Department of Radiation Oncology, Cleveland Clinic, Cleveland, OH 44195, USA.
Med Phys. 2013 Feb;40(2):021722. doi: 10.1118/1.4789484.
To improve the accuracy of automatically segmented prostate, rectum, and bladder contours required for online adaptive therapy. The contouring accuracy on the current image guidance [image guided radiation therapy (IGRT)] scan is improved by combining contours from earlier IGRT scans via the simultaneous truth and performance level estimation (STAPLE) algorithm.
Six IGRT prostate patients treated with daily kilo-voltage (kV) cone-beam CT (CBCT) had their original plan CT and nine CBCTs contoured by the same physician. Three types of automated contours were produced for analysis. (1) Plan: By deformably registering the plan CT to each CBCT and then using the resulting deformation field to morph the plan contours to match the CBCT anatomy. (2) Previous: The contour set drawn by the physician on the previous day CBCT is similarly deformed to match the current CBCT anatomy. (3) STAPLE: The contours drawn by the physician, on each prior CBCT and the plan CT, are deformed to match the CBCT anatomy to produce multiple contour sets. These sets are combined using the STAPLE algorithm into one optimal set.
Compared to plan and previous, STAPLE improved the average Dice's coefficient (DC) with the original physician drawn CBCT contours to a DC as follows: Bladder: 0.81 ± 0.13, 0.91 ± 0.06, and 0.92 ± 0.06; Prostate: 0.75 ± 0.08, 0.82 ± 0.05, and 0.84 ± 0.05; and Rectum: 0.79 ± 0.06, 0.81 ± 0.06, and 0.85 ± 0.04, respectively. The STAPLE results are within intraobserver consistency, determined by the physician blindly recontouring a subset of CBCTs. Comparing plans recalculated using the physician and STAPLE contours showed an average disagreement less than 1% for prostate D98 and mean dose, and 5% and 3% for bladder and rectum mean dose, respectively. One scan takes an average of 19 s to contour. Using five scans plus STAPLE takes less than 110 s on a 288 core graphics processor unit.
Combining the plan and all prior days via the STAPLE algorithm to produce treatment day contours is superior to the current standard of deforming only the plan contours to the daily CBCT. STAPLE also improves the precision, with a substantial decrease in standard deviation, a key for adaptive therapy. Geometrically and dosimetrically accurate contours can be automatically generated with STAPLE on prostate region kV CBCT in a time scale suitable for online adaptive therapy.
提高在线自适应治疗所需的自动分割前列腺、直肠和膀胱轮廓的准确性。通过同时真实和性能水平估计（STAPLE）算法将早期 IGRT 扫描中的轮廓结合起来，从而提高当前图像引导[图像引导放射治疗（IGRT）]扫描中的轮廓准确性。
对 6 名接受每日千伏（kV）锥形束 CT（CBCT）治疗的 IGRT 前列腺患者进行了原始计划 CT 和 9 次 CBCT 轮廓勾画，由同一名医师进行。分析了三种类型的自动轮廓。（1）计划：通过将计划 CT 变形到每个 CBCT 上，然后使用产生的变形场将计划轮廓变形以匹配 CBCT 解剖结构。（2）前一天：通过将前一天的 CBCT 上的医生绘制的轮廓同样变形以匹配当前 CBCT 解剖结构。（3）STAPLE：将医生在每个先前的 CBCT 和计划 CT 上绘制的轮廓变形以匹配 CBCT 解剖结构，以生成多个轮廓集。使用 STAPLE 算法将这些集组合成一个最佳集。
与计划和前一天相比，STAPLE 提高了与原始医生绘制的 CBCT 轮廓的平均 Dice 系数（DC），具体如下：膀胱：0.81±0.13、0.91±0.06 和 0.92±0.06；前列腺：0.75±0.08、0.82±0.05 和 0.84±0.05；直肠：0.79±0.06、0.81±0.06 和 0.85±0.04。STAPLE 结果在盲法重新勾画一组 CBCT 的医生确定的观察者内一致性范围内。比较使用医生和 STAPLE 轮廓重新计算的计划显示，前列腺 D98 和平均剂量的平均差异小于 1%，膀胱和直肠平均剂量的差异分别小于 5%和 3%。勾画一个扫描平均需要 19 秒。在 288 核图形处理器单元上，使用五个扫描加 STAPLE 不到 110 秒。
通过 STAPLE 算法将计划和所有前几天的内容组合起来生成治疗日轮廓，优于仅将计划轮廓变形到每日 CBCT 的当前标准。STAPLE 还提高了精度，标准偏差大幅降低，这是自适应治疗的关键。在时间尺度上，STAPLE 可以在前列腺区域 kV CBCT 上自动生成具有良好几何形状和剂量准确性的轮廓，适用于在线自适应治疗。
