The liver is a hotspot for metastases.
It receives so much blood that a variety of cancers
from colorectal, to breast, to prostate and lung
can easily spread to the organ. And no matter
where it started, the prognosis for liver cancer patients
is rarely good.
That's why there's so much excitement
among oncologists about a new treatment called stereotactic
radiation therapy (SRT), which has shown great promise
in treating life-threatening liver cancer as
well as brain, prostate, and other cancers. SRT delivers
high doses of radiation that conform to the shape of
a tumour, giving the treatment a specificity that is
lacking with standard radiation. "The potential is that
these treatments could lead not only to local control
of the metastases, but also a cure," says Dr Laura A
Dawson, associate professor of radiation oncology at
the University of Toronto, who uses and champions SRT.
But for some reason the treatment has been slow to catch
on among Canadian physicians.
ZERO
IN ON TARGET
Until now, the treatment of choice for liver cancer
has been surgical resection, with affected regions of
the organ removed but only a small percentage
of patients are eligible. Chemotherapy can sometimes
shrink the lesions, but rarely gets rid of them completely,
and traditional radiation isn't possible because the
liver has a very low tolerance. "The problem is that
we breathe," explains Dr Allan Katz, assistant professor
of radiation oncology at the University of Rochester
Cancer Center. "The liver rests on the diaphragm and
moves as we breathe, so the risk of damaging healthy
parts of the organ with standard radiation is just too
important."
SRT was originally developed to
treat brain cancers, where pinpoint accuracy is required
to ensure healthy areas remain unaffected. But by discovering
ways to predict the movement of the liver based on a
patient's breathing patterns and developing new technologies
that can monitor this movement, SRT can now be used
on other parts of the body. "We localize the tumour
on the day of the treatment and train the patient to
hold their breath and remain immobile," says Dr Dawson.
Then, several beams are positioned to deliver high doses
of radiation that conform to the shape of the tumour.
SO
FAR, SO GOOD
To date, Dr Dawson and her colleagues have treated 68
liver cancer patients as part of an ongoing study being
conducted at Princess Margaret Hospital, where Dr Dawson
implemented the SRT program. Preliminary data from 36
patients, recently presented at the annual meeting of
the American Society of Clinical Oncology, showed the
treatment is safe, with no liver toxicity or other serious
side effects.
In a similar study, Dr Katz treat-ed
182 metastatic liver lesions in 72 patients with SRT.
"Eighty-eight percent of the lesions we treated shrunk,
disappeared or stayed the same," he says. "We're targeting
individual lesions, not the whole disease and
we're doubling the survival rate," he adds. The results
were presented at the American Society for Therapeutic
Radiology and Oncology's annual meeting in October.
Dr Katz and Dr Dawson are currently
working together on a study sponsored by the Radiation
Therapy Oncology Group. They hope to demonstrate the
safety of the treatment in a larger study group, measure
overall response rates and provide data on which to
build a randomized trial. Eligible patients are being
recruited in treatment facilities across the US and
Canada.
BEFORE
IT'S TOO LATE
The potential of SRT is particularly exciting because
it gives 'no-hoper' patients another chance. "For the
most part, when cancer metastasizes, you can't control
it," says Dr Dawson. "The success we're achieving with
SRT is unusual. It sets the foundation that cancers
with isolated metastases can be cured." What's more,
SRT is delivered in short cycles that typically last
no more than a few weeks, so it's easy to integrate
into an overall treatment plan. "It doesn't affect their
quality of life at all," adds Dr Katz, "and that's really
important."
Dr Dawson just returned from an
exchange visit to the Alberta Radiation Center (ARC)
in Calgary. This specialized SRT facility, which has
been open for a year, is the only Canadian centre that
has the capability to treat both brain and body sites
with the same machine. "We're currently treating patients
with brain lesions, spine tumours and prostate cancers,
and we're about to start on liver and small lung cancers,"
says Dr Peter Craighead, director of radiation oncology
at the University of Alberta and chair of the ARC Steering
Committee. With liver cancer being added to the program,
Dr Craighead hopes the facility will see more referrals
in the near future. "We had predicted 600 patients by
year three, but we probably won't reach half of that."
He hopes the referrals will pick up now that they're
doing new studies on liver, lung and spine tumours.
Dr Dawson is also frustrated with
the low number of patients being referred to her facility.
Doctors don't seem to be aware this treatment is available,
she says, adding there's no need to wait until a patient's
options have run out before considering SRT. "Most patients
with tumours smaller than 5cm are first treated with
chemo," she explains, "and yet these are the ones for
which SRT is the safest and most likely to help."
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