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Bale et al. Hepatoma Res 2023;9:44 https://dx.doi.org/10.20517/2394-5079.2023.71 Page 7 of 13

accounts for incomplete ablations. After thermal ablation of hepatocellular carcinoma (HCC), a minimal
[53]
ablative margin (MAM) of at least 5 mm should be attained to prevent local tumor growth . For colorectal
[54]
liver metastases (CRLM), a safety margin of at least 1 cm has been proposed . A single ablation probe
position can ablate only a limited volume, regardless of the specific ablation technology. Percutaneous
thermal segmentectomy, which combines balloon-occluded single probe MWA and then balloon-occluded
[55]
TACE, seems to be a promising approach for the treatment of large tumors (> 2-3 cm) . Alternately, ideal
coverage of the tumor including a MAM must be achieved by overlapping ablation zones. To achieve
reliable results, careful three-dimensional placement planning and a method for precise execution of the
planning are required. Conventional US- or CT-guided punctures might not be able to meet this
requirement.

Stereotactic thermal ablation
Neurosurgeons have utilized stereotaxy for years to extract tumors and conduct biopsies. It employs a 3D
coordinate system that enables precise insertion of instruments within patients [56,57] . Frame-based stereotaxy
includes screwing a frame to the patient's skull and employing computer-aided technology to calculate
instrument trajectories and distances in a Cartesian coordinate system. Invasive fixation and surgical access
restrictions limit this method . Frameless stereotactic three-dimensional navigation devices have addressed
[56]
these issues. These technologies, now standard in neurosurgery operating rooms, allow surgeons to identify
spots within the patient using a real-time 3D coordinate CT or MR system . Modern navigation systems
[58]
are used in many different clinical settings, including the liver. Using a Cartesian coordinate system, the
software allows for the planning of the needle trajectory. Adjusting the aiming device in accordance with the
[59]
virtual pre- or intraoperative plan enables the puncture of almost any part of the body through the skin .
Robot-assisted navigation systems have the advantage of providing semi-automatic adjustments compared
with passive navigation systems that necessitate manual aiming [60-63] .

Single-probe stereotactic MWA
Stereotactic systems have been utilized in conjunction with MWA (SMWA). Kim-Fuchs et al. used single-
probe SMWA to treat 10 patients with 5 primary and 6 recurrent iCCA lesions (mean tumor size: 2.1 cm)
and demonstrated that it is safe, with short hospital stays and a low complication rate . The reported local
[64]
recurrence rate was 27% (3/11).

Multi-needle stereotactic RFA
Three-dimensional planning and precise needle placement is facilitated by stereotactic methods that
[65]
enhance the efficacy of multi-needle RFA , which can define overlapping ablation areas . Using a multi-
[56]
needle coaxial technique, multiple lesions can be targeted in a single session. Moreover, coaxial needles
[65]
allow for tumor biopsies right before ablation. As the needles are positioned prior to the start of the
ablation , this technique facilitates the customization of the ablation site to a virtually arbitrary size .
[67]
[66]
[68]
Decreasing the distance between needles close to vessels can decrease the heat sink effect .
Outcomes after multi-needle thermal ablation with stereotactic guidance [Table 2]
Local recurrence and OS after multi-needle SRFA for different types of primary [69-71] and secondary liver
tumors [72-75] have been reported to be similar to those after surgery, even when the tumor was large and close
to major vessels . The first study published in 2011 reported outcomes after multi-needle SRFA of 18
[68]
[31]
primary iCCAs and 16 recurrent ICCAs in 11 consecutive patients. Despite a median lesion diameter of 3.0
cm (range: 0.5 to 10 cm) only three local recurrences (8%) were observed after a mean follow-up time of 35
months. Three major complications (13%) were noted and treated by the interventional radiologist. The
resulting 1-year and 3-year OS and median OS (Kaplan Meier) were 91% and 71%, and 60 months,