Biomedical Engineering Reference
In-Depth Information
The general advantages of these devices noted for hyper-
thermia are also applicable for percutaneous thermal ablation
whereby high temperature alone is used to destroy the tumor or
target region. Demonstration of capabilities include substantial
size thermal lesions
in vivo
[63,66,68,71] up to 21-25 mm
radial
distance from the applicator, within 5 min treatment times,
while maintaining axial and angular control of lesion shape
[72]. Furthermore, these devices are MRI compatible, and abil-
ity to monitor temperature elevation in real time using MRTI
has been demonstrated
in vivo
[71,73]. Although not applied in
clinical study as yet for thermal ablation, there are significant
advantages such as dynamic spatial control in angle and length,
penetration, and compatibility with MRTI that are currently
being explored.
segments (2-3 transducers, 3.5 mm diameter × 10 mm length
each) can be activated to tailor heating to target regions at the cer-
vix. Water cooling is applied for coupling and improved penetra-
tion. In contrast to the smaller interstitial devices, each of these
larger tubes can have multiple sectors that can be independently
activated (dual 180° activation typical). For devices using tubular
transducers with multiple sectors, there are ~20-30° dead zones
without acoustic energy output between each of the active sec-
tors. For treatment of the cervical cancer, the bladder and rectum
often confine the anterior and posterior treatment borders close
to the cervix. The active portions can be directed laterally into the
parametrium and power adjusted to extend penetration, while
the acoustic dead zones between active sectors can be used to
afford less heating to the thermally sensitive bladder and rectum.
Studies have demonstrated the capabilities of these devices to gen-
erate shaped and penetrating heating patterns around the cervix
extending >2 cm radial [74], and in practice they can be combined
with interstitial to further boost regions of heating outside of the
cervix [75] (as depicted in Figure 11.6 c).
11.4.2 Endocervical Devices with
tubular Sources
An endocervical ultrasound applicator has been designed spe-
cifically for delivering hyperthermia to the uterine cervix and
surrounding target regions [74]. The desired treatment region is
typically 2-3 cm in length along the cervix and 2-4 cm diameter
with lateral extension typical. These endocavity or intrauterine
applicators (Figure 11.6a) are designed to be placed within the
HDR brachytherapy tandem catheter (6 mm diameter) that is
typically placed within the uterine cervix either through a ring
applicator or a vaginal cylinder. Multiple tubular transducer
11.4.3 Intraluminal Devices with
rotating planar Sources
Intraluminal ultrasound applicators (3.8-4.0 mm OD) that
utilize planar ultrasound transducer segments with rotational
transducer control have been devised in efforts by Lafon et al.
[76-79] and Chopra et al. [53], including a design that enables
RF power connectors
(a)
Brachy ring
Dual sector
tubular array
PET
catheter
Cooling flow hub
(b)
(c)
43.3°C
42.5°C
Bladder
41.8°C
39.9°C
CTV
43.2°C
41.9°C
38.9°C
38.8°C
42.5°C
42.8ºC
HTV
30 mm
30 mm
FIGURE 11.6
(a) Endocervical ultrasound applicator within tandem catheter and ring applicator as integrated system for HDR brachytherapy
combined with hyperthermia; (b) dual-directional applicator within cervix is positioned to preferentially direct heating laterally extending 2 cm
radially; (c) addition of 360° interstitial applicator in periphery further extends heating penetration. Inner contour is the hyperthermia target zone
(HTV). Steady-state temperatures measured mid-target are labeled.
