Biomedical Engineering Reference
In-Depth Information
11
Endocavity and Catheter-Based
Ultrasound Devices
11.1 Introduction .............................................................................................................................189
11.2 Transrectal Devices for Prostate Thermal Therapy ............................................................189
Transrectal Ultrasound Hyperthermia • Transrectal HIFU for Prostate Therapies
11.3 Transurethral Devices for Prostate Therapy .......................................................................192
11.4 Interstitial and Intraluminal Devices ...................................................................................193
Interstitial with Tubular Sources • Endocervical Devices with Tubular
Sources • Intraluminal Devices with Rotating Planar Sources
11.5 Summary .................................................................................................................................. 196
References ............................................................................................................................................ 196
Chris J. Diederich
University of California,
San Francisco
11.1 Introduction
laser, and cryotherapy technology as currently applied for intersti-
tial and intracavitary hyperthermia and tumor ablation therapies
[3-8]. Furthermore, real-time ultrasound [9-13]and MR imaging
techniques [14-17] can be employed for many of these ultrasound
applicator configurations to monitor thermal therapy and verify
treatment. These advantages and significant potential of ultra-
sound technology for endocavity and catheter-based applications
of thermal therapy are further highlighted in the following sec-
tions, which provide a contemporary and brief review of some
technologies that are commercially available for clinical use or
under development and recently implemented in clinical studies.
In contrast to extracorporeal systems, endocavity and catheter-
based ultrasound devices have been developed for delivering
hyperthermia and thermal ablation from placement within the
body. These minimally invasive ultrasound techniques can be
used to apply hyperthermia as an adjunct to radiation therapy
and/or chemotherapy, or as a surgical alternative for tumor or
tissue ablation. For these applications, the heating source is posi-
tioned directly within or adjacent to a deep target volume via
placement within a body cavity, lumen, or by direct insertion.
Even though these technologies are more invasive than extra-
corporeal systems, many of these approaches may be preferable
for sites where energy localization from external devices is dif-
ficult or where localization of all power and energy propagation
within the target tissue is critical.
There are many physical properties of ultrasound that make it
a favorable energy modality for applications in this setting [1,2]:
small wavelengths in the 1-15 MHz range combined with an abil-
ity to shape transducers or phased arrays yield small energy radi-
ating platforms capable of precise and predictable spatial control
of power deposition; favorable energy penetration and focusing
capabilities allow therapeutic heating at distances away from the
applicator, and opportunity to heat larger volumes quickly while
protecting intervening tissues. Thus, in clinical practice, many
of these ultrasound devices can selectively direct or conform
the heating volume to a specified target area while protecting or
avoiding other tissues. This enhanced spatial localization and
energy penetration provides ultrasound with a significant advan-
tage over the radio-frequency (RF) currents, microwave (MW),
11.2 transrectal Devices for
prostate thermal therapy
11.2.1 transrectal Ultrasound Hyperthermia
Intracavitary ultrasound applicators specifically for delivering
prostate hyperthermia from within the rectum have been devel-
oped and used successfully in clinical treatments [18,19]. Original
applicators consist of a linear segmented array (4-8) of sectioned
PZT tubes (180° sections, 10 mm long, 1.5 cm OD), each under
separate power control and operating between 1 MHz and 2 MHz
[20]. The transducers are mounted on a plastic structure that
facilitates support and placement in the rectum, as well as temper-
ature-regulated water flow within an expandable bolus. The cylin-
drical ultrasound transducers are sectored to shape and direct
the heating field in an ~120° arc to the target volume. The heating
energy is emitted radially from the length of each transducer seg-
ment and the power applied along the length of the applicator is
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