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Hyperthermia and ablation 267

Figure 8.11 Basic models of array MW pin-applicators inserted in the target tissue (here, in the
shape of a cylinder); the models are built for FEM numerical analysis (Morega et al., 2014, 2015a).
FEM, Finite element method.

characteristics were examined in the study of Morega et al., (2008, 2014). Although
they provide a good technical solution to the temperature control problem (i.e., the
possibility of uniformly heating a predetermined volume) (Ito et al., 2001; Morega
et al., 2006; Saito et al., 2004), the array applicators come with the disadvantage of
increased discomfort or pain for the patient and contingent tissue damage through
bleeding and swelling (NIH); however, these inconveniencies are temporary whereas
the proceedings might be decisive.
The optimal design of the applicator translates here in choosing the best number of
components and the spacing between adjacent pins, conditions correlated with the
particular electrical and thermal behavior of the tissue, expressed by its physical proper-
ties for the specific operating frequency and temperature range (Andreuccetti et al.,
1997; Rosmann; Karampatzakis et al., 2013). The efficiency of the procedure is fur-
thermore conditioned by other characteristics of the electromagnetic radiation source:
waveform, power, phase-shift between individual pin emissions. Various combinations
could be tested and assessed with the help of an experimental model and even better
by numerical simulation. A numerical analysis was performed that way and the optimal
configuration for a three-pin applicator is shown in (Morega et al., 2006). Figure 8.12
illustrates, for comparison, the temperature distributions for a single-pin versus a three-
pins array applicator (same pin design), aimed for mild interstitial hyperthermia, but
scalable for ablation too.
For the three-pins array, the distance between adjacent pins was determined after
an optimization study, and it leads to an almost uniform temperature distribution in
the tissue encompassed by the pins. The three-pins are positioned at the vertices of an
3
equilateral triangle at 13 mm distance; the tissue volume of approx. 1,150 mm is

quasi-uniformly heated (42 C 43 C) within the therapeutic temperature range for

mild hyperthermia (Morega et al., 2006).