Measuring system for testing the mechanical isocenter accuracy of medical linear accelerators

Abstract

A system for measuring the accuracy of the mechanical isocenter of linear accelerators is presented. Experimental equipment as well as software for recording the inaccuracies in the position of the rotational axes of the gantry, collimator and treatment table were developed and tested at the Institute of Oncology Ljubljana. For each of the axis, two dimensional shifts were calculated in order to minimize the uncertainty of the position as much as possible without moving the linear accelerator or treatment table. For a particular linear accelerator we found that the position of the three axes can be improved significantly. After corrections, the positions of the rotational axes of the gantry, collimator and treatment table were within circles of radius: 0.07 mm, 0.10 mm and 0.23 mm, with the uncertainty of 0.06 mm (k = 1 SD). These data confirm that our linear accelerator is mechanically suitable also for stereotactic radiosurgery.