O58. Illustrated instructions for training of physics QA

Abstract

Introduction Physics QA procedures are typically taught one-to-one, and it can be a challenge to teach large groups of students. Furthermore, it can be difficult for students to remember details when they return to their home institution. We are investigating the use of illustrated instructions for training of physics QA. Here we report on monthly mechanical QA of medical linear accelerators. Materials and methods Illustrated instructions were created for monthly mechanical QA with tolerance tabulated, and underwent several steps of review and refinement. Testers with zero QA experience were then recruited from our radiotherapy department (1 student, 2 computational scientists and 8 dosimetrists). The following parameters were progressively de-calibrated on a Varian C-series linac: Group A = gantry angle, ceiling laser position, X1 jaw position, couch longitudinal position, physical graticule position (5 testers); Group B = Group A + wall laser position, couch lateral and vertical position, collimator angle (3 testers); Group C = Group B + couch angle, wall laser angle, and optical distance indicator (3 testers). Testers were taught how to use the linac, and then used the instructions to try to identify these errors. A physicist observed each session, giving support on machine operation, as necessary. The instructions were further tested with groups of therapists, graduate students and physics residents at multiple institutions. We have also changed the language of the instructions to simulate using the instructions with non-English speakers. Results Testers were able to follow the instructions. They determined gantry, collimator and couch angle errors within 0.4, 0.3, and 0.9 degrees of the actual changed values, respectively. Laser positions were determined within 1 mm, and jaw positions within 2 mm. Couch position errors were determined within 2 and 3 mm for lateral/longitudinal and vertical errors, respectively. Accessory positioning errors were determined within 1 mm. ODI errors were determined within 2 mm when comparing with distance sticks, and 6 mm when using blocks, indicating that distance sticks should be the preferred approach for inexperienced staff. Conclusions Inexperienced users were able to follow these instructions, and catch errors within the criteria suggested by AAPM TG142 for linacs used for IMRT.