摘要目的:为定量探讨基于历史CBCT的直肠癌患者全疗程膀胱充盈度变化。方法:回顾性选取2017年1月至2018年8月在北京大学肿瘤医院放疗的54例直肠癌患者的54组定位CT及213组治疗前实时锥形束CT（CBCT）图像，基于Eclipse计划系统分别勾画二维膀胱轮廓，并在三维重建后统计体积。利用SPSS软件分析放疗计划设计和实际执行时膀胱充盈度变化情况，以及性别、年龄和累积剂量等因素对膀胱充盈度的影响等。结果:54例患者放疗时的膀胱平均体积显著小于方案制定时的体积，差异达-155.85 cm 3。在入组患者中未观察到膀胱充盈度差异与性别、年龄存在明显相关性（ P>0.05）。随着治疗次数和累计剂量的增加，每次CBCT的膀胱充盈度与定位CT的膀胱充盈度差异均具有统计学意义（ P<0.05）。 结论:实际放疗时膀胱充盈度较方案设计时存在显著偏差，导致增加膀胱放射性损伤风险和临近肿瘤靶区剂量不确定性，临床可基于CBCT优化个体化膀胱充盈度定量分析和管理，以缩小精确放疗过程中的可控偏差。

abstractsObjective:To quantify the changes in bladder fullness throughout the course of radiotherapy in patients with rectal cancer based on historical CBCT data.Methods:Included in this retrospective study were 54 sets of localizing CT images and 213 sets of pre-treatment real-time cone beam CT (CBCT) images from 54 patients with rectal cancer undergoing radiotherapy in Peking University Cancer Hospital between January 2017 and August 2018. The images were subjected to two-dimensional outlining of the urinary bladder and calculation of the bladder volume after three-dimensional reconstruction, based on Eclipse planning system. SPSS software was used to analyze the difference in bladder fullness between the time of planning and during radiotherapy, as well as the influence of gender, age, and cumulative dose on the bladder fullness.Results:In the 54 patients, the mean bladder volume was significantly smaller during the radiotherapy than that at the time of planning, with a difference up to -155.85 cm 3. There was no significant correlation between the difference in bladder fullness and gender and age in the enrolled patients ( P>0.05) . With more sessions of radiotherapy and increasing cumulative dose, the difference in bladder fullness between CBCT and localizing CT became statistically significant ( P<0.05) . Conclusion:There is a significant difference in actual bladder fullness during radiotherapy compared with the time of planning. This leads to higher risk of radiation injury to the bladder and more dosimetric uncertainty adjacent to the tumor target area. In clinical settings, individualized quantitative analysis and management of bladder fullness can be optimized based on CBCT data to minimize the controllable deviation throughout precision radiotherapy.