Author: Minbin Chen, Gang Liu, Manju Liu, Weiwei Sang, Pulin Sun, Mingyuan Ye, Fang-Fang Yin, Lihua Zhang, Haiming Zhu 👨🔬
Affiliation: Jiahui International Hospital, Radiation Oncology, Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Medical Physics Graduate Program, Duke Kunshan University, Duke Kunshan University, The First People's Hospital of Kunshan 🌍
Purpose: This study aims to evaluate the effects of varying the number of arcs on treatment plans created using Volumetric Modulated Arc Therapy (VMAT) for Lattice radiotherapy (LRT).
Methods: Three patients with tumor volumes of 135cc, 1510cc and 1720cc, corresponding to tumors located in the lung, breast, and liver, respectively, were included in this study. Spherical high-dose lattice (PTV-66.7Gy) were delineated within the larger target volume (PTV-20Gy), with a diameter of 1cm and cm apart. Each case was replanned using VMAT with varying numbers of full arcs, using the Varian Eclipse 15.1 Treatment Planning System. Treatment was prescribed in four fractions. For the breast case, partial arcs were used with angles ranging from 181° to 100°. Treatment planning constraints were held constant across all plans with different number of arcs. Dose metrics assessed included the Conformity Index (CI), Homogeneity Index (HI), and dose values for D2%, D50%, D95%, D98%, as well as evaluation of typical organs-at-risk (OARs) using Dose-Volume Histogram (DVH).
Results: The CI values for all plans were above 0.9 for PTV-20. For PTV-66.7, the CI decreased sequentially across lung, liver, and breast cases. The HI for PTV-66.7 was lower in breast cases compared to others. The D95% values for PTV-20.0 and PTV-66.7 ranged from 16.7-18.7Gy and 59.1-70.2Gy, respectively, across all cases. The PVDR showed minimal variation across cases.
Conclusion: The study suggests that varying the number of arcs in VMAT lattice radiotherapy plans has minimal impact on dose coverage and parameters such as CI and HI within the same cases. However, since the number of arcs directly influences treatment time, using fewer arcs is preferable to achieve the same dosage effect.