The Future of Microwave Ablation of Primary and Metastatic Liver Cancer | Varian

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The Future of Microwave Ablation of Primary and Metastatic Liver Cancer

The Future of Microwave Ablation of Primary and Metastatic Liver Cancer

The role of microwave ablation (MWA) for the treatment of hepatocellular carcinoma and metastatic liver cancer has broadened based on positive clinical studies demonstrating its effectiveness and safety compared to other thermal ablation technologies.1-3

At Varian, we have noted these developments with great interest, as we are dedicated to improving outcomes for cancer patients and committed to developing new technologies to support physicians towards achieving this goal. We maintain that, through the development of new microwave ablation technologies and imaging solutions that provide continuous feedback, enable improved predictability, and enhance clinical decision making, we can empower physicians to rapidly adopt and incorporate these technologies into clinical practice.

While considered standard of care for unresectable liver tumors,4 the use of MWA is evolving as a more minimally invasive alternative to surgery for some patients. With this expanded role for MWA in the treatment of primary and metastatic liver cancers, there is a concurrent need for the development of next-generation MWA technologies that enable physicians to perform the procedure more easily and predictably.

To obtain insights into the challenges associated with the use of current MWA technologies and potential options for improving procedural outcomes in patients with liver cancer, Varian recently interviewed two key opinion leaders in the field of interventional oncology: Andrew J. Gunn, M.D., Associate Professor, Division of Interventional Radiology at the University of Alabama Birmingham (UAB) and Medical Director of the Interventional Radiology and Interventional Radiology Residency Programs at UAB, and William Rilling, M.D., Professor of Radiology and Surgery and Vice-chair of Clinical Affairs at the Medical College of Wisconsin.

Dr. Andrew J. Gunn. and Dr. William Rilling.

Dr. Andrew J. Gunn. (left) and Dr. William Rilling (right)

What is one of the biggest challenges you face with the use of the current technologies for MWA?

Dr. Gunn: With larger tumors more than one probe is needed and the result is overlapping ablation zones, which creates more complexity. It is important to be able to plan in advance the best positioning for the probes and to have the confidence that the burn will go as planned.

Dr. Rilling: Knowing what you are going to get each time with ablation technology is important. I see inconsistencies in the ablation zones from one patient to another despite consistent power and time parameters. Being able to predict and plan what you are going to need from a time, temperature, and power perspective as well as the number of probes needed, without relying on ex-vivo data would be helpful. Currently there is no way to set patient specific parameters, for example, if the patient has a fatty liver, and being alerted if runaway ablation is beginning to occur. There is a need to have a more accurate ‘real time’ understanding of what the ablation zone is and to be able to adapt this intraprocedurally.

What do you see is the value of having planning and confirmation software?

Dr. Gunn: Ablation confirmation software is important to most physicians using MWA technologies for liver cancer. Having the ability to monitor temperature in the ablation zone and near critical structures would enable greater effectiveness and better safety of the technology. For example, it would be great if the system could alert you if the temperature was rising above a preset level near the colon.

While having the ability to plan the needle path and set the desired margin pre-operatively is important, it would be valuable to be better able to ensure the needle path is not different from what was planned. Having a technology which more predictably provides a needle path that aligns with the planned approach would be beneficial.

Dr. Rilling: My eyes have been opened with the margin confirmation software. I was not using this prior to the ACCLAIM trial (ID NCT05265169). I feel you need to have this level of rigor for every procedure. Everyone thinks they are visual spatial experts and can do it in their heads, but being able to have an analysis of the registration of the tumor and where you are in order to assess risk and how much ablation to apply improves the ability to do a clear margin (A0) ablation.

For newer technologies, it would be ideal to have the ability to have continuous registration during the procedure to ensure you are where you think you are. Once you start ablating, the initial targets disappear, and this means you need to really ensure the initial targeting is accurate. I recently had a case where it looked like the probes were where they needed to be based on the pre-op CT, but the ablation zone was more caudal than we wanted. Even though it looked perfect, it was actually off by quite a bit. We discovered this discrepancy when we performed margin confirmation, and the zone was not where we thought it was. As a result, we had to do another overlap. This is a bigger problem when you are trying to treat smaller tumors and where extremely accurate targeting is important.

What can be done to increase the ability to incorporate new MWA technologies into clinical practice by more interventionalists?

Dr. Gunn: Currently, repeatability depends on the physician getting used to the probes and the technology. If physicians have not done a lot of procedures with the technology, then they may not be fully confident in what the technology will deliver. Having MWA technology that produces a more predictable ablation and delivers what is expected will ease the way towards adoption of newer technologies and eliminate the reliance on past personal experience with previous generations or versions of the technology.

Dr. Rilling: It is important that we work towards having MWA technology that ‘democratizes’ the procedure so that it is not so complicated or esoteric that only 5% of interventionalists can get the best outcomes. It needs to be the other way around. We need technologies that ensure a physician who does a relatively low volume of ablations a year also has good outcomes. We also need to change the culture and set a new standard for liver tumor ablation. The ACCLAIM trial will help with this. If someone is doing liver tumor ablation, they should be doing margin confirmation in some way, shape or form, 100 percent of the time, to ensure good clinical outcomes. Newer technologies will make it better for physicians not doing it every day to achieve this.

Varian is pleased to be among the industry partners supporting the “Ablation with Confirmation of Colorectal Liver Metastases” (ACCLAIM) multicenter prospective trial designed to establish MWA as the preferred curative therapy for selected colorectal liver metastases that can be ablated with sufficient margins.


  1. Han Y, Zhao W, Wu M, Qian Y. Efficacy and safety of single- and multiple-antenna microwave ablation for the treatment of hepatocellular carcinoma and liver metastases: A systematic review and network meta-analysis. Medicine (Baltimore). 2022 Dec 23;101(51):e32304. doi: 10.1097/MD.0000000000032304. PMID: 36595779; PMCID: PMC9794220.
  2. Dou Z, Lu F, Ren L, Song X, Li B, Li X. Efficacy and safety of microwave ablation and radiofrequency ablation in the treatment of hepatocellular carcinoma: A systematic review and meta-analysis. Medicine (Baltimore). 2022 Jul 29;101(30):e29321. doi: 10.1097/MD.0000000000029321. PMID: 35905207; PMCID: PMC9333547.
  3. Tang Y, Zhong H, Wang Y, Wu J, Zheng J. Efficacy of microwave ablation versus radiofrequency ablation in the treatment of colorectal liver metastases: A systematic review and meta-analysis. Clin Res Hepatol Gastroenterol. 2023 Aug;47(7):102182. doi: 10.1016/j.clinre.2023.102182. Epub 2023 Jul 20. PMID: 37479137.
  4. Benson AB, D'Angelica MI, Abbott DE, et al. Hepatobiliary Cancers, Version 2.2021, NCCN Clinical Practice Guidelines in Oncology. J Natl Compr Canc Netw. 2021;19(5):541-565. Published 2021 May 1. doi:10.6004/jnccn.2021.0022