Department of Oncology, University Hospital Ostrava, 17. listopadu 1790, 708 52, Ostrava, Czech Republic.
Radiat Oncol. 2021 Dec 7;16(1):235. doi: 10.1186/s13014-021-01958-4.
To report prostate deformation during treatment, based on an analysis of fiducial marker positional differences in a large sample.
This study included 144 patients treated with prostate stereotactic body radiation therapy after implantation in each of 4 gold fiducial markers (FMs), which were located and numbered consistently. The center of mass of the FMs was recorded for every pair of X-ray images taken during treatment. The distance between each pair of fiducials in the live X-ray images is calculated and compared with the respective distances as determined in the CT volume. The RBE is the difference between these distances. Mean RBE and intrafraction and interfraction RBE were evaluated. The intrafraction and intefraction RBE variability were defined as the standard deviation, respectively, of all RBE during 1 treatment fraction and of the mean daily RBE over the whole treatment course.
We analyzed 720 treatment fractions comprising 24,453 orthogonal X-ray image acquisitions. We observed a trend to higher RBE related to FM4 (apex) during treatment. The fiducial marker in the prostate apex could not be used in 16% of observations, in which RBE was > 2.5 mm. The mean RBEavg was 0.93 ± 0.39 mm (range 0.32-1.79 mm) over the 5 fractions. The RBEavg was significantly lower for the first and second fraction compared with the others (P < .001). The interfraction variability of RBEavg was 0.26 ± 0.16 mm (range 0.04-0.74 mm). The mean intrafraction variability of all FMs was 0.45 ± 0.25 mm. The highest Pearson correlation coefficient was observed between FM2 and FM3 (middle left and right prostate) (R = 0.78; P < .001). Every combination with FM4 yielded lower coefficients (range 0.66-0.71; P < .001), indicating different deformation of the prostate apex.
Ideally, prostate deformation is generally small, but it is very sensitive to rectal and bladder filling. We observed RBE up to 11.3 mm. The overall correlation between FMs was affected by shifts of individual fiducials, indicating that the prostate is not a "rigid" organ. Systematic change of RBE average between subsequent fractions indicates a systematic change in prostate shape.
基于大样本中基准标记位置差异的分析，报告治疗过程中的前列腺变形。
本研究包括 144 名接受前列腺立体定向体放射治疗的患者，在 4 个金基准标记物（FM）中每个标记物植入后进行治疗，这些标记物的位置和编号始终保持一致。在治疗过程中拍摄的每对 X 射线图像中记录质量中心。计算活 X 射线图像中每对基准之间的距离，并将其与 CT 容积中确定的相应距离进行比较。RBE 是这些距离之间的差异。评估平均 RBE 以及分次内和分次间 RBE。将各治疗分数内的所有 RBE 的标准差分别定义为分次内 RBE 变异性，将整个治疗过程中每日平均 RBE 的标准差定义为分次间 RBE 变异性。
我们分析了 720 个治疗分数，共包含 24453 个正交 X 射线图像采集。我们观察到在治疗过程中与 FM4（顶点）相关的 RBE 呈上升趋势。在 16%的观察中，前列腺顶点的基准标记物无法使用，RBE>2.5mm。在 5 个分数中，RBEavg 的平均值为 0.93±0.39mm（范围 0.32-1.79mm）。与其他分数相比，第一和第二分数的 RBEavg 明显较低（P<.001）。RBEavg 的分次间变异性为 0.26±0.16mm（范围 0.04-0.74mm）。所有 FM 的平均分次内变异性为 0.45±0.25mm。FM2 和 FM3（左中右前列腺）之间观察到的最高 Pearson 相关系数为 0.78（P<.001）。与 FM4 的每个组合的相关系数均较低（范围 0.66-0.71；P<.001），表明前列腺顶点的变形不同。
理想情况下，前列腺变形通常很小，但对直肠和膀胱充盈非常敏感。我们观察到的 RBE 高达 11.3mm。FM 之间的整体相关性受到个别基准点移位的影响，表明前列腺不是“刚性”器官。后续分数之间 RBE 平均值的系统性变化表明前列腺形状的系统性变化。
