Institute of Clinical Research, University of Southern Denmark, Odense, Denmark
Acta Oncol. 2013 Aug;52(6):1168-74. doi: 10.3109/0284186X.2012.747698. Epub 2012 Dec 17.
The intra-fractional movement of the prostate constitutes a hindrance for the reduction of the planning target volume margin for prostate cancer patients. Monitoring the movement of the prostate during treatment is a promising but in most centres not feasible solution. However, the projection images of the pre-treatment cone-beam computed tomography (CBCT) provide information about the motion of the target immediately preceding the treatment. This motion information can be extracted from any standard CBCT scan which is available in many institutions. In this study we measure the motion of the prostate during the pre-treatment CBCT and investigate whether this motion is correlated with the intra-fractional movement of the prostate.
Pre- and post-treatment CBCT scans were made during a number of the fractions (average 11 range 8-12) for 13 prostate cancer patients during the radiation treatment course. The displacement of the post-treatment CBCT scans relative to the pre-treatment position was used to assess the intra-fractional motion. Automated image analysis was used to track the 2D position of radiopaque markers in the projection images of the scans. The most probable 3D trajectory of the markers during the CBCT scan was estimated based on a probability density function which was established for each individual scan.
The accuracy of the tracking algorithm was found satisfactory and the motion of the markers during the CBCT scans was successfully extracted from the projection images. This motion was generally small and uncorrelated with the subsequent intra-fractional movement of the prostate. The correlation coefficients were 20.05, 0.07, and 20.05 in the LR, AP, and CC direction, respectively.
It is tempting to exploit the pre-treatment CBCT to predict the intra-fractional movement of the prostate but, unfortunately, we have found no correlation between the intra-fractional movement and the motion of the prostate immediately prior to treatment.
前列腺的分次内运动是降低前列腺癌患者计划靶区边缘的障碍。在治疗过程中监测前列腺的运动是一种有前途但在大多数中心不可行的解决方案。然而，治疗前锥形束计算机断层扫描（CBCT）的投影图像提供了治疗前即刻靶区运动的信息。这种运动信息可以从许多机构提供的任何标准 CBCT 扫描中提取。在这项研究中，我们测量了治疗前 CBCT 期间前列腺的运动，并研究了这种运动是否与前列腺的分次内运动相关。
在放射治疗过程中，对 13 例前列腺癌患者的多个分次（平均 11 次，范围 8-12 次）进行了治疗前和治疗后 CBCT 扫描。使用治疗后 CBCT 扫描相对于治疗前位置的位移来评估分次内运动。使用自动图像分析来跟踪扫描投影图像中不透射线标记物的 2D 位置。根据为每个单独扫描建立的概率密度函数，估计标记物在 CBCT 扫描期间的最可能 3D 轨迹。
跟踪算法的准确性令人满意，并且成功地从投影图像中提取了 CBCT 扫描期间标记物的运动。这种运动通常很小，与随后的前列腺分次内运动无关。在 LR、AP 和 CC 方向上的相关系数分别为 20.05、0.07 和 20.05。
利用治疗前的 CBCT 来预测前列腺的分次内运动是很有吸引力的，但不幸的是，我们没有发现分次内运动与治疗前前列腺的运动之间存在相关性。
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