Keqiang Wang1, Huipeng Meng2, Jie Chen3, Wenxue Zhang3, Yuanming Feng4. 1. Department of Biomedical Engineering, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, China; Department of Radiotherapy, Tianjin Medical University General Hospital, 154 Anshan Road, Heping District, Tianjin 300052, China. 2. Department of Biomedical Engineering, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, China. 3. Department of Radiotherapy, Tianjin Medical University General Hospital, 154 Anshan Road, Heping District, Tianjin 300052, China. 4. Department of Biomedical Engineering, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, China. Electronic address: ymfeng@tju.edu.cn.
Abstract
PURPOSE: To propose a "staggered overlap" technique in volumetric modulated arc therapy (VMAT) for craniospinal irradiation (CSI) and compare the dose distribution and plan robustness with "overlap" technique and "gradient optimization" approach. METHODS AND MATERIALS: 6 patients previously treated in our clinic were retrospectively selected. 9 VMAT plans of each patient were optimized with "staggered overlap", "overlap" and "gradient optimization" in overlapping region of 3 cm, 6 cm, and 9 cm separately. For the "staggered overlap" plan, adjacent field sets were intentionally overlapped by staggering field edges in an appropriate step size to avoid sharp dose gradient. Evaluation metrics including V95%, D2%, D98%, conformity number (CN) and homogeneity index (HI) were employed to evaluate the dose distribution. Moreover, shifts of the upper spinal field isocenter in each direction were performed to simulate junction errors for robustness analysis. RESULTS: The CN and HI of VMAT plans with "staggered overlap" were 0.82 (0.811-0.822) and 0.113 (0.112-0.114), while they were 0.778 (0.776-0.782) and 0.131 (0.130-0.131) for plans with "gradient optimization". In the robustness study, <3% dose deviations were found for 5 mm shifts in lateral and vertical directions with all techniques. In cranial-caudal direction, "overlap" technique created hot spots (D2% > 170%) and cold spots (D98% < 44%) in the junction region with 10 mm shifts. The dose deviations were decreased to 22% for plans with "staggered overlap" and 9 cm overlapping region. CONCLUSION: "Staggered overlap" technique provides better plan quality as compared to "gradient optimization" approach and makes the plan more robust against junction errors as compared to "overlap" technique.
PURPOSE: To propose a "staggered overlap" technique in volumetric modulated arc therapy (VMAT) for craniospinal irradiation (CSI) and compare the dose distribution and plan robustness with "overlap" technique and "gradient optimization" approach. METHODS AND MATERIALS: 6 patients previously treated in our clinic were retrospectively selected. 9 VMAT plans of each patient were optimized with "staggered overlap", "overlap" and "gradient optimization" in overlapping region of 3 cm, 6 cm, and 9 cm separately. For the "staggered overlap" plan, adjacent field sets were intentionally overlapped by staggering field edges in an appropriate step size to avoid sharp dose gradient. Evaluation metrics including V95%, D2%, D98%, conformity number (CN) and homogeneity index (HI) were employed to evaluate the dose distribution. Moreover, shifts of the upper spinal field isocenter in each direction were performed to simulate junction errors for robustness analysis. RESULTS: The CN and HI of VMAT plans with "staggered overlap" were 0.82 (0.811-0.822) and 0.113 (0.112-0.114), while they were 0.778 (0.776-0.782) and 0.131 (0.130-0.131) for plans with "gradient optimization". In the robustness study, <3% dose deviations were found for 5 mm shifts in lateral and vertical directions with all techniques. In cranial-caudal direction, "overlap" technique created hot spots (D2% > 170%) and cold spots (D98% < 44%) in the junction region with 10 mm shifts. The dose deviations were decreased to 22% for plans with "staggered overlap" and 9 cm overlapping region. CONCLUSION: "Staggered overlap" technique provides better plan quality as compared to "gradient optimization" approach and makes the plan more robust against junction errors as compared to "overlap" technique.
Authors: Sarah Barrett; Pierre Thirion; Dean Harper; Andrew J Simpkin; Michelle Leech; Kim Hickey; Laoise Ryan; Laure Marignol Journal: Rep Pract Oncol Radiother Date: 2019-09-04
Authors: Rami A El Shafie; Karina Böhm; Dorothea Weber; Kristin Lang; Fabian Schlaich; Sebastian Adeberg; Angela Paul; Matthias F Haefner; Sonja Katayama; Florian Sterzing; Juliane Hörner-Rieber; Sarah Löw; Klaus Herfarth; Jürgen Debus; Stefan Rieken; Denise Bernhardt Journal: Cancer Manag Res Date: 2019-01-17 Impact factor: 3.989