Comparison of Intrafractional Motion in Head and Neck Cancer Between Two Immobilization Methods During Stereotactic Ablative Radiation Therapy by CyberKnife

Abstract

Chen-Lin Kang,1– 3 Tsair-Fwu Lee,1,4,5 Shan-Ho Chan,2 Shyh-Chang Liu,3 Jui-Chu Wang,6 Cheng-Hsiang Tsai,1 Kuan-Cho Liao,1 Fu-Min Fang,1 Liyun Chang,7 Chun-Chieh Huang1,8 1Department of Radiation Oncology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan; 2Department of Medical Imaging and Radiology, Shu-Zen Junior College of Medicine and Management, Kaohsiung, Taiwan; 3Department of Information Engineering, I-Shou University, Kaohsiung, Taiwan; 4Medical Physics and Informatics Laboratory of Electronics Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan; 5Biomedical Engineering, Kaohsiung Medical University, Kaohsiung, Taiwan; 6Department of Anatomical Pathology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan; 7Department of Medical Imaging and Radiological Sciences, I-Shou University, Kaohsiung, Taiwan; 8Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan, TaiwanCorrespondence: Chun-Chieh HuangDepartment of Radiation Oncology, Kaohsiung Chang Gung Memorial Hospital, No 123, Dapi Road, Niaosong Dist., Kaohsiung 833, TaiwanTel [phone]Fax [phone]Email [email protected]: Maintaining immobilization to minimize spine motion is very important during salvage stereotactic ablative radiation therapy (SABR) for recurrent head and neck cancer. This study aimed to compare the intrafractional motion between two immobilization methods.Patients and Methods: With a spine tracking system for image guiding, 9094 records from 41 patients receiving SABR by CyberKnife were obtained for retrospective comparison. Twenty-one patients were immobilized with a thermoplastic mask and headrest (Group A), and another 20 patients used a thermoplastic mask and headrest together with a vacuum bag to support the head and neck area (Group B). The intrafractional motion in the X (superior-inferior), Y (right-left), Z (anterior-posterior) axes, 3D (three-dimensional) vector, Roll, Pitch and Yaw in the two groups was compared. The margins of the planning target volume (PTV) to cover 95% intrafractional motion were evaluated.Results: The translational movements in the X-axis, Y-axis, and 3D vector in Group A were significantly smaller than in Group B. The rotational errors in the Roll and Yaw in Group A were also significantly smaller than those in Group B; conversely, those in the Pitch in Group A were larger. To cover 95% intrafractional motion, margins of 0.96, 1.55, and 1.51 mm in the X, Y and Z axes, respectively were needed in Group A, and 1.06, 2.86, and 1.34 mm, respectively were required in Group B.Conclusion: The immobilization method of thermoplastic mask and head rest with vacuum bag did not provide better immobilization than that without vacuum bag in most axes. The clinical use of 2 mm as a margin of PTV to cover 95% intrafractional motion was adequate in Group A but not in Group B.Keywords: stereotactic ablative radiation therapy, CyberKnife, intrafractional motion, immobilization method, head and neck cancer

Keywords

• stereotactic ablative radiation therapy
• cyberknife
• intrafractional motion
• immobilization method
• head and neck cancer