Diederich C J, Khalil I S, Stauffer P R, Sneed P K, Phillips T L
University of California, San Francisco-Radiation Oncology Department, San Francisco, CA 94143-0226, USA.
Int J Hyperthermia. 1996 May-Jun;12(3):401-19. doi: 10.3109/02656739609022527.
This study presents the design and performance evaluation of interstitial ultrasound applicators designed specifically for thermal therapy with simultaneous brachytherapy. The applicator consists of a multielement array of piezoceramic tubular radiators, each with separate power control, surrounded by thin layers of electrically-insulating and biocompatible coatings (< 2.6 mm OD). A catheter which is compatible with remote afterloaders and standard brachytherapy technology forms the inner lumen. These 'direct-coupled interstitial ultrasound applicators' (DCIUA's) are placed within the tumour or target region, with the coated transducer surface forming the outer wall of the implant catheter. Thermocouple sensors embedded in the coating over each transducer can be used for continuous monitoring of the tissue/applicator interface temperatures for feedback control of power to each transducer segment. Theoretical acoustic power deposition and corresponding temperature distributions from thermal simulations have demonstrated that the radius of effective heating is highly dependent upon the acoustic efficiency of the piezoceramic transducers, with effective heating extending > 1 - 1.5 cm radially for typical DCIUA applicators that are 60-65% efficient. This exceeds the effective heating radius of both thermal conduction and RF heating technologies. Measurements with prototype multielement ultrasound applicators have demonstrated acoustic efficiencies between 60 and 65% and beam distributions which are fairly uniform and collimated to the transducer axial length. Thermal dosimetry measurements within in vivo tissues have demonstrated controllable therapeutic temperature rises at 1 - 1.5 cm radial depth from the applicators, which were in agreement with the simulations. This study demonstrates that direct-coupled ultrasound applicators, designed without an active cooling mechanism in order to accommodate the insertion of radiation sources, are practicable for simultaneous thermobrachytherapy and promises to give more adjustable heating patterns than current alternative techniques.
本研究介绍了专门为热疗与同步近距离放射治疗设计的组织间超声 applicators 的设计与性能评估。该 applicator 由压电陶瓷管状辐射器的多元素阵列组成，每个辐射器都有独立的功率控制，周围包裹着电绝缘且生物相容的薄层涂层（外径<2.6 毫米）。与远程后装治疗机和标准近距离放射治疗技术兼容的导管形成内腔。这些“直接耦合组织间超声 applicators”（DCIUA）放置在肿瘤或靶区内，带涂层的换能器表面形成植入导管的外壁。嵌入每个换能器涂层中的热电偶传感器可用于连续监测组织/ applicator 界面温度，以反馈控制每个换能器段的功率。热模拟得出的理论声功率沉积和相应温度分布表明，有效加热半径高度依赖于压电陶瓷换能器的声效率，对于效率为 60 - 65%的典型 DCIUA applicators，有效加热在径向延伸>1 - 1.5 厘米。这超过了热传导和射频加热技术的有效加热半径。使用原型多元素超声 applicators 的测量表明，声效率在 60%至 65%之间，且波束分布相当均匀，并沿换能器轴向长度准直。体内组织内的热剂量测量表明，在距 applicators 径向深度 1 - 1.5 厘米处可实现可控的治疗温度升高，这与模拟结果一致。本研究表明，为适应放射源插入而设计且无主动冷却机制的直接耦合超声 applicators 对于同步热近距离放射治疗是可行的，并且有望提供比当前替代技术更可调节的加热模式。
