Ryan T P, Backus V L, Coughlin C T
Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA.
Int J Hyperthermia. 1995 Mar-Apr;11(2):187-209. doi: 10.3109/02656739509022456.
Superficial hyperthermia with present day applicators provides a challenge when tumours exceed several cm in diameter. Unless microstrip applicators are scanned, the usable heat region often falls short of treating the entire region with 50% power or specific absorption rate (SAR). New microstrip applicator designs were evaluated through SAR analysis and compared to the traditional microstrip applicators used in the clinic at Dartmouth over the past six years. The new designs included fabricating thin archimedean spirals (1.0 mm strip width) incorporating dielectric substrate (epsilon = 5.3-10.8). The designs were optimized at 433 MHz for an arm length of 59 cm. Measurements in a plane 1.0 cm from the surface showed that thin spirals outperformed traditional designs by increasing the 50% SAR area by a factor of 2.5, while maintaining the same physical size. Arrays of four elements were fabricated from thin spirals, although SAR evaluation showed only 10-20% SAR between elements. Since this was deemed unacceptable and the design goal was to fabricate a stationary applicator that had at least 50% SAR between elements, dual element designs were created with gradually overlapped elements. It was found that overlapping three coils of the spiral created a large region that equalled or exceeded 50% SAR that could not be matched by single applicators. Coherent operation of the dual spiral array resulted in more central power deposition and incoherent operation resulted in more peripheral power deposition. SAR measurements at the fat/muscle interface showed an elongated heating pattern in hydroxyethylcellulose muscle equivalent phantom. Power deposition 1.0 cm deep in muscle retained the same basic size and shape with or without the fat layer. Patient treatments for chestwall tumours confirmed that the dual overlapping applicator heated a larger region without the sharp temperature peak associated with single applicators.
当肿瘤直径超过几厘米时，使用当今的施热器进行浅表热疗会面临挑战。除非对微带施热器进行扫描，否则可用的加热区域通常无法以50%的功率或比吸收率（SAR）治疗整个区域。通过SAR分析对新的微带施热器设计进行了评估，并与过去六年在达特茅斯诊所使用的传统微带施热器进行了比较。新设计包括制造结合介电基板（ε = 5.3 - 10.8）的薄阿基米德螺旋（条带宽度为1.0毫米）。这些设计在433 MHz下针对59厘米的臂长进行了优化。在距表面1.0厘米的平面上进行的测量表明，薄螺旋通过将50% SAR区域增加2.5倍，在保持相同物理尺寸的情况下，性能优于传统设计。由薄螺旋制成了四个元件的阵列，尽管SAR评估显示元件之间的SAR仅为10 - 20%。由于这被认为是不可接受的，并且设计目标是制造一种在元件之间至少有50% SAR的固定施热器，因此创建了具有逐渐重叠元件的双元件设计。发现重叠螺旋的三个线圈会产生一个等于或超过50% SAR的大区域，这是单个施热器无法比拟的。双螺旋阵列的相干操作导致更多的中心功率沉积，而非相干操作导致更多的外围功率沉积。在脂肪/肌肉界面处的SAR测量显示，在羟乙基纤维素肌肉等效体模中存在拉长的加热模式。在有或没有脂肪层的情况下，肌肉中1.0厘米深处的功率沉积保持相同的基本尺寸和形状。对胸壁肿瘤的患者治疗证实，双重叠施热器加热的区域更大，且没有与单个施热器相关的尖锐温度峰值。
