Amanda Smolock (Medical College of Wisconsin, Milwaukee, USA) discusses how her practice operates, using microwave ablation nearly exclusively for primary and metastatic liver tumours targetable under ultrasound (US) and/or computed tomography (CT) guidance.
Patients are typically discussed at a multidisciplinary liver tumour conference and referred to the interventional radiology (IR) clinic for evaluation. At consultation, a full history and physical exam is completed along with updated laboratory studies, including complete blood count, liver function studies, and coagulation tests. Patients with good performance status and preserved liver function are considered appropriate for percutaneous liver ablation. Contrast-enhanced (CE) CT images or magnetic resonance images (MRI) are obtained within one month of evaluation and procedure. US assessment is performed at the clinic visit to ensure sonographic visibility and percutaneous approach for ablation. The approach is communicated with the procedure team and helps to streamline preparation on the procedure day.
Procedures are scheduled for general anaesthesia in the interventional CT suite and proper patient positioning for the procedure is a team effort: a posteriorly located tumour may require oblique positioning of the patient, and safe positioning of arms overhead improves CT image quality.
Non-contrast and multiphasic CE-CT are typically obtained prior to probe placement. This helps to review anatomy pre-procedure, confirm tumour location and size, and optimise the percutaneous approach. When possible, probes are placed under direct US guidance. Few cases have tumours visible only on CT or only after lipiodol staining with transarterial chemoembolization (TACE). In these cases, CT navigation software is used to optimise probe placement, which is often best in double oblique approaches to maximise both safety and efficacious tumour treatment. Respiratory manoeuvres in concert with the anaesthesiology team are utilised as needed to accurately and precisely target tumours with ablation probes. A non-contrast CT is obtained to confirm and document probe position. Hydrodissection and/or biopsy, if being performed, are done after securing ablation probe position(s). CT and US are complementary imaging to confirm appropriate tumour targeting and predict ablation zone coverage. Activated probes and ablation zone formation are monitored in real time with US and intermittent CT. This allows for confirmation of ablation zone formation and coverage.
Another CE-CT is obtained at the conclusion of the ablation. Total contrast volume is split between pre- and post-ablation CE-CT, not to exceed 150–200ml of iodinated contrast agent. Post-ablation CE-CT assesses ablation zone coverage of the tumour with adequate margins and also evaluates for any complications. If margins are inadequate, additional ablation can be performed at this time.
A recent addition to our practice is MR-guided cryoablation. This technology allows ablation of small liver metastases that are visible only on MRI. Patient positioning and tumour targeting require additional considerations to maintain safety in the MR environment.
Patients receive a check-up telephone call from a nurse the day after the procedure and are then seen one month post-procedure in clinic along with CE-CT/MR. Follow-up with imaging occurs every three months, which may be extended to every six months after one year of documented complete response.
Amanda Smolock is assistant professor at the Division of Vascular and Interventional Radiology, Department of Radiology, Medical College of Wisconsin (Milwaukee, USA).
Relevant disclosures: consultant/speaking faculty and grant recipient/research support, Neuwave Medical.
