Biomedical Engineering Reference
In-Depth Information
(a)
(b)
FIGURE 8.16
Sigma Eye applicator (a) as implemented in the hyperplan treatment planning software, (b) the most recent version for clinical use.
to achieve maximum constructive interference at the site of the
target position.
The Sigma 60-E (ellipse) differs only form the Sigma 60 in the
fact that the Lucite cylinder is replaced by an octagonal-shaped
Lucite container. The lower height of water above the abdo-
men should reduce water pressure and improve patient comfort.
Fatehi et al. [80] demonstrate that at the lower frequencies of 75
to 90 MHz and at 100 MHz the SAR characteristics of the Sigma
60-E are almost identical to those of the Sigma-60 and Sigma Eye
applicators, respectively.
8.5.2.2.2 BSD-2000/3D and BSD-2000/3D/MR
The addition of phase and amplitude control to the Sigma-60
applicator has proven its clinical utility to modify the SAR dis-
tribution in relation to patient complaints. However, when the
aim is more specific, such as to increase a local target tempera-
ture, a quantum step toward improved SAR steering is required
[81]. The Sigma Eye applicator was developed to provide this next
level in three-dimensional power deposition at depth (see Figure
8.16). The Sigma Eye is eye-shaped and operates at 100 MHz, but
includes three rings of eight dipoles each. With 12 independent
phase and amplitude adjustments, it offers superior versatility to
shape and steer power deposition peaks both axially and radially
around the body interior. Furthermore, the Sigma Eye applicator
provides an improved water bolus design (i.e., the length of the
water bolus has been increased to provide contact with nearly the
entire surface of the patient's body within the array). This pre-
vents concentration of energy at the contacting edge of the water
bolus. The Sigma Eye water bolus thickness, above the anterior
patient's surface, is half to one-third that of the Sigma 60 bolus,
which is expected to significantly improve patient comfort.
In several theoretical studies [69,70,71,72] the performance of
the Sigma Eye applicator has been demonstrated to be superior to
the Sigma-60 applicator in terms of ability to focus energy to the
target and to obtain higher tumor temperatures. Canters et al. [82]
demonstrated for 10 patients with locally advanced cervical can-
cer that use of the Sigma Eye with optimized phase and amplitude
settings results in 8 of 10 patients with substantial higher tempera-
ture increase (Sigma Eye temperature is on average 1.5°C higher),
in 1 of 10 patients no change, and in 1 of 10 patients with lower
temperatures. In line with Seebass et al. [71], the data of Canters
et al. [82] show that the increased number of degrees of freedom
of the Sigma Eye applicator translates in a higher gain potential
of SAR targeting. However, in order to exploit this potential it is
essential to find a solution for the accurate matching of the phase
and amplitude used in the model to that applied in reality at the
antenna feed points of the Sigma Eye applicator.
The BSD-2000/3D/MR is always delivered with the 12-chan-
nel Dodek amplifier with integrated phase-locked loop systems
for accurate control of the phase and amplitude settings.
The improved 3D steering is particularly useful when imple-
mented with a magnetic resonance system that is capable of
noninvasive 3D imaging showing the temperature distribution
in the heated regions [83]. The latter permits the 3D steering
to more accurately target the energy to the tumor site. Using
sophisticated microwave filtering and imaging software, the
BSD-2000/3D/MR (Figure 8.17) allows an MRI system to be
interfaced with and operate simultaneously with a BSD-2000/3D
(BSD Medical Corporation). The MRI compatible version of
the system facilitates pretreatment planning as well as real-
time MRI monitoring of deep tissue temperature, perfusion,
necrosis, and chemical changes during treatment [84,85,86].
Various temperature-sensitive MRI parameters exist and can
be exploited for MR temperature mapping. The most popu-
lar parameters are proton resonance frequency shift, diffusion
FIGURE 8.17
The BSD-2000/3D/MR system for loco-regional hyper-
thermia with simultaneous noninvasive temperature monitoring by
MRI.
