A computerized remote table control for fast on-line patient repositioning: implementation and clinical feasibility.

A computerized remote control for a Siemens ZXT treatment couch was implemented and its characteristics were investigated to establish its feasibility for on-line setup corrections, using portal imaging. Communication with the table was obtained by connecting it via a serial line to a work station. The treatment couch enables "goto" commands in the three main directions and around the isocenter. The accuracy of the movements after giving such a command was checked and the time for each movement was recorded. First, the movements into a single direction were studied (range of -4 to +4 cm and -4 degrees to +4 degrees). Each command was repeated four times. Second, the table was moved into the three main directions simultaneously. For this experiment a clinically relevant three-dimensional (3-D) normal distribution of shifts was used [N = 200, standard deviation (SD) 5 mm in the three main directions]. This latter experiment was done twice: without and with rotations (a distribution with SD 1 degrees). During the first experiment, with shifts into one direction, no systematic deviations were found. The overall accuracy of the shifts was 0.6 mm (1 SD) in each direction and 0.04 degrees (1 SD) for the rotations. The time required for a translation ranged between 4 and 13 s and for the rotation between 8 and 20 s. The second experiment with the 3-D distribution of setup errors yielded an error in the 3-D vector length equal to 0.96 mm (1 SD), independent of rotations. Shifts were performed in less than 11 s for 95% of the cases without rotations. When rotations were also performed, 95% of the movements finished in less than 16 s. In conclusion, the table movements are accurate and enable on-line setup corrections in daily clinical practice.