Department of Radiation Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
Radiat Oncol. 2013 Jul 23;8:185. doi: 10.1186/1748-717X-8-185.
In-room cone-beam computerized tomography (CBCT) imaging is a promising method to reduce setup errors, especially in organs such as the bladder that often have large intrafractional variations due to organ movement. CBCT image quality is limited by low contrast and imaging artifacts, but few data have been reported about inter-observer variability of bladder boundary delineation on CBCT. The aim of this work was to analyze and evaluate the inter-observer contouring uncertainties of bladder boundary delineation on CBCT images in a prospective fashion.
Five radiation oncologists contoured 10 bladders using the CBCT datasets of consecutive 10 patients (including 4 females) who were irradiated to the pelvic region. Prostates were also contoured in male patients. Patients who had had prostatectomy were excluded. The coefficient of variation (COV), conformity index (CI(gen)), and coordinates of center-of-mass (COM) of the bladder and prostate were calculated for each patient.
The mean COV for the bladder and prostate was 0.08 and 0.20, respectively. The mean CI(gen) of the bladder and prostate was 0.81 and 0.66, respectively. The root mean square (RMS) of the inter-observer standard deviation (σ) of the COM displacement in the left-right (LR) and anterior-posterior (AP) direction was 0.79, 0.87 and 0.54 for the bladder and 0.63, 0.99 and 1.72 for the prostate. Regarding the mean COV and CI(gen) for the bladder, the differences between males and females were not significant.
Inter-observer variability for bladder delineation on CBCT images was substantially small regardless of gender. We believe that our results support the applicability of CBCT in adaptive radiotherapy for bladder cancer.
室内锥形束计算机断层扫描（CBCT）成像是一种有前途的方法，可以减少设置误差，特别是在膀胱等器官中，由于器官运动，这些器官通常存在较大的分次内变化。CBCT 图像质量受到低对比度和成像伪影的限制，但关于 CBCT 上膀胱边界勾画的观察者间可变性的数据很少。本研究旨在以前瞻性方式分析和评估 CBCT 图像上膀胱边界勾画的观察者间轮廓不确定性。
五位放射肿瘤学家使用连续 10 名（包括 4 名女性）接受盆腔照射的患者的 CBCT 数据集对 10 个膀胱进行轮廓勾画。在男性患者中还对前列腺进行了轮廓勾画。排除了接受前列腺切除术的患者。为每位患者计算了膀胱和前列腺的变异系数（COV）、一致性指数（CI(gen)）和质心（COM）坐标。
膀胱和前列腺的平均 COV 分别为 0.08 和 0.20。膀胱和前列腺的平均 CI(gen)分别为 0.81 和 0.66。膀胱和前列腺 COM 位移的观察者间标准差（σ）的均方根（RMS）在左右（LR）和前后（AP）方向分别为 0.79、0.87 和 0.54，0.63、0.99 和 1.72。关于膀胱的平均 COV 和 CI(gen)，男性和女性之间的差异没有统计学意义。
无论性别如何，CBCT 图像上膀胱勾画的观察者间可变性都很小。我们相信我们的结果支持 CBCT 在膀胱癌自适应放疗中的应用。
