Gellermann Johanna, Göke Jonathan, Figiel Robert, Weihrauch Mirko, Cho Chie Hee, Budach Volker, Felix Roland, Wust Peter
Clinic for Radiation Medicine, Charité Medical School, Campus Berlin Buch, Lindenberger Weg 80, 13125 Berlin, Germany.
Int J Hyperthermia. 2007 Feb;23(1):37-47. doi: 10.1080/02656730601121549.
Proximally located presacral recurrences of rectal carcinomas are known to be difficult to heat due to the complex anatomy of the pelvis, which reflect, shield and diffract the power. This study is to clarify whether a change of position of the Sigma-Eye applicator in this region can improve the heating.
Finite element (FE) planning calculations were made for a phantom model with a proximal presacral tumour using a fixed 100 MHz radiofrequency radiation. Shifts of the applicator were simulated in 1 cm steps in x-(lateral), y-(posterior) and z-(longitudinal) direction. Computations also considered the network effects of the Sigma-Eye applicator. Optimisation of the phases and amplitudes for all positions were performed after solving the bioheat-transfer-equation. The parameters T90, T50, sensitivity, hot spot volume and total deposited power have been sampled for every applicator position with optimised plans and a standard plan.
The ability to heat a presacral tumour clearly depends on the applicator position, for standard antenna adjustment and also for optimised steering of the Sigma-Eye applicator. The gamma-direction (anterior-posterior) is very sensitive. Using optimised steering for each position, in z-direction (longitudinal), we found an unexpected additional optimum at 8 cm cranial from the middle position of the phantom. The x-direction (lateral) is in a clinical setting less important and shows only smaller changes of T90 with an expected optimum in the central position. A positioning of the applicator in the axial and anterior position of the mid-pubic symphysis should be avoided for treatment of the presacral region, regardless of the used adjustment. Use of amplitude and phase optimisation yields better T90 values than plans optimised only by phases, but they are much more sensitive for small variations of phases and amplitudes during a treatment, and the total power of the Sigma-Eye applicator can be restricted by the treatment software.
Complex geometry of the human pelvis seems to be the reason for the difficulties to warm up the proximal presacral region. The assumption that every position can be balanced by a proper phase adaption, is true only in a small range. A centring of the applicator on the mid-pubic symphysis to heat this region should be avoided. From the practical point of view improved warming should be performed by optimisation of phases only.
由于骨盆复杂的解剖结构，直肠癌骶前近端复发灶难以加热，这种解剖结构会反射、屏蔽和散射能量。本研究旨在阐明Sigma-Eye applicator在该区域位置的改变是否能改善加热效果。
使用固定的100MHz射频辐射，对一个具有骶前近端肿瘤的体模模型进行有限元（FE）规划计算。在x轴（横向）、y轴（后方）和z轴（纵向）方向以1cm步长模拟applicator的移位。计算还考虑了Sigma-Eye applicator的网络效应。在求解生物热传递方程后，对所有位置的相位和幅度进行优化。对于每个applicator位置，采用优化计划和标准计划对参数T90、T50、敏感度、热点体积和总沉积功率进行采样。
加热骶前肿瘤的能力明显取决于applicator的位置，这对于标准天线调整以及Sigma-Eye applicator的优化操控均适用。γ方向（前后方向）非常敏感。在z轴（纵向）方向，对每个位置采用优化操控时，我们在距体模中间位置颅侧8cm处发现了一个意外的额外最优位置。在临床环境中，x轴（横向）方向不太重要，T90的变化较小，预期最优位置在中心位置。无论采用何种调整方式，治疗骶前区域时应避免将applicator放置在耻骨联合中部的轴向和前方位置。与仅通过相位优化的计划相比，使用幅度和相位优化可产生更好的T90值，但在治疗过程中，它们对相位和幅度的微小变化更为敏感，并且Sigma-Eye applicator的总功率可能会受到治疗软件的限制。
人体骨盆复杂的几何结构似乎是骶前近端区域难以加热的原因。认为每个位置都可通过适当的相位适配达到平衡的假设，仅在小范围内成立。应避免将applicator对准耻骨联合中部来加热该区域。从实际角度来看，仅通过相位优化即可改善加热效果。
