Biomedical Engineering Reference
In-Depth Information
FIGURE 8.12
The AMC-8 phased-array waveguide system. The system consists of two rings of four waveguides operating at 70 MHz. Every
waveguide has a separate water bolus that provides superficial cooling of the patient and coupling of the incident electromagnetic field into the
patient. The two bottom waveguides share the same water bolus. The distance between the two rings is adjustable [73,74].
Ring-to-ring distance is of minor importance but should be
known for proper optimization within 2 cm. For the AMC-8
system, the achievable thermal dose is stable over a range of
−8 cm to +8 cm shiting the patient in the caudal −cranial direc-
tion. Axial position should be known within 1 −2 cm both for
the AMC-4 and the AMC-8 system.
A special feature of the design of the AMC-4 waveguide sys-
tem is that the waveguide applicator has a relatively small width.
Consequently, the overlap of the waveguide aperture in rela-
tion to the target volume is very limited in comparison with, for
instance, the Sigma-60 applicator. Clinically, this feature is very
important when heating tumors in the upper thorax; it allows
heating of esophageal tumors with the AMC-4 loco-regional
hyperthermia system [66,76].
Sigma Treatment Base Unit includes both patient and applicator
support systems. The patient is placed on the sling in preparation
for the therapy, then the applicator is positioned over the tumor
area and the water bolus filled. A large water reservoir mounted in
the base unit maintains the bolus water at the desired temperature
throughout the treatment.
For temperature measurement the BSD-2000 system is equipped
with eight Bowman thermometers. Due to the high resistance car-
bon wires the Bowman probes are transparent for the electromag-
netic field, and hence temperature measurement is continuous. In
addition the system can be extended with eight probes to measure
the external electrical field (E-field) at the surface of the patient
body. This option is, however, used by only a few centers.
The BSD-2000 family of applicators includes the Sigma 60,
Sigma 40, Sigma 30, and the Sigma 60-E (see Figures 8.13 and
8.14). The Sigma 30- to Sigma-60 applicators consist of a Lucite
cylinder with integrated water bolus and four sets of dual dipole
antennas mounted on the inner side of the cylinder (an antenna
consists of two identical dipole arms built from tapered copper
that are glued to the Lucite cylinder wall). The dipole is designed
to operate in water and the dielectric contrast seen by the dipole
(water on one side and air/Lucite on the backside) causes the
dipole to emit the energy preferentially to the patient (and to
keep stray radiation at an acceptable level). The water bolus
serves also to cool the skin surface. The various applicators pro-
vide the opportunity to select an applicator size in accordance
with treatment region, for example, for children and adults.
The BSD-2000 provides the possibility of SAR steering by
phase and amplitude control, and by SAR steering the maxi-
mum energy deposition can be moved from the center of the
body to the periphery (2D-SAR steering) [78]. Extensive char-
acterization of the performance of the Sigma-60 applicator
8.5.2.2 the BSD-2000* Family of Loco-
regional Hyperthermia System
8.5.2.2.1 BSD-2000
The BSD-2000 system [77] is the most common deep hyperther-
mia system in clinical use and is available with the Tetra or Dodek
amplifier set. The TETRA 4-channel solid-state amplifier oper-
ates in the frequency range of 75 to 140 MHz and delivers up to
1200 W to the applicator. The Dodek amplifier is a 12-channel
solid-state amplifier with typically 150 W per single channel, total
power 1800 W, over a frequency range of 50−250 MHz. When the
Dodek amplifier is used in combination with a 4-channel applica-
tor, the power output of three single channels is combined with
an RF-power combiner and fed into the dual-dipole antenna. The
*
he BSD-2000, BSD-2000/3D, and the BSD-2000/3D/MR are not approved
by the FDA for any kind of use within the United States.
