Biomedical Engineering Reference
In-Depth Information
Furthermore, DSA can clearly show variants of regional blood
supply in the treated tumor after HIFU ablation. Because of inter-
ventional examination, applications of DSA are relatively limited.
As a physiological imaging, SPECT can provide tomographic
images of the radioactivity distribution in a small number of
tumors such as osteosarcoma. However, it does not clearly identify
the therapeutic response in most tumors, particularly in patients
with liver cancer. Theoretically, PET can be employed to detect
physiological function in almost solid malignancies.
Non-enhanced CT obtained 1-2 weeks after HIFU ablation is
not sufficiently sensitive to assess therapeutic response, especially
in encapsulated lesions such as those of hepatocellular carcinoma,
and of osteosarcoma lesions located in the long bone marrow cavity.
However, non-enhanced MRI may characteristically reveal varied
signals of ablated tumors on both T1- and T2-weighted images after
HIFU ablation. Contrast-enhanced CT is useful for demonstrating
changes in tumor vascular perfusion, and for distinguishing the
difference between nonviable and residual viable tumor directly
in the treated regions. The most striking changes are seen in con-
trast-enhanced MRI, where it is common to observe the absence
of contrast enhancement in the treated tumors that originate from
liver, pancreas, kidney, breast, bone, soft tissue, and uterus. Areas of
hypoattenuation, shown on MRI or CT, that did not enhance after
contrast material administration can be considered to represent
necrotic tissue. Still-enhancing areas are assumed to reveal residual
viable tumor. In addition, a thin peripheral rim of enhancement
may be detected surrounding the coagulation necrosis. This densely
enhancing peripheral rim on delayed contrast imaging should not
be misconstrued as residual tumor. In fact, this rim represents an
inflammatory reaction to thermal ablation. However, a thick irregu-
lar rim at the edge of a treatment site is the most common feature
of partial thermal ablation. In conclusion, among the follow-up
images, enhanced CT or MRI should be standard imaging criteria
for response assessment of treated tumors after HIFU ablation.
There is a lack of consensus on a standard regimen for follow-
up imaging. Our clinical experience shows that diagnostic images,
particularly enhanced MRI or CT, can be used to assess the efficacy
of HIFU therapy 1-2 weeks afterwards. In addition to reporting
tumor size and the diameter of the ablation volume, assessment
of contrast enhancement or lack in the treated tumor can provide
imaging information about tumor response and residual live tumor
cells after HIFU ablation. Follow-up imaging at 3 months is neces-
sary to detect new-growth tumors in untreated regions. Imaging
at 6-12 months can show obvious regression of the lesion and the
region of coagulation necrosis. Most frequently, the treated volume
without blood supply shrinks by less than 20-50% in volume.
in animals. The recent resurgence of this noninvasive therapy
is driven by the advances in the development of medical imag-
ing techniques, which makes it possible to target HIFU extra-
corporeally and precisely ablate a tumor at depth. To date, two
extracorporeal HIFU devices have been clinically used world-
wide. They incorporate either MRI or B-mode ultrasonogra-
phy to monitor the therapeutic procedure. The advantages and
limitations of both imaging modalities used in HIFU have been
described in Section 15.6, “Medical Imaging in HIFU Ablation.”
Clinical applications of the extracorporeal USgHIFU device
follow.
Extracorporeal USgHIFU has been widely used for the treat-
ment of solid tumor in China since 1999. The malignancies
treated with HIFU include those of the liver, breast, kidney, pan-
creas, soft tissue, and bone; the benign tumors treated include
uterine fibroids and breast fibroadenomas [93]. Most of these
clinical applications present encouraging short-term outcomes;
long-term follow-up survival data are now emerging for the
treatment of hepatocellular carcinoma, breast cancer, and osteo-
sarcoma. As large numbers of patients with solid malignancy are
treated in China, the clinical experiences with extracorporeal
USgHIFU are very important and should be shared worldwide.
Much of the material of Section 15.7 is about the clinical knowl-
edge and practice of HIFU in China; it is not intended to be
exhaustive but to serve as an illustration of our clinical experi-
ence to date. Much of the clinical application is very recent, and
detailed survival data will follow in subsequent publications.
15.7.1 purposes of HIFU therapy
In practice, cancer therapy usually needs to have multiple treat-
ment methods for long-term survival benefit in addition to local
therapy such as surgery. For instance, in the treatment of patients
with breast cancer, surgery, chemotherapy, radiotherapy, and
endocrine therapy must be provided in tandem because many
clinical results indicate that the combination of these modalities
can provide better survival benefit than one in isolation. HIFU
is a local therapy for noninvasive destruction of the tumor, and it
is essential to combine it with other therapies in clinical applica-
tions. However, some cancers, such as renal cell carcinoma and
pancreatic cancer, are not sensitive to chemotherapy and radio-
therapy. Similar to surgical operation, HIFU can become the
only therapeutic option offered to the patients.
There are two goals of HIFU in the treatment of patients with
solid malignancy. One goal of this ablation in patients with early
stage cancer is to achieve a cure, and HIFU should be used as
a local treatment to induce complete necrosis of the targeted
tumor. Additional treatments, such as chemotherapy, radio-
therapy, and endocrine therapy, are essential to patients with
breast cancer for conservation of the diseased breast, if HIFU is
used locally in patients with early stage breast cancer. In surgical
oncology it is necessary to resect the entire tumor along with
an adequate tumor-free margin to prevent local recurrence. In
the same way, HIFU treatment should adopt a similar principle
and aim to kill the entire malignant focus along with tumor-free
15.7 Clinical applications of
Extracorporeal US-Guided
HIFU for Solid Malignancies
Since HIFU was first used in the 1950s for patients with neu-
rological disease during surgical procedure, it has been studied
in the laboratory to treat normal tissue and implanted tumors
