Traditionally, solid organ tumours have been treated with systemic chemotherapy, surgical resection, or local external beam radiation therapy. The recent development of percutaneous imaging-guided thermal ablation therapy has provided the opportunity for the minimally invasive treatment of selected focal tumours. The advantages when compared to surgery are low cost, reduction of morbidity and mortality, and an outpatient day-case procedure with quicker recovery period. Early clinical trials have produced promising results for RFA therapy of hepatocellular carcinoma, hepatic and cerebral metastases, renal and retroperitoneal tumours, and bony lesions, including osteoid osteoma.
Thermal ablation has the potential to destroy the entire tumour with heat by killing malignant cells in a minimally invasive fashion without damaging the adjacent structures. During percutaneous RF ablation the patient is essentially transformed into an electrical circuit with adhesive grounding pads on the thighs. An RF probe (which is essentially a needle with an insulated shaft, and either a straight tip or expanding multi-tines which simulates an umbrella) is inserted into the tumour under imaging guidance, a technique that is similar to a routine percutaneous biopsy. The alternating radiofrequency current agitates ions in the tissue surrounding the needle, creating frictional heat, which denatures intracellular proteins and the cell membranes are destroyed through melting of lipid layers when temperature exceeds 60 degrees Celsius. There are now a few different devices that are available in the market. These are essentially impedance or temperature controlled systems.
In our institution, we routinely use the impedance controlled system from Boston Scientific (MA, USA).
There are a range of Le Veen RFA array probes (multi tines needle electrode), which include the SuperSlim, standard and co-access systems. There is also a straight tip needle, Soloist single needle electrode (16.5 G), which is very useful for treating small tumours and can avoid any significant collateral damage. The typical ablation zone with the Soloist needle is slightly oval in shape and measures around 1cm (diameter) x 1.5cm (length).
For the SuperSlim RFA needle electrode (17G), this has size ranges from 2 to 3 cm and for each diameter size they also come in cannula lengths of either 15 or 25 cm. This can be used to treat lesions if one is considering using a probe guide with the US machine. Occasionally, one may find that in tough cirrhotic livers, this electrode may get bent during the passage into the tough liver parenchyma.
The standard Le Veen needle electrode (Fig. 1) comes in diameter sizes ranging from 2 cm (12 cm length), 3cm (12 cm length), 3.5cm (12 or 15 cm length), 4cm (15cm length) and 5cm (15 cm length). The needle electrodes for diameter sizes ranging from 2 to 3.5cm, 4cm and 5cm are 15G, 14 G and 13 G respectively.
The most commonly used kit in our institution is the 15G co-access sheathed needle system (Fig. 2), via which an 18G needle gun can be inserted to obtain a tissue biopsy and this can be immediately followed by insertion through the needle of a Le Veen RFA array probe. They have diameter sizes ranging from 3, 3.5 and 4cms. And all of them are 15cm in length. It is important to note that the co-access RFA electrode shaft is not insulated and therefore cannot be used without the co-access sheath as this will cause skin burn and you will also notice that no roll-off would be achieved!
During treatment, the needle can be positioned using US or CT guidance. The Le Veen RFA array probe is deployed fully from the outset and the treatment is performed with impedance-controlled current from a 200-W generator (Boston Scientific, MA, USA). Standard algorithms for impedance-regulated ablation were followed until impedance roll-off (impedance greater than 300 Ohms) is achieved (Fig. 3).
We also have some experience with other systems, the RITA system has a greater range of needles and allows a bigger zone of ablation. Therefore for large tumours greater than 5cm, one may consider using another system as the Boston Scientific system largest RFA array probe diameter is 5cm and the largest co-access system is 4cm. However, this can always be overcome by sculpturing zonal ablation with multiple ablations.
Occasionally, in treating residual disease, multi-tine probe can also encounter problems related to inability to deploy the umbrella of the needle due to dense scarred recurrent disease. In this situation, the forward deployment of the needle electrode such as the RITA system or the straight tip needle with the Soloist (Boston scientific) or Tyco system may be useful here.
To date, we have performed around thermal ablation in over 200 renal tumours and 50 liver tumours using this system. The longest follow up is 4-years for the renal tumours and there is no evidence of recurrent disease for our patients at the medium term follow up after the initial complete ablation.
The advantages of this system are that it is relatively straightforward to use, clear and concise algorithms, range of needles in particular the co-access system allows pre-treatment biopsy before ablation without creating another needle track. Certainly in the UK, the technical support for the system from the Boston Scientific staff is very good, to coordinate training for operator as well as providing necessary proctoring for the centre if required.
Acknowledgement: We are the preceptor centre for Boston Scientific which provides proctoring for other centre in the UK for RFA of liver and renal tumours.
Dr Tze wah
Consultant Interventional Radiologist
St James University Hospital
Leeds
UK
