Yuan X, Strohbehn J W, Lynch D R, Johnsen M
Thayer School of Engineering, Dartmouth College, Hanover, NH 03755.
Int J Hyperthermia. 1990 Jan-Feb;6(1):227-40. doi: 10.3109/02656739009140818.
A four-applicator phased-array hyperthermia system with movable apertures (MA) is compared with an eight-applicator annular phased-array hyperthermia system with fixed apertures (AA) in terms of the HEP (hyperthermia equipment performance) values, based on two-dimensional models and the bioheat transfer equation. A hybrid element method is used to calculate the zeta-directed two-dimensional electric field with the inhomogeneities in tissue properties taken into account. The amplitudes and phases of each applicator are then optimized with the objective of uniform power deposition in the tumour and no power deposited in normal tissues. The temperature distributions under different blood flow conditions are obtained by solving the bioheat transfer equation using the finite element method. It is found that among the seven patient models studied, the MA and AA in general perform equally well when the tumour has zero blood flow, or equally poorly when the tumour has a blood flow larger than 5 ml/100 g per min. The performance of AA is often significantly better than that of MA when the tumour blood flow is 2.7 ml/100 g per min. The effects of different weighting functions are evaluated. We show that even if uniform absorbed power density (ARD = absorption rate density) could be achieved in the tumour volume with zero ARD in normal tissue the entire tumour would still not be brought to 43 degrees C or greater. However, it is found that the performance of uniform ARD in the tumour is on average far better than either the AA or MA, and choosing the uniform ARD as the objective function improved 35% of the cases for AA and 16% for MA. The optimization formula includes a weighting function that can be varied for different tissues. By decreasing the weights in regions of high blood flow the HEP values can sometimes be improved quite noticeably. Finally, the importance of the locations of applicators is studied. The results obtained indicate that the applicators should be placed about 5 cm or more away from the patient body (assuming water is the coupling medium) to ensure good HEP ratings.
基于二维模型和生物热传递方程，对具有可移动孔径（MA）的四阵元相控阵热疗系统与具有固定孔径（AA）的八阵元环形相控阵热疗系统的热疗设备性能（HEP）值进行了比较。采用混合元法计算考虑组织特性不均匀性的ζ方向二维电场。然后，以肿瘤内功率沉积均匀且正常组织无功率沉积为目标，对每个阵元的幅度和相位进行优化。利用有限元法求解生物热传递方程，得到不同血流条件下的温度分布。研究发现，在所研究的七个患者模型中，当肿瘤血流为零时，MA和AA的总体表现相当；当肿瘤血流大于5 ml/100 g per min时，二者表现同样较差。当肿瘤血流为2.7 ml/100 g per min时，AA的性能通常明显优于MA。评估了不同加权函数的影响。我们表明，即使在肿瘤体积内可实现均匀吸收功率密度（ARD = 吸收率密度）且正常组织ARD为零，整个肿瘤仍无法达到43摄氏度或更高温度。然而，发现肿瘤内均匀ARD的性能平均远优于AA或MA，选择均匀ARD作为目标函数可使AA的情况改善35%，MA的情况改善16%。优化公式包括一个可针对不同组织变化的加权函数。通过降低高血流区域的权重，有时HEP值可得到显著改善。最后，研究了阵元位置的重要性。所得结果表明，阵元应放置在距离患者身体约5 cm或更远的位置（假设水为耦合介质），以确保良好的HEP评级。
