Chou C K, McDougall J A, Chan K W, Luk K H
Department of Radiation Research, City of Hope National Medical Center, Duarte, CA 91010.
Int J Radiat Oncol Biol Phys. 1990 Oct;19(4):1067-70. doi: 10.1016/0360-3016(90)90035-i.
Previous studies showed that the surface heating patterns of the MA-151 applicator on a 2 cm fat and 10 cm thick muscle phantom had center heating at 581 and 930 MHz and two hot spots near the edges of the applicator at 657 and 779 MHz. The hot spots at 657 MHz were consistent with two blisters on a patient's thigh. Since the heating patterns on muscle only showed good center elliptical heating at all frequencies, in this study we have investigated the effects of fat thickness on the heating patterns. Thermograms of fat and muscle surfaces were taken on phantoms with 0, 0.25, 0.5, 1, and 2 cm thick fat exposed to 631 or 915 MHz energy. The 631 MHz was selected to provide reasonable energy coupling for all phantoms. At 631 MHz, two hot spots were evident on all fat surfaces. The pattern on the muscle surface under the 0.25 cm fat did not show two hot spots, but the heating was elongated in the E-field direction. At 915 MHz, the heating was elongated on the surface of the 0.25 and 2 cm fat, and two hot spots were observed on the 0.5 and 1 cm fat surfaces. However, the muscle heating was elliptical in all cases. The ratio of muscle to fat heating decreased as the fat thickness increased. At 0.5 cm fat the ratio was about 1. These results indicate that fat thickness influences heating in muscle. During treatment with this applicator, surface temperature probes should be placed over potential hot spots. Surface cooling is desirable for heating tumors beneath the fat.
先前的研究表明，MA - 151施源器在2厘米厚的脂肪和10厘米厚的肌肉模型上的表面加热模式显示，在581和930兆赫兹时中心加热，在657和779兆赫兹时在施源器边缘附近有两个热点。657兆赫兹处的热点与一名患者大腿上的两个水泡一致。由于肌肉上的加热模式仅在所有频率下均显示出良好的中心椭圆加热，因此在本研究中，我们研究了脂肪厚度对加热模式的影响。在暴露于631或915兆赫兹能量的脂肪厚度分别为0、0.25、0.5、1和2厘米的模型上获取脂肪和肌肉表面的热成像图。选择631兆赫兹是为了为所有模型提供合理的能量耦合。在631兆赫兹时，所有脂肪表面上都明显有两个热点。0.25厘米厚脂肪下的肌肉表面模式未显示出两个热点，但加热在电场方向上拉长。在915兆赫兹时，0.25厘米和2厘米厚脂肪的表面加热被拉长，在0.5厘米和1厘米厚脂肪表面观察到两个热点。然而，在所有情况下肌肉加热都是椭圆形的。肌肉与脂肪加热的比率随着脂肪厚度的增加而降低。在脂肪厚度为0.5厘米时，该比率约为1。这些结果表明脂肪厚度会影响肌肉中的加热。在用这种施源器治疗期间，表面温度探头应放置在潜在的热点上方。对于加热脂肪下方的肿瘤，表面冷却为宜。
