Van Rhoon G C, Van Der Heuvel D J, Ameziane A, Rietveld P J M, Volenec K, Van Der Zee J
Erasmus MC-Daniel den Hoed Cancer Center, Department of Radiation Oncology, Unit Hyperthermia, PO Box 5201, 3008 AE, Rotterdam, The Netherlands.
Int J Hyperthermia. 2003 Nov-Dec;19(6):642-54. doi: 10.1080/0265673031000140813.
Characterization of the performance of an hyperthermia applicator by phantom experiments is an essential aspect of quality assurance in hyperthermia. The objective of this study was to quantitatively characterize the energy distribution of the Sigma-60 applicator of the BSD2000 phased array system operated within the normal frequency range of 70-120 MHz. Additionally, the accuracy of the flexible Schottky diode sheet to measure E-field distributions was assessed.
The flexible Schottky diode sheet (SDS) consists of 64 diodes mounted on a flexible 125 microm thick polyester foil. The diodes are connected through high resistive wires to the electronic readout system. With the SDS E-field distributions were measured with a resolution of 2.5 x 2.5 cm in a cylindrical phantom, diameter of 26 cm and filled with saline water (2 g/l). The phantom was positioned symmetrically in the Sigma-60 applicator. RF-power was applied to the 4-channel applicator with increasing steps from 25W to a total output of 400 W.
The complete system to measure the E-field distribution worked fine and reliably within the Sigma-60 applicator. The E-field distributions measured showed that the longitudinal length of the E-field distribution is more or less constant, e.g. 21-19 cm, over the frequency range of 70-120 MHz, respectively. As expected, the radial E-field distributions show a better focusing towards the centre of the phantom for higher frequencies, e.g. from 15.3-8.7 cm diameter for 70-120 MHz, respectively. The focusing target could be moved accurately from the left to the right side of the phantom. Further it was found that the sensitivity variation of nine diodes located at the centre of the phantom was very small, e.g. < 3% over the whole frequency range.
The SAR distributions of the Sigma-60 applicator are in good agreement with theoretically expected values. The flexible Schottky diode sheet proves to be an excellent tool to make accurate, quantitative measurements of E-field distributions at low (25 W) and medium (400 W) power levels. An important feature of the SDS is that it enables one to significantly improve quantitative quality assurance procedures and to start quantitative comparisons of the performance of the different deep hyperthermia systems used by the various hyperthermia groups.
通过体模实验表征热疗设备的性能是热疗质量保证的一个重要方面。本研究的目的是定量表征在70 - 120 MHz正常频率范围内运行的BSD2000相控阵系统的Sigma - 60设备的能量分布。此外，还评估了柔性肖特基二极管片测量电场分布的准确性。
柔性肖特基二极管片（SDS）由安装在125微米厚的柔性聚酯箔上的64个二极管组成。二极管通过高阻线连接到电子读出系统。使用SDS在直径26厘米、充满盐水（2克/升）的圆柱形体模中以2.5×2.5厘米的分辨率测量电场分布。体模对称放置在Sigma - 60设备中。向4通道设备施加射频功率，功率从25瓦逐步增加到总输出400瓦。
用于测量电场分布的整个系统在Sigma - 60设备内运行良好且可靠。测量的电场分布表明，在70 - 120 MHz频率范围内，电场分布的纵向长度大致恒定，例如分别为21 - 19厘米。正如预期的那样，对于更高频率，径向电场分布向体模中心的聚焦更好，例如对于70 - 120 MHz，直径分别从15.3 - 8.7厘米。聚焦目标可以准确地从体模的左侧移动到右侧。此外还发现，位于体模中心的九个二极管的灵敏度变化非常小，例如在整个频率范围内<3%。
Sigma - 60设备的比吸收率（SAR）分布与理论预期值高度吻合。柔性肖特基二极管片被证明是在低（25瓦）和中（400瓦）功率水平下对电场分布进行准确、定量测量的优秀工具。SDS的一个重要特点是它能够显著改进定量质量保证程序，并开始对不同热疗组使用的不同深部热疗系统的性能进行定量比较。
