C. Zheng1, Y. Zhang2, Z. Dai3, Y. Liu4, H. Li4, and L. Hu4; 1Cancer Hospaital Chinese Academy of Medical Sciences,Shenzhen Center, Shenzhen, Guangdong, China, 2Cancer Hosptial Chinese Academy of Medical Sciences,Shenzhen Center, ShenZhen, GuangDong, China, 3National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, ShenZhen, Guangdong, China, 4Cancer Hosptial Chinese Academy of Medical Sciences,Shenzhen Center, Shenzhen, Guangdong, China
Purpose/Objective(s): The aim of this study is to investigate the influence of different immobilization techniques on the margin expansion of the Planning Target Volume (PTV) during the frameless robotic radiosurgery system radiotherapy for intracranial tumors. Materials/
Methods: Sixty-three cases of patients with intracranial tumors treated using the CK-M6 were selected.The patients were categorized into two groups based on distinct immobilization techniques. One is the thermoplastic pad group, which consisted of 40 patients immobilized using a head-neck-shoulder frame, B-pillow, and thermoplastic cushion, in addition to a thermoplastic film. Another is the foam group, which comprised 23 patients immobilized with a head-neck-shoulder frame, foam, and thermoplastic film. The conclusion was reached through the calculation of the influence of positional errors during treatment on the size of the PTV expansion boundary, employing the van Herk margin formula. Results: This study uncovered errors during the treatment process. Our analysis of average error results indicated that the calculation of expansion in the X-axis, Y-axis, and Z-axis directions should be incorporated into the clinical determination of PTV expansion boundaries.Our findings showed that in the thermoplastic pad group, the expansion measurements were 1.00mm along the X-axis, 1.00mm along the Y-axis, and 0.8mm along the Z-axis. In contrast, for the foam group, the expansion was 1.10mm along the X-axis, 1.17mm along the Y-axis, and 1.23mm along the Z-axis. Conclusion: In comparing the two fixation methods, the thermoplastic pad group exhibited a smaller expansion boundary compared to the foam group.Consequently, the recommended fixation method for CK radiotherapy of intracranial tumors involves the use of a head-neck-shoulder frame, B-pillow, thermoplastic cushion, and head-neck-shoulder thermoplastic film fixation. Keywords: CyberKnife; Fixed Techniques; Intracranial Tumors; 6D-skull Tracking; PTV margin
