Dosimetry of a novel rotating gamma system for stereotactic radiosurgery

This is the first report of the basic dosimetric properties of a new rotating gamma system: the RGS Vertex360^™. Dosimetric properties were compared to those measured with traditional rotating gamma systems and with the Leksell Gamma Knife. The RGS Vertex360 is similar to the original rotating gamma system developed by OUR New Medical Technology Development Co., Ltd. (Shenzen, China), however, there are a few notable differences including the angular arrangement of the sources. Basic dosimetric properties of the RGS Vertex360 were measured including: absorbed dose rate, output factors, mechanical and radiation center accuracy and dose profiles. A significant discrepancy was observed for the 4 mm output measured from the RGS Vertex360 compared to those obtained from previous rotating gamma units: the 4 mm output from the RGS Vertex360 (0.807) was 32-38% higher than those measured from previous units. This is somewhat surprising considering the excellent agreement in 4 mm outputs from the RGS Vertex360, the corresponding outputs specified by the manufacturer of the original OUR unit and those measured for the Leksell Gamma Knife. The mechanical accuracy was similar to previous rotating gamma systems while the 50-90% penumbra was narrower. Dose profiles compared favorably with the Leksell Gamma Knife: in many instances the measured penumbra was narrower for the RGS Vertex360. Notwithstanding the 4 mm output factor, the dosimetric properties of the RGS Vertex360 compared favorably with those of previous rotating gamma systems. The 4 mm output discrepancy was attributed to suboptimal alignment of the primary and secondary collimators in previous studies. The dosimetric properties of the RGS Vertex360 and the Leksell Gamma Knife were similar and, taken together, the results suggest that the new rotating gamma system is well suited for stereotactic radiosurgery procedures.