DECEMBER 15, 2005
VOLUME 2 NO. 21

ADVANCES in MEDICINE

Precision tool decimates liver CA

Stereotactic radiation therapy is much more than a last resort


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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