Paulides M M, Wielheesen D H M, Van der Zee J, Van Rhoon G C
Department of Radiation Oncology, Section Hyperthermia, Erasmus MC, Daniel den Hoed Cancer Center, PO box 5201, NL-3008 AE, Rotterdam, The Netherlands.
Int J Hyperthermia. 2005 Mar;21(2):125-40. doi: 10.1080/02656730400013855.
The objective of this work is to gain insight in the distortions on the local SAR distribution by various major anatomical structures in the neck. High resolution 3D FDTD calculations based on a variable grid are made for a semi-3D generic phantom based on average dimensions obtained from CT-derived human data and in which simplified structures representing trachea, cartilage, spine and spinal cord are inserted. In addition, phantoms with dimensions equal to maximum and minimum values within the CT-derived data are also studied. In all cases, the phantoms are exposed to a circular coherent array of eight dipoles within a water bolus and driven at 433 MHz. Comparisons of the SAR distributions due to individual structures or a combination of structures are made relative to a cylindrical phantom with muscle properties. The calculations predict a centrally located region of high SAR within all neck phantoms. This focal region, expressed as contours at either 50% or 75% of the peak SAR, changes from a circular cross-section in the case of the muscle phantom to a doughnut shaped region when the anatomical structures are present. The presence of the spine causes the greatest change in the SAR distribution, followed closely by the trachea. Global changes in the mean SAR relative to the uniform phantom are <11%, whilst local changes are as high as 2.7-fold. There is little difference in the focal dimensions between the average and smallest phantoms, but a decrease in the focal region is seen in the case of the largest phantom. This study presents a first step towards understanding of the complex influences of the various parameters on the SAR pattern which will facilitate the design of a site-specific head and neck hyperthermia applicator.
这项工作的目的是深入了解颈部各种主要解剖结构对局部比吸收率（SAR）分布的畸变情况。基于从CT衍生的人体数据获得的平均尺寸，对一个半三维通用体模进行了基于可变网格的高分辨率三维时域有限差分（FDTD）计算，并在其中插入了代表气管、软骨、脊柱和脊髓的简化结构。此外，还研究了尺寸等于CT衍生数据中最大值和最小值的体模。在所有情况下，体模都置于水囊内的一个由八个偶极子组成的圆形相干阵列中，并以433MHz的频率驱动。将由于单个结构或结构组合导致的SAR分布与具有肌肉特性的圆柱形体模进行比较。计算结果预测，所有颈部体模内都有一个位于中心的高SAR区域。这个焦点区域，以峰值SAR的50%或75%处的等高线表示，在肌肉体模的情况下从圆形横截面变为存在解剖结构时的甜甜圈形状区域。脊柱的存在导致SAR分布变化最大，其次是气管。相对于均匀体模，平均SAR的全局变化<11%，而局部变化高达2.7倍。平均体模和最小体模之间的焦点尺寸差异不大，但最大体模的焦点区域有所减小。这项研究朝着理解各种参数对SAR模式的复杂影响迈出了第一步，这将有助于设计针对特定部位的头颈热疗施加器。
