SU-E-T-193: Using Truebeam's Research Mode to Automate Mechanical Quality Assurance

To determine the feasibility of automating mechanical quality assurance measurements on the Varian Truebeam LINAC.

Using the XML coding capability of the Varian Truebeam Research Mode, the LINAC was programmed to mimic the beams delivered for the following mechanical tests. These tests included: Field size accuracy, jaw positions for asymmetric fields, collimator rotation isocenter, and MLC positional-accuracy. Images for these beams were acquired with the EPID. The images were analyzed using an analysis code written in MATLAB. Tests for gantry and couch rotation isocenters and radiation and mechanical isocenter coincidence are being developed.

For field-sizes ranging from 4×4cm² to 15×15cm² , the measured matched the nominal field sizes to within 1mm. The collimator rotation isocenter and the overall accuracy for asymmetric field matched to within 1mm. No positional error 〉1mm was seen in the 33 MLC pairs visible in the MLC positional-accuracy images.

A large portion of the time required to make mechanical QA measurements using film is spent placing, processing, and scanning the film. Complete automation in performing these mechanical tests results in a significant time gain compared to film. A majority of the mechanical tests suggested by TG-142 have been performed using this technique, and an automated mechanical QA process has been established in our clinic.