Department of Radiology, Asan Medical Center, College of Medicine, University of Ulsan, Seoul, Republic of Korea.
Acta Oncol. 2011 May;50(4):539-46. doi: 10.3109/0284186X.2011.562916. Epub 2011 Mar 10.
To investigate inter-/intra-observer variability in defining the prostate by use of planning computed tomography (PCT) and cone beam CT (CBCT) with magnetic resonance image (MRI) as guidance prior to the introduction of an adaptive radiotherapy for prostate cancer.
We reviewed PCT and firstly acquired CBCT datasets of each ten patients with prostate cancer. Three physicians independently delineated the prostate based on PCT and CBCT with MRI as guidance, allowing determination of inter-physician variability. Two physicians repeated prostate contouring three times in total to investigate intra-physician variability. We compared delineated prostate volumes in terms of the generalized conformity index (CI(gen)), maximum variation ratio (MVR), and center of mass (COM).
There were no significant inter-/intra-observer differences in the estimation of prostate volume on both PCT and CBCT. For both inter- and intra-observer variability in contouring the prostate gland, there were no significant differences in MVR between PCT and CBCT. The CI(gen) for inter-observer variability was 0.74 by PCT and 0.69 by CBCT. The CI(gen) for intra-observer variability on PCT and CBCT was 0.84 and 0.81 for observer 2 and 0.76 and 0.73 for observer 3. COM analyses showed that the greatest inter-/intra-observer variability was in the measurement of the prostate apex and base. With respect to CI(gen) and COM analysis for the inter-observer variability, more precise delineation of the prostate was possible on PCT than CBCT. More precise contouring in terms of both CI(gen) and COM was demonstrated by observer 2 than observer 3.
Despite some ambiguity in apex and base level, there was a good consistency in delineating the gland on CBCT plus MRI-guided modification both among/within observer(s), without any significant difference from the consistency in defining the prostate on PCT. This study provides a framework for future studies of CBCT imaging of the prostate.
在引入前列腺癌自适应放疗之前，研究使用计划计算机断层扫描 (PCT) 和锥形束 CT (CBCT) 并结合磁共振成像 (MRI) 作为指导来定义前列腺时的观察者间和观察者内的可变性。
我们回顾性分析了十例前列腺癌患者的 PCT 和首次获取的 CBCT 数据集。三位医生分别根据 PCT 和 MRI 引导的 CBCT 进行前列腺勾画，以确定医生间的可变性。两位医生总共重复三次前列腺勾画，以研究医生内的可变性。我们比较了基于广义适形指数 (CI(gen))、最大变化比 (MVR) 和质心 (COM) 的勾画前列腺体积。
在 PCT 和 CBCT 上，对前列腺体积的估计没有明显的观察者间/内差异。对于勾画前列腺的观察者内和观察者间变异性，PCT 和 CBCT 之间的 MVR 没有显著差异。观察者间变异性的 CI(gen) 分别为 PCT 0.74 和 CBCT 0.69。观察者 2 和观察者 3 在 PCT 和 CBCT 上的观察者内变异性的 CI(gen) 分别为 0.84 和 0.81，0.76 和 0.73。COM 分析表明，在前列腺顶和底的测量中，观察者间和观察者内的变异性最大。就观察者间变异性的 CI(gen) 和 COM 分析而言，PCT 比 CBCT 更能精确地勾画前列腺。观察者 2 在 CI(gen) 和 COM 方面的勾画都比观察者 3 更精确。
尽管在前列腺顶和底的水平上存在一些模糊性，但在 CBCT 加 MRI 引导的修改后，在观察者间和观察者内勾画腺体的一致性较好，与在 PCT 上定义前列腺的一致性没有显著差异。本研究为今后的前列腺 CBCT 成像研究提供了框架。
