Contributing Editor: Ray Ryan, Vice President of Sales, East Coast Metrology
East Coast Metrology (ECM) has a client who requires a special rectangular X-Ray fixture to be placed at the center of their imaging room to calibrate the position of the X-Rays relative to the treatment beam. Originally, each time the client wanted the X-Ray system checked for alignment, the fixture would need to be measured and moved accordingly until it was centered accurately. This required the measurement of 3 planes, construction of intersecting geometry, building a reference frame from the geometry and finally computing the corrections. The process was iterative and very time consuming since the positioning tolerance was very tight (+/- 0.1 mm).
ECM and Brunson worked together to develop a targeting scheme using ½ inch, threaded SMR nests that could be placed on the X-Ray fixture to allow direct measurement and the use of a software watch window that allowed a laser tracker technician to measure at least 3 points to set the fixture within tolerance relative to a nominal value. Using this approach greatly simplified the process and reduced the time to position the fixture by 80%. Additionally, the fixture geometric features were not made to exacting standards, so the legacy process wasn’t completely repeatable. Using the SMR nests proved to be highly repeatable and thus improved X-Ray alignment results.