Microwaves in medical therapyWorldwide, there are over ten million new incidences of cancer and more than six million deaths from cancer, annually. Despite an ever-increasing focus on addressing the disease, cancer mortality rates have not changed dramatically between 1950 and 2002. In the next ten years, cancer will cause the death of over 84 million people, worldwide.

In liver cancer, there are over 600,000 new incidences every year, across the world. Tumour resection (surgical removal) is the only treatment offering a potential cure and is normally combined with chemotherapy and other drug therapies. However, resection is often impossible due to the presence of multiple tumours, or because the patients are not fit enough for such invasive procedures. In liver cancer, only around 20% of patients are suitable for a tumour resection.

Menorrhgia solution

In 1994, research work was started on a system for the treatment of a gynaecological condition called menorrhgia. This is a painful condition which causes dysfunctional uterine bleeding and affects around 20% of women in their thirties and forties. The traditional medical solution has been hysterectomy. This is an undesirable and expensive procedure, and a less invasive and safer procedure was required. Prof Nigel Cronin at the University of Bath and Mr. Nick Sharp at the Royal United Hospital in Bath collaborated on research to develop a minimally invasive microwave-based treatment. This device operated at a frequency of 9.2 GHz - a frequency specifically tailored to treat only the endometrium, and leave the rest of the uterus unaffected.

The resulting treatment is fast and effective. The uterus is left intact, treatment only takes three minutes and it can be performed in an outpatients setting. There are benefits to the patient because a typical hysterectomy would involve a three to five-day hospital stay followed by a recovery period of anything up to two months. There are also major psychological advantages to not removing the uterus, and massive cost savings to the NHS.

Microsulis Medical Ltd was set up to commercially develop and market the system, which is called Microwave Endometrial Ablation (MEA). The system is now the market leader in this area, in the UK. MEA has a worldwide presence - with over 400 systems operating in the UK, US, Canada and many other countries. Over 75,000 successful treatments have been completed to date. MEA carries the European CE mark and United States FDA 510(k) approval.

Liver tumours

In 1998, work was started on a system for the treatment of tumours in the liver. The main collaborator in this project with the University of Bath was Mr David Lloyd, Consultant Hepatobiliary and Laparoscopic Surgeon at Leicester Royal Infirmary and Microsulis Medical Ltd. This system they developed operates at a frequency of 2.45 GHz - the same as a domestic microwave oven - and this was chosen to be optimal in the deposition of large energy doses for the treatment of large tumours. There are many systems on the market for the treatment of soft tissue tumours, but all have significant limitations and none are capable of treating 5 cm diameter tumours from a single placement location. The main design criterion of this microwave device and the principal clinician ‘user need’ was to be capable of fully treating a 5 cm liver tumour in time scales of a few minutes.

Microwave Tissue Ablation

The device for open surgical use which was developed and marketed by Microsulis Medical Ltd under the trade name of MTA™ - Microwave Tissue Ablation. MTA burns a 5cm sphere of tissue in just five minutes – three to ten times faster than radio frequency-based systems, and gives surgeons the option to treat previously inoperable patients. MTA is now used in approximately 60 centres around the world. To differentiate the oncology products from the previous gynaecological products, the brand Acculis was created.

The reaction of surgeons to the MTA system is invariably enthusiastic in the extreme, and nearly 700 treatments having been completed. The MTA system carries the European CE mark and United States FDA 510(k) approval.

Smaller devices

While the MTA device was being marketed, research continued into smaller devices suitable for radiological deployment due to a growing need from the interventional radiology arena for very small devices which could be placed directly through the skin under imaging guidance.

There are real design and engineering challenges involved in the transmission of high microwave powers down small diameter transmission lines, and the most significant of these is cable heating. The smaller the microwave cables, the more transmission losses are generated. To keep the same, highly effective power of the MTA™ device in a smaller format, it is necessary to cool the shaft of the applicator which goes through the skin and the microwave feed cables for the generator. Failure to adequately cool the applicator shaft would result in patient skin burns, and, of course, any such device would not be approved by the certifying authorities.

Percutaneous Microwave Tissue Ablation

The final 1.8 mm diameter device, under the name Accu2i™, is again marketed by Microsulis Medical Ltd, under the system name Percutaneous (through the skin) - Microwave Tissue Ablation (pMTA™) The system employs a patented cooling system with its own bespoke sterile pump unit. Operating under four bars of pressure, the pMTA system cools the whole of the applicator shaft, plus the associated feed cables, and keeps the whole device at ambient temperature.

The pMTA system is designed to be backwardly compatible with both the Accu5i and Accu20s applicators, and can be used to drive either. The microwave cable attachment connector automatically detects which applicator is being attached, and configures the machine software accordingly. At the time of writing, the pMTA system carries the European CE mark, and it is expected that FDA 510(k) approval will be received in the next two weeks. pMTA is only recently released and is already in use at over 30 surgical and radiological centres.