2 May 2003 17:00 GMT

by Joe Mc Cool

Alternatives to current X-ray mammography techniques are being proposed involving the use of microwaves - waves similar to the radio frequency emitted by mobile phones.

X-ray mammography is the leading method of breast cancer detection and treatment, but it is dangerous, sometimes painful, and unsuitable for young women or women with dense breast tissue. There is also a risk of false positive and false negative diagnoses.

Tumors have significantly different electrical properties to normal, healthy tissue. The passage of microwaves through breast tissue, for instance, varies according to disease state.

Elise C. Fear from the University of Calgary, Canada has been focussing on turning this observation to clinical use. She claims that the approach she has devised promises to be safe and low-cost, involving microwave powers only half those required by a mobile phone.

Her main problem is that even in the absence of tumors, breast tissue is not entirely uniform, consisting of contrasting fat and glandular material. Also, microwaves are inclined to bounce off the skin and distort the images. So there are a lot of challenges still to be overcome.

Fear believes, however, that this wide property range in breast tissue "may also provide a basis for assessing and possibly diagnosing benign and pre-cancerous conditions."

The work of her team is still at the detection stage and centered on computer models and phantoms (tissue-mimicking materials), the team has not yet tried to treat any patients.

"I'd like to see our system move to the clinic - but this may take a few years of further research," said Fear. However, she adds, the system is being tested at Dartmouth College in New Hampshire, US, but only on selected subjects. "The researchers are still assessing the technology when applied to patients rather than phantoms," she said.

A more therapeutic approach, this time applied to skin cancer, is being taken by Paul Stauffer and his team at the University of California. He has designed what he terms a "microwave vest". This takes the form of a flexible printed circuit board that can wrap round an affected part of the patient's body.

Small, concentric flat spiral antennae featured on the vest act as both transmitters of radio frequency and receivers. Hence, he can both heat cancerous areas beneath the skin for long periods and help monitor the temperature there. Heat applied like this acts as an adjuvant, he says, aiding the effectiveness of other treatments such as chemotherapy.

Several vests have been built and used in his clinic to heat patients with superficial cancers. "These are prototypes," admitted Stauffer, "but I have just received another research grant from the NIH to continue development and refinement of my current heating system."

Research has shown that tumors exist at a slightly higher temperature than that of surrounding tissue, and it is hoped that this characteristic can be exploited. Stauffer's approach can be used to detect areas of higher temperature.

While recognizing the work of Professor Fear, Stauffer suggests that one of his applications "could lead to a somewhat simpler system for locating small regions of elevated temperature (tumors) in otherwise slightly cooler breast tissue - using a multi-antenna conformal array that fits the breast snugly and reads temperature as a function of depth under each of the radiometric receiver[s]."

Stauffer says that the primary difference between his and Fear's approaches, "is that I am searching for small regions of higher temperature, while Dr Fear is attempting to provide a system to provide a complete image of electrical or temperature distributions in breast." He suggests that his simpler configuration would not require as high a spatial or temperature resolution as Fear's technique.

However, both researchers predict that their techniques will be used alongside regular X-ray mammograms for some time to come. Stauffer predicts, nevertheless, that the approach "should hopefully significantly lower the false postive and false negative diagnoses that plague standard mammographic examinations."