Biomedical Engineering Reference
In-Depth Information
12.3 Clinical applications
Oncology (ECIO). In addition, specialized centers such as the
Center for Image-Guided Interventions (CIGI) at Memorial
Sloan-Kettering Cancer Center in New York City and the Center
for Interventional Oncology at the NIH Clinical Center are
beginning to appear.
Broadly speaking, image-guided minimally invasive cancer
therapy can be grouped within four approaches: ablation, che-
motherapy, radiation therapy, and gene therapy. The focus of
this chapter will be on ablation and chemotherapy applications.
In the remainder of this section we will review the literature in
navigated image-guided cancer therapy for radiofrequency abla-
tion (RFA), cryoablation, and transarterial chemoembolization
(TACE) as follows:
12.3.1 Introduction and Overview
In this section we will describe several clinical applications
where navigation and image guidance have played a major role.
In particular, navigation and image guidance have enabled
minimally invasive approaches to thermal therapy. Although
for many diseases, such as liver tumors, surgical resection and
organ transplantation are seen as the gold standard for curative
therapy, many patients are not candidates for surgery. For liver
metastases alone, only 10-25% of patients are candidates for
resection (Scheele et al. 1995). For the majority of nonsurgical
candidates, image-guided percutaneous ablation is accepted as
the best therapeutic choice. In these patients, thermal therapies
have been proven to be an effective method of palliative care and
improvement of quality of life.
As procedures become more minimally invasive, several dif-
ficulties in visualizing the tumor, planning instrument place-
ment, and prediction of induced necrosis present themselves.
Factors that determine successful clinical outcome are twofold.
Appropriate detection and visualization of the neoplasm and
staging is one concern. Accurate targeting and ablation of the
complete tumor plus a margin is a second concern. The most
critical function of any image-guided approach is to address
these two concerns.
The imaging modality chosen is operator dependent and
based on local availability of dedicated equipment such as
CT and MR systems. Lesions, such as for many primary HCC
that are typically best visualized in arterial-phase CT, would
be hard to identify intra-procedurally. Currently, targeting of
such lesions require mental 3D reconstruction of 2D images
by an interventional radiologist, thus complicating the proce-
dural outcome (Wood et al. 2007). The only imaging modality
that at present has proven real-time intraoperative temperature
monitoring of the efficacy of an ablative treatment is MRI using
special protocols for thermal data acquisition, which can be cost
prohibitive or unavailable in many institutions.
In patients with multiple tumors or where healthy organ vol-
ume is limited, the importance of defining an accurate margin
that encompasses the tumor while sparing as much healthy
tissue as possible is critical. Planning a best path to the tumor
while avoiding critical structures is implicitly more difficult
and assumes greater importance under a minimally invasive
approach. In such cases, the need for preoperative planning is
amplified and some researchers have developed prototype sys-
tems to address this need.
Image-guided cancer intervention is a rapidly developing
field. These procedures are typically done in a multidisciplinary
setting with collaborations between interventional radiolo-
gists, surgeons, hepatologists, oncologists, and other medical
professionals. The increasing interest in this field is evident
through development in the past five years of two related con-
ferences: (1) the World Conference on Interventional Oncology
(WCIO) and (2) the European Conference on Interventional
• Section 12.3.2: Radiofrequency Ablation
• Section 12.3.3: Cryoablation
• Section 12.3.4: Transarterial Chemoembolization
12.3.2 radiofrequency ablation
12.3.2.1 Introduction
Radiofrequency ablation (RFA) is the most widely applied ther-
mal ablation technology with over 100,000 estimated liver abla-
tion procedures performed worldwide (Ahmed et al. 2011). While
many other thermal modalities such as microwave, cyroabla-
tion, high-intensity ultrasound, irreversible electroporation, and
interstitial laser have also evolved, radiofrequency ablation is the
mainstay of most clinical practices and is considered the gold
standard of local ablative therapy for nonresectable liver tumor
patients. RFA has been used successfully in the management
of hepatocellular carcinoma (HCC) (Rossi et al. 1998; Livraghi
et al. 1999), hepatic metastases of colorectal cancer, renal, breast,
osteoid osteomas, and more recently lung neoplasms (Pennathur
et al. 2009). RFA is accepted as the best therapeutic solution for
patients with early stage HCC who would not otherwise qualify
for liver transplantation or surgical resection, or for patients
with metastatic lesions (Crocetti et al. 2010).
An RFA system consists of an RF generator, introducer
trocar needle, and a large dissipative electrode. The RF genera-
tor produces an alternating electric field (< 30MHz; typically
460-480 kHz) across the patient between the electrode pad(s)
placed on the patient skin and the tip of the electrode probe. The
electrode probe is placed within the tumor using ultrasound,
CT, or MR image guidance. The RF signal between the electrode
pad and RF probe causes tissue agitation as a result of oscilla-
tory movement of ions. Tissue heating induces cellular death via
thermal coagulation necrosis.
While earlier probes were monopolar devices, the develop-
ment of multiple hooked (multi-tined) probes (LeVeen
•
needle
electrode) has enabled the ablation of larger lesions (LeVeen
1997; Curley et al. 1999). Probes of this type are the most com-
monly employed for soft-tissue applications today. The probe
consists of multiple curved tines that are deployed from a cen-
tral cannula. Multiple tines help spread the area of coagulation
