Department of Radiotherapy, Medical University Vienna/AKH Wien, Vienna, Austria.
Radiother Oncol. 2011 Feb;98(2):154-61. doi: 10.1016/j.radonc.2010.11.016. Epub 2010 Dec 20.
In-room cone-beam CT (CBCT) imaging and adaptive treatment strategies are promising methods to decrease target volumes and to spare organs at risk. The aim of this work was to analyze the inter-observer contouring uncertainties of target volumes and organs at risks (oars) in localized prostate cancer radiotherapy using CBCT images. Furthermore, CBCT contouring was benchmarked against other image modalities (CT, MR) and the influence of subjective image quality perception on inter-observer variability was assessed.
Eight prostate cancer patients were selected. Seven radiation oncologists contoured target volumes and oars on CT, MRI and CBCT. Volumes, coefficient of variation (COV), conformity index (cigen), and coordinates of center-of-mass (COM) were calculated for each patient and image modality. Reliability analysis was performed for the support of the reported findings. Subjective perception of image quality was assessed via a ten-scored visual analog scale (VAS).
The median volume for prostate was larger on CT compared to MRI and CBCT images. The inter-observer variation for prostate was larger on CBCT (CIgen=0.57±0.09, 0.61 reliability) compared to CT (CIgen=0.72±0.07, 0.83 reliability) and MRI (CIgen=0.66±0.12, 0.87 reliability). On all image modalities values of the intra-observer reliability coefficient (0.97 for CT, 0.99 for MR and 0.94 for CBCT) indicated high reproducibility of results. For all patients the root mean square (RMS) of the inter-observer standard deviation (σ) of the COM was largest on CBCT with σ(x)=0.4 mm, σ(y)=1.1 mm, and σ(z)=1.7 mm. The concordance in delineating OARs was much stronger than for target volumes, with average CIgen>0.70 for rectum and CIgen>0.80 for bladder. Positive correlations between CIgen and VAS score of the image quality were observed for the prostate, seminal vesicles and rectum.
Inter-observer variability for target volume delineation in prostate cancer is larger for CBCT-based contouring compared to CT and MRI. This factor of influence needs to be considered when defining safety margins for CBCT-based Adaptive Radiotherapy (ART).
在室锥形束 CT（CBCT）成像和自适应治疗策略是有前途的方法，可以减少目标体积并保护危险器官。本研究的目的是分析使用 CBCT 图像对局部前列腺癌放射治疗中目标体积和危险器官（OARs）的观察者间勾画不确定性。此外，还对 CBCT 勾画与其他成像方式（CT、MR）进行了基准测试，并评估了主观图像质量感知对观察者间变异性的影响。
选择了 8 例前列腺癌患者。7 名放射肿瘤学家在 CT、MRI 和 CBCT 上勾画了靶区和 OARs。为每位患者和每种图像方式计算了体积、变异系数（CV）、适形指数（cigen）和质量中心（COM）坐标。可靠性分析支持报告的结果。通过 10 分视觉模拟量表（VAS）评估了对图像质量的主观感知。
前列腺在 CT 上的体积中位数大于 MRI 和 CBCT 图像。前列腺的观察者间变异性在 CBCT 上更大（cigen=0.57±0.09，0.83 可靠性），而在 CT 上（cigen=0.72±0.07，0.83 可靠性）和 MRI 上（cigen=0.66±0.12，0.87 可靠性）。在所有图像方式上，观察者内可靠性系数的值（CT 为 0.97，MR 为 0.99，CBCT 为 0.94）均表明结果具有高度可重复性。对于所有患者，COM 的观察者间标准偏差（σ）的均方根（RMS）在 CBCT 上最大，分别为σ（x）=0.4mm、σ（y）=1.1mm 和 σ（z）=1.7mm。勾画 OARs 的一致性比目标体积要强得多，直肠的平均适形指数（cigen）>0.70，膀胱的平均适形指数（cigen）>0.80。观察到前列腺、精囊和直肠的适形指数（cigen）与图像质量的 VAS 评分之间存在正相关。
与 CT 和 MRI 相比，基于 CBCT 的勾画中前列腺癌靶区勾画的观察者间变异性更大。在定义基于 CBCT 的自适应放疗（ART）的安全边界时，需要考虑这一影响因素。
