Schiffler Cancer Center, Wheeling, WV, USA.
J Appl Clin Med Phys. 2013 Mar 4;14(2):4141. doi: 10.1120/jacmp.v14i2.4141.
Implanted radiofrequency transponders were used for real-time monitoring of the intrafraction prostate displacement between patients in the prone position and the same patients in the supine position. Thirteen patients had three transponders implanted transperineally and were treated prone with a custom-fitted thermoplastic immobilization device. After collecting data from the last fraction, patients were realigned in the supine position and the displacements of the transponders were monitored for 5-7 minutes. Fourier transforms were applied to the data from each patient to determine periodicity and its amplitude. To remove auto correlation from the stream of displacement data, the distribution of short-term and long-term velocity components were calculated from Poincaré plots of paired sequential vector displacements. The mean absolute displacement was significantly greater prone than supine in the superior-inferior (SI) plane (1.2 ± 0.6 mm vs. 0.6 ± 0.4 mm, p= 0.015), but not for the lateral or anterior-posterior (AP) planes. Displacements were least in the lateral direction. Fourier analyses showed the amplitude of respiratory oscillations was much greater for the SI and AP planes in the prone versus the supine position. Analysis of Poincaré plots confirmed greater short-term variance in the prone position, but no difference in the long-term variance. The centroid of the implanted transponders was offset from the treatment isocenter by > 5 mm for 1.9% of the time versus 0.8% of the time for supine. These results confirmed significantly greater net intrafraction prostate displacement of patients in the prone position than in the supine position, but most of the difference was due to respiration-induced motion that was most pronounced in the SI and AP directions. Because the respiratory motion remained within the action threshold and also within our 5 mm treatment planning margins, there is no compelling reason to choose one treatment position over the other.
植入式射频应答器用于实时监测俯卧位和仰卧位患者的前列腺分次内位移。13 名患者经会阴植入 3 个应答器，并用定制的热塑固定装置俯卧位治疗。采集最后一个分次的数据后，患者在仰卧位重新定位，并监测应答器的位移 5-7 分钟。对每位患者的数据进行傅里叶变换，以确定周期性及其幅度。为了消除位移数据流中的自相关，从配对序贯向量位移的 Poincaré 图中计算短期和长期速度分量的分布。平均绝对位移在 SI 平面上俯卧位显著大于仰卧位（1.2±0.6mm 比 0.6±0.4mm，p=0.015），但在侧向或前后（AP）平面上则不然。侧向的位移最小。傅里叶分析显示，俯卧位时 SI 和 AP 平面的呼吸波动幅度明显大于仰卧位。Poincaré 图的分析证实，俯卧位时短期方差更大，但长期方差没有差异。植入应答器的质心在仰卧位时比俯卧位时偏移治疗等中心超过 5mm 的时间占 1.9%，而占 0.8%。这些结果证实，俯卧位患者的前列腺分次内位移明显大于仰卧位，但大部分差异是由于呼吸引起的运动所致，在 SI 和 AP 方向最为明显。由于呼吸运动仍在作用阈值内，也在我们 5mm 的治疗计划边缘内，因此没有令人信服的理由选择一种治疗体位而不是另一种。
