Biomedical Engineering Reference
In-Depth Information
margin of healthy tissue. However, the definition of an adequate
tumor-free margin varies with the type of malignant tumor. For
instance, the surgical margin in hepatic resection for colorectal
metastasis was defined as being, preferably, 2 cm but no less than
1 cm of normal liver [95]. If the objective of HIFU is to repli-
cate the success of liver resection, the same tumor-free margin
should be treated.
The other goal of HIFU treatment is palliative for patients
with advanced-stage cancer. They are usually those who have an
unresectable tumor and for whom conventional tumor thera-
pies, including chemotherapy and radiotherapy, have failed to
control tumor growth. HIFU can be clinically used to impede
tumor growth and improve the quality of life for such patients.
Among those treated with HIFU in China, most are advanced-
stage patients who are beyond the scope of conventional treat-
ments. In these circumstances, HIFU can be successfully
performed as a palliative method using partial or complete abla-
tion. Symptoms such as pain caused by tumor disappear after
HIFU, and survival time can be extended
.
nature of HIFU, and there is an increasing body of work describ-
ing HIFU in the treatment of both primary and secondary liver
cancer in human clinical trials.
In the early 1990s, Vallancien et al. [101] treated two patients
with liver metastases prior to surgical resection; in one there
was no visible effect, and in the other there was extensive tis-
sue laceration and patchy necrosis. In 2001, we reported for the
first time that HIFU could successfully treat patients with pri-
mary liver cancer, and a demarcated coagulation necrosis was
clearly detected by pathological examinations in the HIFU-
treated HCC [102]. From March 1998 to October 2001, a total
of 474 patients with liver cancer, including primary and meta-
static liver cancer, received HIFU treatment at ten hospitals in
China [93].
Almost all patients had unresectable HCC ranging
from 4 to 15 cm in diameter. Among them, most patients were
advanced-stage patients with hepatic cirrhosis, and HIFU was
used as a palliative therapy in clinical practice.
Wu et al. [103] reported a prospective, nonrandomized clinical
trial in which 55 HCC patients with cirrhosis were treated with
USgHIFU therapy in Chongqing, China. Of these, 51 patients
had unresectable HCC, and tumor size ranged from 4 to 14 cm
in diameter with mean diameter of 8.14 cm. The results showed
that HIFU was safe, and no severe side effects were observed after
the treatment. The overall survival rates at 6, 12, and 18 months
were 86.1%, 61.5%, and 35.3%, respectively. The survival rates
were significantly higher in patients in stage II than those in stage
III
A
(
P
< 0.0132) and in stage III
C
(
P
< 0.0265). From November
1998 to May 2000, 50 consecutive patients with stage IV
A
HCC
were enrolled in a randomized, controlled clinical trial to assess
the local therapeutic efficacy of USgHIFU therapy combined with
transcatheter arterial chemoembolization (TACE) and TACE
alone [104]. These patients were divided into two groups: TACE
alone was performed in group 1 (n = 26), and HIFU combined
with TACE was performed in group 2 (n = 24). Tumors ranged
from 4-14 cm in diameter (mean 10.5 cm). Follow-up images
showed absence or reduction of blood supply in the lesions after
HIFU ablation when compared with those after TACE alone. The
median survival times for patients were 11.3 months in the group
2 and 4 months in the group 1 (
P
= 0.0042). The 6-month survival
rate of patients was 80.4-85.4% in group 2 and 13.2% in group
1 (
P
= 0.0029), and the 1-year survival rate was 42.9% and 0%,
respectively (
P
< 0.01). Li et al. [105] also reported similar results
of HIFU combined with TACE for 89 patients with large unresect-
able HCC. Follow-up results showed that 1-5 year overall survival
rates were much higher in the HIFU combined TACE group than
those in the TACE group. Recently, Zhang et al. [106] reported
effects of HIFU ablation on 39 HCC patients whose lesions were
close to the major hepatic blood vessels. Although the distance
between tumor and main blood vessel was less than 1 cm, HIFU
could achieve complete coagulation necrosis of HCC lesions,
with no evidence of discernible damage to the major vessels in
all patients. In addition, HIFU could be successfully used to treat
needle-track seeding of HCC
[107]. The results showed that during
a mean follow-up of 10 months, complete ablation was persistently
observed in eight patients, but one patient developed a recurrent
15.7.2 anesthesia Selection for HIFU therapy
Almost all patients have an uncomfortable sense of pain origi-
nating from the targeted tissue during HIFU procedures. Also, it
is almost impossible for them to tolerate one fixed position with-
out any motion for a long time. Therefore, either local or general
anesthesia, as well as sedation, is essential to HIFU treatment.
The selective standard of anesthesia is dependent on two factors.
(1) The most important is the patient's general condition that
decides which kind of anesthesia is suitable, and how far the tar-
geted organ can move. (2) If clinical examinations show that the
patient is able to receive any kind of anesthesia, the movement
of the targeted organ becomes the dominant factor to influence
the decision made by an anesthetist who is experienced in col-
laborating with HIFU doctors.
The anesthetist selects the anesthetic, primarily on the basis
of targeted organ motion, ablation time, patient position, tumor
location, and therapeutic ultrasound exposure. General anesthe-
sia is usually used to ensure immobilization of targeted organs
such as liver, kidney, and pancreas during the HIFU procedure.
Endotracheal intubation and mechanical ventilation enables
single lung ventilation on one side and, therefore, controls
the movement of these organs, which is caused by respiration.
Furthermore, it has the supplementary benefit of permitting
temporary suspension of respiration with controlled pulmonary
inflation, as necessary, to ablate a liver or kidney tumor behind
the ribs.
15.7.3 HIFU therapy for Liver Cancer
Because hepatocellular carcinoma (HCC) is frequently seen in
the setting of hepatic cirrhosis, surgery can be performed in only
10% to 20% of patients with HCC [96-100]. Most HCC patients
lose the chance to be treated with surgery. So the liver has been a
major target of HIFU for a long time because of the noninvasive
