Journalist: Laura Durnford
October 22, 2002
Over the past few decades, doctors have been
heating up tumours as a method to help make cancer treatments more
effective. Now physicists are improving their ability to predict the heating
effects – with implications for other technologies such as mobile phones.
A hexagonal, grey plastic tube rests horizontally on a laboratory bench
in the Academic Medical Centre of the University of Amsterdam. The tank is
almost big enough to lie inside and, indeed, it represents a human body in
the experiments of physicist Hans Crezee: "This is the simplest model we
have," he explains. "We fill this with salty water and if we use 6 grams per
litre then we know that at the frequency we use for the heating equipment,
it will behave just like human tissue."
Like a real cancer patient receiving hyperthermia treatment, a specific
area within this tube is warmed by microwave beams which are fired from an
array of antennae positioned around the ‘body'. But in this case,
light-emitting diodes inside the tank respond to the microwaves'
electromagnetic fields by lighting up. "Because we've made the end of the
tube transparent, we can see the pattern of the actual power distribution in
the body," reveals Crezee. "The only problem is that it gives a very rough
distribution and we're really interested in what happens on a millimetre
scale." He adds, "Because we're using microwaves, a fundamental problem is
that we can't focus very well and that can result in some temperature
differences within the tumour."
Deep and difficult
Some cancers are easier to regulate than others and Hans Crezee is
currently attending to the problem of cancers of the oesophagus – the tube
through which food passes into the stomach. This is a particularly difficult
area to heat satisfactorily; firstly because it is seated deep within the
body and secondly because it's surrounded by various organs and blood
vessels which all dissipate incoming heat to different extents.
"It's mostly a very aggressive tumour which we can operate on, but we find
that around 30% of patients have a recurrence," says Crezee's colleague, Dr
Marten Hulshof, who's a radiation oncologist at the hospital. "Now we're
part of a new project where we're trying to combine external heating with
internal heating in the oesophagus itself. And we're also interested in
hyperthermia together with radiotherapy and/or chemotherapy, which is a new
area we're developing"
The 40-43 degree Celsius temperature achieved damages the DNA in cancer
cells and makes them less able to withstand the toxic effects of other
therapies, which are administered during the same period. Maintaining a
consistent level of heating throughout a tumour is important if the
treatment is going to be effective. Uneven heating can leave cool patches
where cancer cells have a better chance of survival. It can also produce
hotspots which can cause pain to the patient or even harm healthy tissue
around the tumour.
The ability to predict where such hot and cool spots are likely to occur,
with any given heating equipment or strategy, would be a very useful way of
optimising treatment and preventing discomfort to patients. One approach,
which has been developed by researchers at the University Medical Centre of
Utrecht, in the Netherlands, uses a two-pronged computer technique called
‘quasistatic zooming', as physicist Dr Jeroen van de Kamer explains: "The
problem of computer models used so far has been low spatial resolution, so
you get a rough image. But since human anatomy is highly detailed, we've
been creating a technique that can zoom in to a high resolution."
Dr van de Kamer's method employs two sets of mathematical formulae to
analyse the heating effects of microwaves in the human body. "It's like a
road map," he enthuses, "first you get
the large scale information like the highways, then within a region you can
do another step and look for where the small roads are."
So far this higher resolution analysis has revealed hotspots that weren't
visible using the larger scale computations. And Dr van de Kamer is positive
that the technique will help to optimise hyperthermia in cancer treatment.
But the computer analysis has been proving useful in assessing potential
heating effects from other technologies too.
"There is concern that the hyperthermia we do deliberately to cure
patients might also be caused by mobile phones and that brain tissue might
get heated and damaged," explains Dr van de Kamer. He was asked to apply his
new technique to assess a number of different phones and assess this
controversial idea. "You could see that for very fine structures, such a
very thin layer of fluid on the surface of brain tissue, there were things
that could be missed on the low resolution. And it could be that for the ear
and eye the high resolution is very useful if you're interested in power
distribution in the head. But the actual temperature is not much changed by