Purpose: Rotating gamma ray systems have been developed for stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (SRT). Different designs are available commercially that differ in the source number, source dimensions, and source distribution/arrangement. In this study, we investigated two designs with regard to their capabilities and dosimetric parameters for SRS/SRT.
Methods: The CybeRay system (OUR United RT Group, Xian, China) consists of a ring gantry containing 13 Co-60 sources focusing at the isocenter with 7 changeable collimators. The treatment head can also swing 35° in the superior direction. Galaxy RTi (Akesis, Concord, CA) contains 30 Co-60 sources, which can rotate as a group creating 30 non-overlapping arcs. It includes 4 changeable collimators. Both systems are equipped with inline cone beam CT for real-time image guidance, which share the same isocenter with the treatment beams. Ten previous patients treated on the GammaKnife were unarchived from our clinical database. Treatment plans were generated for the two machines using the Prowess TPS (Prowess, Concord, CA). Plans were evaluated based on the beam-on time, conformity index (CI), isodose distribution, and dose-volume histograms.
Results: Comparable planes were achieved in most cases. The mean beam-on time for the studied cases was 25 minutes for CybeRay as compared to 17 minute for Galaxy. The mean CI was in the order of 1.9 for CybeRay as compared to 1.7 for Galaxy. Galaxy showed faster dose fall off in the axial view compared to CybeRay as can be seen by the spread of the lower isodose lines. On the other hand, the ring configuration of CybeRay allows treatment of extra-cranial body sites.
Conclusion: Both systems were capable of producing superior clinical treatment plans to meet our clinical acceptance criteria although Galaxy is specific for intracranial SRS/SRT while CybeRay is also capable of stereotactic body radiotherapy (SBRT).