New for November 2011!
The origins of this page date back to 2007 (thanks to Daniel) and
more recently thanks to Eamon McErlean of Emblation Limited. Thanks!
here to go to a daughter page on VSWR problems encountered in
The Varian boys out of Stanford
(Microwave Hall of
Famers!) pretty much made Medical Linear Accelerators the mainstay
of cancer treatment with their research in the 1940's, eclipsing
the use of active Cobalt 60 radiation sources with a much more controllable
and "power-off" safe radiation source. From the early
1970's to today the Medical LINAC (portmanteau
for linear particle accelerator) has been the work horse of the
medical cancer treatment industry.
Just yesterday (euphemistically
speaking) we had Thyratrons, triggering Klystrons, modulating outputs
of electron guns, with outputs running down waveguides, through
bunching and steering coils, pulling 270 degree turns with bending
magnets to precisely "nail" a target to output a selection
of as many as six different electron energies and maybe 4 photon
energies from anywhere in a 360 degree rotation. Yes, with a waveguide
Today (literally) Computed Tomography
(radiological CT) and Linear Accelerator technology have been married
together into a single system with a common source to deliver the
most precisely controlled radiation dose that has ever been delivered.
In addition to radiation, another
important use of microwave energy in medicine is for the thermal
ablation of tissue. In this application microwave energy is used
to create localised dielectric heating (diathermy) resulting in
controlled destruction of tissue. Microwave
ablation (MW ablation) is the next evolution of diathermy treatment
and being a radiating technology overcomes many issues such as current
conduction problems with grounding pads as used in high frequency
and radio frequency diathermy.
Watch a video
on RF ablation of varicose veins
Compare RF and MW ablations
simultaneously using an ex-vivo window model,
filmed by the Tumor Ablation Lab at the University of Wisconsin
Microwave ablation also provides
desiccation of tissue without the excessive charring and nerve damage
associated with RF ablation. Various applications include treatment
of large tumours or removal of unwanted tissue masses, for example
liver tumours, lung tumours and prostate ablation. Microwaves can
also be used to coagulate bleeding in highly vascular organs such
as the liver and spleen.
As microwaves have shorter wavelengths
the choice of frequency can benefit the application, for example
large volume ablations can typically be made at 915 MHz and 2.45
GHz and use of higher frequencies in the range 5.8 GHz - 10 GHz
can create shallow penetration of energy resulting in very precise
ablations suitable for treatments such as skin cancer, ablation
of the heart to treat arrhythmia, uterine fibroids, multiple small
liver metastases, corneal ablation (vision correction), spinal nerve
ablation (back pain), varicose vein treatment, verrucae treatment
and many other specific treatments.
A few common misconceptions about
microwave ablation include the use of frequencies chosen to align
with ISM frequency bands. The IEC standard 60601-2-6 "Particular
requirements for the safety of microwave therapy equipment"
is applicable to treatments operating from 300 MHz but not exceeding
30 GHz. Typically ablation treatments are intended not to radiate
into air and therefore shouldn't create interference with non-ISM
Another common preconception
about using microwaves in surgery is that they are uncontrollable.
This has arisen as a result of using standard industrial magnetrons
and basing measurements such as reflected power in microwave medical
equipment on ideal 50 ohm microwave components. Modern microwave
generators may employ stable reliable solid state sources however
the dielectric properties of tissue varies considerably during treatments
therefore microwave applicators (antennas)
are not always optimally matched to an ideal 50 ohms which can result
in significant mismatch. This can result in measurement uncertainty
and VSWR problems which accounts for the perception of an uncontrollable
treatment. Recent techniques, such as those developed by Emblation
Limited, overcome this problem in medical microwave applications
to create a mismatch tolerant controllable user experience that
enhances patient safety and treatment reliability for the next generation
of microwave ablation treatments.
Leading research in the use of
microwave in medicine is being carried out at University of Wisconsin,
Dartmouth College, Duke University, University of Bath, Bangor University
and at many other leading universities. The technology has successfully
been commercialised into treatments offered by a number of companies
including Covidien, BSD medical, H.S. Hospital Service, Neuwave
and an ever increasing number of other organisations.
In the field of oncology MW ablation
now offers a new tool in the arsenal of weapons to fight cancer,
providing new opportunities to save many lives.