Session Item

Since the installation of the SGRT-system AlignRT by VisionRT at the “Strahlenzentrum Hamburg MVZ” there is a unique possibility to evaluate the patient movement during the treatments, and the therapy as a whole. Furthermore, the stereoscopic x-ray cameras of the CyberKnife (CK) allow a comparison between three different systems (AlignRT, CBCT, CK cam) with qualitative conclusions about the accuracy of the patient positioning.

This analysis uses finished treatments of the pelvic region of 40 patients per system independently of their prescriptions. The evaluation comprises all treatments as a whole, and is focused on the three translation dimensions: superior-inferior, left-right, and anterior-posterior.

The mean deviation over all fractions per system is within a millimetre tolerance (sigma_CK(lng/lat/vrt) = 0.83/0.2/0.32; sigma_CB(lng/lat/vrt) = 0.04/0.03/0.01; sigma_SGRT(lng/lat/vrt) = 1.3/0.6/1.0; all in mm). These qualities of accuracy are displayed with the magnitude of the deviations in all the three dimensions mag = √(lng²+lat²+vrt²); mag_CK = 0.91mm, mag_CB = 0.05, mag_SGRT = 1.75.

The combination of SGRT and CBCT is a benefit for the gold standard CBCT since the SGRT assures the CT positioning during the treatment within a 2mm tolerance. It also supports less frequent CBCTs to reduce the radiation load. The influence of the bladder and rectum on the anterior patient surface, as well as possible abdominal motion, has yet to be investigated further. The camera system accuracy of the CyberKnife is between the accuracies of the CBCT and the SGRT. Therefore, it benefits from a constant tracking on bony structures or fiducials during the treatment, and is probably the best choice for its purpose of a low number and a long duration of fractions compared to the conventional linacs.