub processes, the incident rates have significant reduced since 2012 after several interventions were introduced. For examples, the occurrence of incomplete or wrong MD orders has decreased from 104 to 0 from 2012 to 2017; the reported incidence on planning and plan preparation issues by dosimetrists reduced by 75% and the missing treatment approval by physicists reduced by 50%; the software and hardware related issues have been reduced by 70%. We have found that physicist chart review, therapist (both treatment and simulation) chart review, dosimetry planning, and physics weekly chart check are the four most important processes to identity the safety and process issues. Among the 13,876 events, 1,021 incidents were related to staff communication issues. Conclusion: Our data demonstrate that effective implementation and use of an incident learning system can successfully encourage reporting of incidents. Event reporting and accolades serve as a proactive means to improve safety, workflow and organization culture. We have also identified that communication issues among therapists, dosimetrists, physicists and physicians is one of the largest root causes for the incidents in a large RT department.

Purpose: According to TG‐40 percent‐depth‐dose (PDD) tolerance is ±2% but TG‐142 is ±1%. Now the question is, which one is relevant in IMRT era? The primary objective of this study is to evaluate dosimetric impact of beam‐energy‐drifts on IMRT‐delivery. Methods: Beam‐energy drifts were simulated by adjusting Linac's bending‐magnet‐current (BMC) followed by tuning the pulse‐forming network and adjusting gun‐current. PDD change of −0.6% and +1.2% were tested. Planar‐dosimetry measurements were performed using an ionization‐chamber‐array in solid‐water phantoms. Study includes 10‐head‐and‐neck and 3‐breast cancer patients. en‐face beam‐deliveries were also tested at 1.3cm and 5.3cm depths. Composite and single‐field dose‐distributions were compared against the plans to determine %Gamma pass‐rates (%GPRs). For plan dose comparisons, changes in %Gamma pass‐rates (cPGPRs) were computed/reported to exclude the differences between dose‐computation and delivery. Dose distributions of the drifted‐energies were compared against their baseline measurements to determine the% GPRs. A Gamma criteria of 3%/3mm was considered for plan‐dose comparisons while 3%/1mm used for measured dose intercomparisons. Results: For composite‐dose delivery, average cPGPRs were 0.41%±2.48% and −2.54%±3.65% for low‐energy (LE) and high‐energy (HE) drifts, respectively. For measured dose inter‐comparisons, the average%GPRs were 98.4%±2.2% (LE‐drift) and 95.8%±4.0 (HE‐drift). The average %GPR of 92.6%±4.3% was noted for the worst‐case scenario comparing LE‐drift to HE‐drift. All en‐face beams at 5.3 cm depth have cPGPRs within ±4% of the baseline‐energy measurements. However, greater variations were noted for 1.3cm depth. Average %GPRs for drifted energies were >99% at 5.3cm and >97% at 1.3cm depths. However, for the worst‐case scenario (LE‐drift to HE‐drift) these numbers dropped to 95.2% at 5.3cm and 93.1% at 1.3cm depths. Conclusion: The dosimetric impact of beam‐energy drifts was found to be within clinically acceptable tolerance. However, this study includes a single energy with limited range of PDD change. Further studies are on going and the results will be presented. Received funding from Varian Medical Systems, Palo Alto, CA

We proposed a novel approach that uses the kV flat panel detector available on linac for x-ray generator test. This approach eliminates the inefficiencies and variability associated with using third-party QA detectors while enabling an automated process.