摘要目的:评估前列腺癌患者在线自适应放疗(OART)分次内临床靶区(CTV)的形变误差，为在线计划优化提供依据。方法:回顾性分析中国医学科学院肿瘤医院放疗科13例接受1.5 T磁共振引导OART的患者(8 Gy × 5次，共65个分次)，收集分次治疗开始和结束时的磁共振图像。由同一放疗医师勾画靶区和危及器官，采用刚性配准和三角面片化处理后，提取结构顶点。运用基于薄板样条的鲁棒点匹配算法(TPS-RPM)对CTV表面进行形变配准，获得点对应关系，最终计算分次内CTV的随机和系统形变误差。结果:分次内形变配准的平均豪斯多夫距离(HD)为(1.68±0.28)mm；分次内系统形变误差分别为(0.25 ± 3.18)mm (前后)、(0.89 ± 3.85)mm(左右)和(－1.98 ± 6.69)mm(上下)；分次内随机形变误差分别为(－0.26 ± 1.89)mm(前后)、(－0.08 ± 0.88)mm(左右)和(－0.04 ± 1.86)mm(上下)。结论:CTV在OART过程中主要发生上下方向的形变，应重点考虑上下方向的外扩边缘大小。

abstractsObjective:To assess intrafractional errors of the deformation of clinical target volumes (CTVs) during online adaptive radiotherapy (OART) for prostate cancer patients, aiming to provide a basis for online plan optimization.Methods:A retrospective analysis was conducted for 13 prostate cancer patients who received 1.5 T magnetic resonance imaging (MRI)-guided OART (8 Gy × 5 fractions, totaling 65 fractions) at the Department of Radiation Oncology, Cancer Hospital, Chinese Academy of Medical Sciences. The MRI images were collected at the beginning and end of various treatment fractions. Then, the CTVs and organs at risk (OARs) were delineated by the same radiation oncologist. After rigid registration and triangle mesh generation, the surface vertices were extracted. The deformable registration for the CTV surfaces was performed using the thin-plate spline robust point matching (TPS-RPM) algorithm, yielding vertex correspondences. Last, both systematic and random intrafractional errors of CTV deformation were calculated.Results:The average Hausdorff distance (HD) for deformable registration of treatment fractions was (1.68 ± 0.28) mm. The intrafractional systematic errors of CTV deformation were (0.25 ± 3.18) mm (anterior-posterior direction; A-P), (0.89 ± 3.85) mm (left-right direction, L-R), and (-1.98 ± 6.69) mm (superior-inferior direction, S-I). The intrafractional random errors of CTV deformation were determined at (-0.26 ± 1.89) mm (A-P), (-0.08 ± 0.88) mm (L-R), and (-0.04 ± 1.86) mm (S-I).Conclusions:During OART, CTV deformations primarily occur in the S-I direction. Therefore, it is necessary to consider the expanded size of margins in this direction during OART for prostate cancer.