According to recent research from Reto Bale and colleagues, multi-probe stereotactic radiofrequency ablation with intraprocedural image fusion represents an efficient invasive therapy for hepatocellular carcinoma (HCC), as confirmed by histopathologic examination in explanted human livers. Therefore, it may be an attractive candidate for the initial treatment option even in patients with tumours larger than 3cm. Here, Bale speaks to Interventional News about the importance of this work, and advocates for the inclusion of image fusion into guidelines outlining standard of care.
What are the advantages of stereotactic radiofrequency ablation (SRFA) over standard radiofrequency ablation (RFA)?
For successful ablation, it is crucial to ablate the complete lesion, including a sufficient safety margin of at least 0.5cm. The short axis of the ablation zone with one RFA or microwave ablation (MWA) probe is limited to 1.5–4cm, depending on the ablation technology and probe design. Thus, even with the latest generation of MWA probes, only lesions up to a maximum diameter of 3cm can be effectively ablated with one single probe position. Therefore, for lesions larger than 3cm, overlapping ablation zones are required. This task is very difficult if only conventional US- and CT- [ultrasound and computed tomography] guidance is used for probe placement.
Stereotaxy allows for precise 3D planning of multiple probe positions, and then for precise probe placement intraprocedurally according to the plan. In addition, integrated image fusion allows for immediate and precise evaluation of probe placement and of the result during the intervention. Due to the ability to plan and introduce multiple needles with high precision, very large tumours can be completely devitalised. The largest mixed hepatocellular carcinoma (HCC)–intrahepatic cholangiocellular carcinoma (ICC) treated by our group (in 2014) had a diameter of 18cm. In a recent control CT four years after the initial SRFA, the lesion is still local recurrence free.
What are the clinical ramifications of this research?
In international guidelines, resection is recommended as a first line treatment in HCC larger than 2–3cm. If these large lesions are not resectable, a combination therapy of thermal ablation and transarterial chemoembolization (TACE) is proposed.
This work clearly shows that even large hepatocellular carcinomas can be completely devitalised (A0 in analogy to R0) by thermal ablation only. Therefore, SRFA challenges resection as first-line treatment not only in small lesions, but also in lesions greater than 3cm. Moreover, the combination therapy (thermal ablation and TACE) can be replaced by SRFA only, with excellent results, as confirmed by histopathologic examination.
Furthermore, the question arises whether liver transplantation can be replaced or at least postponed in patients with normal liver function by the application of SRFA and follow-up imaging.
What are the challenges presented by HCC treatment, and more specifically with ablative treatments?
Most HCCs develop in patients with liver cirrhosis, which is associated with impaired liver function. This has to considered if large ablations are performed. The remaining liver volume after local treatment has to be larger than in patients with a healthy liver tissue. In addition, many patients have a high portal vein pressure and an impaired coagulation function, which increases the risk of bleeding.
Why is it important to be able to treat larger tumours?
Due to its minimal invasiveness, SRFA has the potential to replace resection even in large lesions where an A0 ablation can be achieved. In my opinion, more than 90% of resections in primary and secondary liver tumours may be replaced by sophisticated thermal ablation procedures, even in large and very large lesions.
Why do patients drop out of the liver transplant waiting list? How will this potentially change?
Tumour progression beyond conventional transplant criteria during the waiting period for transplantation may result in patient dropout rate from the waiting list. Major risk factors include initial tumour load and waiting time. Using sophisticated and effective thermal ablation methods, patients may remain on a waiting list for an extended time.
What is the future of image fusion and SRFA?
Image fusion is key for immediate treatment evaluation and should be mandatory for every ablation procedure. It should be used in combination with standard CT- or US- guidance. Future guidelines should include image fusion as a standard of care and should propose stereotactic and other sophisticated planning and guidance techniques. As we stated in the paper, we strongly believe that our results justify specialised training in stereotactic techniques as well as additional costs related to infrastructure. Other centres should adapt stereotactic planning, image guidance, and image fusion in order to improve the outcome of ablation techniques even in large tumours.
Reto Bale is an associate professor of Radiology in the Department of Radiology at the Medical University Innsbruck in Innsbruck, Austria.