Moros E G, Myerson R J, Straube W L
Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Med Phys. 1993 Sep-Oct;20(5):1399-409. doi: 10.1118/1.597125.
Three-dimensional acoustic and thermal models were developed to simulate superficial hyperthermia treatments using a new multielement planar ultrasonic system. Typical power density and steady-state temperature distributions are presented. A parametric study was performed to determine the relationship between therapeutic volume (volume at and above 42 degrees C) and aperture size (number of active elements). The parameters investigated were: maximum allowable temperature, skin surface temperature, blood perfusion (thermal diffusion length), acoustic absorption, and frequency. Results showed that this device produces well distributed sound beams with lateral dimensions comparable to the aperture size. These simulated results were in agreement with experimental measurements. The simulated temperature distributions were uniform at each depth across the applicator's aperture. The main heating characteristics found were: (1) the therapeutic volume was directly proportional to the aperture size; (2) the lateral dimensions of the therapeutic volume were independent of the parameters studied and remained practically constant with depth for several centimeters, with a very rapid increase near the skin surface and a very rapid fall off at depth; and (3) therapeutic penetration was strongly dependent on maximum allowable temperature, frequency, and acoustic absorption; and weakly dependent on blood perfusion and skin surface temperature. These heating characteristics are new in commercial systems for superficial hyperthermia. Despite the well-distributed beams, it was found that in order to produce adequate hyperthermia with this device the lateral dimensions of tumors must be smaller than the applicator's active aperture and that thermal depth coverage must be monitored during treatments. Guidelines for aperture selection and thermometry strategies are discussed.
开发了三维声学和热模型，以模拟使用新型多元素平面超声系统进行的浅表热疗治疗。给出了典型的功率密度和稳态温度分布。进行了参数研究，以确定治疗体积（42摄氏度及以上的体积）与孔径大小（有源元件数量）之间的关系。研究的参数包括：最高允许温度、皮肤表面温度、血液灌注（热扩散长度）、声吸收和频率。结果表明，该设备产生的声束分布良好，其横向尺寸与孔径大小相当。这些模拟结果与实验测量结果一致。在整个施加器孔径的每个深度处，模拟的温度分布都是均匀的。发现的主要加热特性如下：（1）治疗体积与孔径大小成正比；（2）治疗体积的横向尺寸与所研究的参数无关，在几厘米的深度范围内基本保持恒定，在皮肤表面附近迅速增加，在深度处迅速下降；（3）治疗穿透深度强烈依赖于最高允许温度、频率和声吸收；而对血液灌注和皮肤表面温度的依赖性较弱。这些加热特性在商业浅表热疗系统中是新的。尽管声束分布良好，但发现为了使用该设备产生足够的热疗，肿瘤的横向尺寸必须小于施加器的有源孔径，并且在治疗过程中必须监测热深度覆盖情况。讨论了孔径选择和测温策略的指导原则。
