Microwave ablation in a hepatic porcine model: correlation of CT and histopathologic findings

International multicentre prospective study on microwave ablation of liver tumours: preliminary results

BACKGROUND

Microwave ablation (MWA) is increasingly utilized in the treatment of hepatic tumours. Promising single-centre reports have demonstrated its safety and efficacy, but this modality has not been studied in a prospective, multicentre study.

METHODS

Eighteen international centres recorded operative and perioperative data for patients undergoing MWA for tumours of any origin in a voluntary Internet-based database. All patients underwent operative MWA using a 2.45-GHz generator with a 5-mm antenna.

RESULTS

Of the 140 patients, 114 (81.4%) were treated with MWA alone and 26 (18.6%) were treated with MWA combined with resection. Multiple tumours were treated with MWA in 40.0% of patients. A total of 299 tumours were treated in these 140 patients. The median size of ablated lesions was 2.5 cm (range: 0.5-9.5 cm). Tumours were treated with a median of one application (range: 1-6 applications) for a median of 4 min (range: 0.5-30.0 min). A power setting of 100 W was used in 78.9% of cases. Major morbidity was 8.3% and in-hospital mortality was 1.9%.

CONCLUSIONS

These multi-institution data demonstrate rapid ablation time and low morbidity and mortality rates in patients undergoing operative MWA with a high rate of multiple ablations and concomitant hepatic resection. Longterm follow-up will be required to determine the efficacy of MWA relative to other forms of ablative therapy.

Microwave tumor ablation: mechanism of action, clinical results, and devices

Microwave ablation uses dielectric hysteresis to produce direct volume heating of tissue. Microwaves are capable of propagating through many tissue types, even those with high impedance such as lung or bone, with less susceptibility to "heat-sink" effects along vessels. Microwaves are highly conducive to the use of multiple applicators, showing the synergy seen with other energies, but also the potential capability for phasing of the electromagnetic field. As a result, larger, more customizable ablation zones may be created in less time. Although multiple microwave ablation systems are currently available, further study and continued development are needed.

Interstitial microwave transition from hyperthermia to ablation: historical perspectives and current trends in thermal therapy

This work reviews the transition from hyperthermia to ablation for cancer treatment with interstitial microwave (MW) antennas. Early work utilising MW energy for thermal treatment of cancer tissue began in the late 1970s using single antennas applied interstitially or the use of multiple interstitial antennas driven with the same phase and equal power at 915 or 2450 MHz. The original antenna designs utilised monopole or dipole configurations. Early work in thermal therapy in the hyperthermia field eventually led to utilisation of these antennas and methods for MW ablation of tumours. Efforts to boost the radiated MW power levels while decreasing antenna shaft temperatures led to incorporation of internally cooled antennas for ablation. To address larger tumours, MW treatment utilised arrays that were simultaneously activated by either non-synchronous or synchronous phase operation, benefiting both hyperthermia and ablation strategies. Numerical modelling was used to provide treatment planning guidance for hyperthermia treatments and is expected to provide a similar benefit for ablation therapy. Although this is primarily a review paper, some new data are included. These new data show that three antennas with 2.5 cm spacing at 45 W/channel and 10 min resulted in a volume of 89.8 cm(3) when operated synchronously, but only 53.4 cm(3) non-synchronously. Efficiency was 1.1 (synchronous) versus 0.7 (non-synchronous). MW systems, treatment planning, and image guidance continue to evolve to provide better tools and options for clinicians and patients in order to provide better approach and targeting optimisation with the goal of improved treatment for the patient.

Results of single-probe microwave ablation of metastatic liver cancer

AIMS

Microwave ablation (MWA) is the most recent development in the field of local ablative therapies. The aim of this study was to evaluate the variability and reproducibility of single-probe MWA vs. radiofrequency ablation (RFA) of liver metastases smaller than 3cm in patients without underlying liver disease.

METHODS

Sixteen liver metastases were treated using MWA, and matched for size and localisation with 13 metastases treated by RFA. Tumour diameters and postoperative ablation diameters were recorded (D1 transverse; D2 antero-posterior; D3 cranio-caudal; mm) on computed tomography scans.

RESULTS

Median D1, D2, and D3 ablation diameters after MWA vs. RFA were 18.5 (12-64) vs. 34 (16-41)mm (p=0.003), 26 (14-60) vs. 35 (28-40)mm (p=0.046), and 20 (10-73) vs. 32 (20-45)mm (p=0.025), respectively. As compared to RFA, the variability between the lesions after MWA was significantly higher for D2 (p<0.0001) and D3 (p=0.002) but not for D1 (p=0.15). The ablation diameters were less uniform after MWA than after RFA (p<0.001).

CONCLUSION

Ablation diameters after single-probe MWA of metastatic liver tumours are highly variable and suboptimal. Improvements are needed before MWA can be implemented routinely.

Thermal ablation for unresectable liver tumours, time to move forward?

Even with the advent of laparoscopic techniques for liver tumours, classic resections still represent a major undertaking for numerous liver lesions. The avoidance of surgery using ablative techniques has been the aim for over 20 years. Large volumes can now be rapidly treated with low morbidity with the many technical developments and modifications of the delivery probes. Despite these advances recurrences rates remain high with all of the presently available techniques. The biological and pathophysiological basis underlying may help explain their limitations and are important in understanding where they may be appropriately applied and ways in which they may be improved in the future.