Wust P, Berger J, Fähling H, Nadobny J, Gellermann J, Tilly W, Rau B, Petermann K, Felix R
Department of Radiation Oncology, Charité Medical School, Berlin, Germany.
Int J Radiat Oncol Biol Phys. 1999 Mar 1;43(4):927-37. doi: 10.1016/s0360-3016(98)00490-8.
A measurement device for noninvasive and simultaneous control of antennas during regional radiofrequency (rf) hyperthermia and, subsequently, the estimation of the power distribution in the interior of patients are essential preconditions for further technological progress. Aiming at this, the feasibility of an electro-optical electric field sensor was investigated during clinical rf hyperthermia.
The electro-optical electric field (E-field) sensor is based on lithiumniobate crystals and the Mach-Zehnder interferometer structure, and was tested in an earlier phantom study. For this study, a mechanical scanning device was developed allowing the registration of the E-field during clinical application. Data were recorded along a curve in the water bolus of the SIGMA 60 applicator of the annular phased-array system BSD-2000 (BSD Medical Corp., Salt Lake City, UT) close to the base points of the flat biconical dipole antennas. The results were compared with modeling calculations using the finite-difference time-domain (FDTD) method. For the latter, different antenna models were assumed. For systematic registration of the E-field curves in amplitude and phase, we employed an elliptical lamp phantom with fat-equivalent ring (filled with saline solution) and an elliptical polyacrylamide phantom with acrylic glass wall. Further measurements were carried out during the treatment of 5 patients with 20 hyperthermia treatments.
Data of both phantom and patient measurements can be satisfactorily described by the FDTD method, if the antenna model is refined by taking into account the conical form of the dipoles and the special dielectric environment of the feeding point. Phase deviations can be entered ex posteriori for correction in the calculation algorithm. A comparison of amplifier power measurement (forward and backward power) and bolus E-field scans near the antenna base points demonstrates that E-field measurements between antennas and patient are a necessity for the appropriate characterization of antenna radiation properties. These measurements are sensitive to variations of the lossy medium in position and shape, and can be correctly predicted with current models. However, the differences between different patients are moderate and unspecific in both calculations and measurements, with fluctuations at maximum of 30 degrees in phases and 40% in amplitudes.
The measurement method presented here turned out to be a practical tool for online registration of E-fields in phases and amplitudes along arbitrary curves in a water bolus or phantom. It can be utilized to evaluate antenna design and modeling calculations and leads, thus, to a better understanding of complicated multiantenna systems. In clinical routine, it can be employed as input for patient-specific hyperthermia planning and, finally, for the realization of online control with subsequent optimization of the power distribution in the patient.
在局部射频（rf）热疗过程中对天线进行无创且同步控制的测量装置，以及随后对患者体内功率分布的估计，是进一步技术进步的基本前提条件。针对此，研究了临床rf热疗过程中电光电场传感器的可行性。
电光电场（E场）传感器基于铌酸锂晶体和马赫曾德尔干涉仪结构，且已在早期的体模研究中进行了测试。对于本研究，开发了一种机械扫描装置，可在临床应用期间记录E场。数据沿着环形相控阵系统BSD - 2000（BSD Medical Corp.，盐湖城，犹他州）的SIGMA 60施源器水囊内靠近扁平双锥形偶极天线基点的一条曲线进行记录。将结果与使用时域有限差分（FDTD）方法的建模计算进行比较。对于后者，假设了不同的天线模型。为了系统记录E场曲线的幅度和相位，我们采用了带有脂肪等效环（填充有盐溶液）的椭圆形灯体模和带有丙烯酸玻璃壁的椭圆形聚丙烯酰胺体模。在对5名患者进行20次热疗治疗期间进行了进一步测量。
如果通过考虑偶极子的锥形形式和馈电点的特殊介电环境来完善天线模型，FDTD方法可以令人满意地描述体模和患者测量的数据。相位偏差可以事后输入到计算算法中进行校正。天线基点附近放大器功率测量（正向和反向功率）与水囊E场扫描的比较表明，天线与患者之间的E场测量对于适当表征天线辐射特性是必要的。这些测量对有损介质在位置和形状上的变化敏感，并且可以用当前模型正确预测。然而，不同患者之间的差异在计算和测量中都是中等且非特异性的，相位最大波动为30度，幅度最大波动为40%。
本文提出的测量方法被证明是一种实用工具，可用于在线记录水囊或体模中沿任意曲线的E场的相位和幅度。它可用于评估天线设计和建模计算，从而更好地理解复杂的多天线系统。在临床常规中，它可作为患者特异性热疗计划的输入，最终用于实现在线控制以及随后优化患者体内的功率分布。
