Visser A G, Deurloo I K, Levendag P C, Ruifrok A C, Cornet B, van Rhoon G C
Dr Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Int J Hyperthermia. 1989 Mar-Apr;5(2):265-76. doi: 10.3109/02656738909140452.
An interstitial hyperthermia system using thin, flexible wires operating at a frequency of 27 MHz has been evaluated for possible use in combination with (iridium) brachytherapy applications employing flexible nylon afterloading catheters. This method of interstitial heating is argued to be a variation of local-current-field heating, however with the direct galvanic contact between electrode and tissue replaced by a capacitive coupling between wire and tissue. Through a special design of the wire the length of the heated area along the catheter can be chosen freely. Standard non-prepared implantation catheters can be used, so that no change from the established implantation techniques is required. Possible advantages of these 27 MHz wires over coaxial dipole antennas at higher frequencies are simplicity and low cost of the heating system, free choice of effective heating length for each wire and uniformity of heating along this effective heating length up to the tip of the wire. Flexibility of the wires is maintained, enabling application in curved (even U-shaped) catheters, e.g. for head and neck implantations. Impedance matching of the wires to the generator, necessary for an optimal transfer of power, appears possible by means of a variable air coil. Care should be taken to avoid stray capacitances of the connecting cables with respect to ground or among the different cables used. Measurements in muscle-equivalent split phantoms with infrared thermography have been performed with both single and multiple wires. The resulting SAR distributions confirm the working principle of these low-frequency wires (resistive heating) and illustrate the difference with radiative antennas at higher frequencies. The system is being applied both in experimental animal studies and in a clinical pilot study.
一种使用细的柔性导线、工作频率为27兆赫的组织间热疗系统已被评估，看其是否有可能与采用柔性尼龙后装导管的（铱）近距离放射治疗应用相结合使用。这种组织间加热方法被认为是局部电流场加热的一种变体，不过电极与组织之间的直接电接触被导线与组织之间的电容耦合所取代。通过导线的特殊设计，可以自由选择沿导管的加热区域长度。可以使用标准的未预处理植入导管，因此无需改变既定的植入技术。与更高频率的同轴偶极天线相比，这些27兆赫导线可能具有的优点包括加热系统简单且成本低、每根导线的有效加热长度可自由选择以及沿此有效加热长度直至导线末端的加热均匀性。导线的柔韧性得以保持，能够应用于弯曲（甚至U形）导管，例如用于头颈部植入。通过可变空气线圈，似乎有可能使导线与发生器实现阻抗匹配，这对于功率的最佳传输是必要的。应注意避免连接电缆相对于地面或不同电缆之间的杂散电容。已使用单根和多根导线在肌肉等效分割体模中进行了红外热成像测量。所得的比吸收率分布证实了这些低频导线的工作原理（电阻加热），并说明了与更高频率的辐射天线的差异。该系统正在应用于实验动物研究和一项临床试点研究中。
