Biomedical Engineering Reference
In-Depth Information
FIGURE 8.18
First version of the HYPERcollar applicator for hyperthermia of head and neck tumors [89].
coefficient D, longitudinal relaxation time T(1), and equilibrium
magnetization M(0) [87]. The correlation of noninvasive MR
thermography with direct tumor temperature measurements
and clinical response has been demonstrated in clinical results
[88]. Together, the BSD-2000/3D/MR offers optimized patient
safety and easier hyperthermia treatment since there is no need
for invasive thermometry catheters.
200 W per channel. The power setting is applied with a precision
of 2 W and for the phase it is smaller than 0.1 degree [91].
The HYPERcollar is able to generate a central 50% iso-SAR
focus of 35 ± 3 mm in diameter and about 100 ± 15 mm in length
under clinical conditions. This SAR focus can be steered toward
the desired location in the radial and axial directions with an
accuracy of ~5 mm.
In a critical review Paulides et al. [92] reported on their first
clinical experiences and demonstrate the pivotal role of hyper-
thermia treatment planning. Three representative patient cases
(thyroid, oropharynx, and nasal cavity) were discussed. They
reported that hyperthermia treatments for these tumor loca-
tions in the head and neck region, lasting as long as 1 h, were
feasible and well tolerated and no acute treatment-related toxic-
ity was observed. Maximum temperatures measured were in the
range of those obtained during deep hyperthermia treatments in
the pelvic region, but there is still ample room to improve mean
temperatures. Further, they found that simulated power absorp-
tion correlated well with measured temperatures, illustrating
the validity of a treatment approach of using energy profile opti-
mizations to arrive at higher temperatures.
8.5.2.2.3 The HYPERcollar Loco-Regional Hyperthermia System
The HYPERcollar loco-regional hyperthermia system has been
especially developed to provide adequate heating of tumors
located centrally in the head and neck region. The design
of the HYPERcollar differs from previous applicator design
approaches in the fact that it was inversely developed. First, the
target volume to be heated was defined, and then the applicator
was designed by theoretically using advanced electromagnetic
modeling. An important feature of such an approach is that a
priori the translation of a predicted SAR distribution has a high
probability to resemble the actual SAR distribution in vivo.
The HYPERcollar consists of a transparent Lucite cylinder
(radius 40 cm, height 15 cm) covered with a fine conducting
gauze forming the conducting backplanes required for the patch
antennas (see Figure 8.18). Twelve probe-fed patch antennas are
mounted in two rings [89] on the Lucite cylinder. The distance
between the center planes of the two antenna rings is 6 cm. Details
of the dimensions of the patch can be found in [90]. The entire
applicator is attached to a movable trolley and can be rotated
around the z-axis (patient-axis) and around the x-axis (left-right)
for maximum positioning flexibility. An inflatable water bolus
is attached to the Lucite cylinder for cooling of the skin and to
enable an efficient transfer of the electromagnetic waves from the
antennas into the patient. The system is equipped with 12 amplifi-
ers with either incoherent or phase-controlled coherent 434 MHz
signals. The maximum power at the antenna feeding points is
8.6 Summary and Future Directions
Considering the inexistence of specific hyperthermia equipment
in the 1980s, it is fair to conclude that hyperthermia technology
has come a long way. The currently available commercial and
academic systems represent solid approaches for the clinical
application of superficial and loco-regional hyperthermia with a
good control of the heating quality.
The development of multi-element array applicators has
brought a major improvement in the spatial control of energy
deposition for both superficial and loco-regional hyperthermia.
Impressive progress has also been made with regard to efficiency
