Author: Jian Chen, Qiufen Guo, Aihua Li, Jing Liu, Junjie MA, Qian WU, Haonan Xiao, Peng Xie, Xiaohui Yan, Yong Yin, Zhe Zhang 👨🔬
Affiliation: Department of Radiation Oncology, Peking University Shenzhen Hospital, Department of Radiation Oncology and Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Department of Obstetrics and Gynaecology, Liao Cheng People’s Hospital 🌍
Purpose: Online Adaptive radiation therapy (ART) has been an effective technique to manage patient’s inter-fractional anatomical changes and therefore reduces planning target volume (PTV). However, online ART requires long on-couch time for plan re-optimization and intra-fractional motions may increase. This study aims to develop and validate a personalized anisotropic margin strategy to address intra-fractional motion in cervical cancer online ART that minimizes the PTVs while maintaining the coverage to clinical target volumes (CTVs).
Methods: This study included 196 online ART sessions of 7 patients, and each session included two iterative cone-beam computed tomography (iCBCT) scans: one after positioning and another prior to beam delivery. The observed CTV intra-fractional motions in the first 5 fractions of each patient determined the personalized anisotropic margins, which were iteratively reduced in each direction (anterior, posterior, left, right, superior, and inferior) in an automatic program to minimize the resulting PTV while maintaining 99% CTV coverage. The proposed margins were compared with conventional 5 mm isotropic margins, both geometrically and dosimetrically. In the geometrical comparison, PTV volumes, CTV coverages, and doses to organs at risk (OARs) in the reference plans were assessed. In the dosimetric comparison, the sixth to the tenth fractions of each patient were re-treated on emulators, and the doses deposited in the pseudo-CT (sCT) were compared.
Results: The personalized anisotropic margins reduced PTV volumes by 16% (p<0.001), and the doses to critical OARs, including small intestines, bladders, and rectums, were significantly decreased. CTV coverage was maintained at 99.05 ± 0.29 % in the geometric evaluation and 98.45 ± 0.88 % in the dosimetric evaluation.
Conclusion: The proposed personalized anisotropic margin strategy significantly reduced the damage to healthy tissues while maintaining adequate CTV coverage, which may facilitate the clinical implementation of online ART and maximize the benefits for cervical cancer patients.