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Page 2 of 10 Zhao et al. Mini-invasive Surg 2018;2:26 I http://dx.doi.org/10.20517/2574-1225.2018.27

INTRODUCTION
CT-guided thermal ablation has developed in the last 20 years as a minimally invasive management option
[1]
for pulmonary malignancies, both primary and secondary, in patients who are non-surgical candidates .
Radiofrequency ablation (RFA), an electric current-based heating technique, has been the most evaluated
[2]
method . Microwave ablation (MWA), which uses an electromagnetic field around the ablation device
to create heat, is a more updated technique with theoretical advantages in terms of lesser susceptibility to
[2,3]
heat-sink effect, larger ablations, more uniform ablation zones, and shorter procedural times . Ablation
failure and subsequent local tumour progression remain an issue for both methods, with tumour diameter
greater than 3 cm, proximity to a large vessel and insufficient ablative margin being risk factors for fail-
[2,4]
ure . There are limited data on the role of repeat ablation for local progression of lung tumours after prior
[5-7]
ablation, and with most data on repeat RFA . This retrospective cross-sectional study aimed to evaluate
the safety and efficacy of repeat MWA and RFA, in locally progressing lung tumours after prior ablation(s)
at a large tertiary hospital.

METHODS
Patients
Ethics approval for this study was obtained from the Hospital Institutional Review Board (HREC/14/
QRBW/553). Patients were identified using the radiology thermal ablation database at our large tertiary
hospital. Data were collected retrospectively through systematic review of patient charts and imaging.
Inclusion criteria were consecutive patients who underwent repeat percutaneous CT-guided thermal abla-
tion of a lung tumour for local progression after prior ablation(s) between December 2009 and March 2017.
There were no exclusion criteria for this study. Repeat ablation was defined as the most recent ablation
procedure, after prior ablation(s). All lesions were referred for ablation if patients are medically inoperable
or refuse surgery. Patients were informed of the risks and benefits of ablation, and all provided written in-
formed consent for the procedure.

Ablation procedure and imaging follow-up
Ablations were performed percutaneously under CT guidance (Philips Brilliance 64, Eindhoven, The
Netherlands, replaced in 2015 by Aquilion ONE, Toshiba Medical Systems, Otawara, Tochigi, Japan). Both
RFA and MWA modalities were used (with MWA having replaced RFA at our institution by mid-2010). All
ablations were performed by the same interventional radiologist who had more than 15 years’ experience
in image-guided ablation. No prophylactic antibiotic treatment was administered. The ablation applicator
was inserted under sterile conditions under CT guidance, with analgesia and sedation administered by the
anaesthetic team. Parameters such as the type of applicator, number of overlapping ablations, ablation du-
ration, and amount of energy delivered were based on individual tumour size, location and tumour charac-
teristics. Patients received a chest X-ray 3 h post-procedure to assess for post-procedural complications, and
in all MWA cases, a limited non-contrast CT scan of the ablated site was performed 24 h post-procedure.
Technically successful ablation was defined as completed planned ablation cycle(s) and circumferential
perilesional ground-glass opacity. Patients were requested to have serial repeat CT scanning at 3, 6 and
12 months post-ablation and 6 monthly scans thereafter to evaluate treatment outcome. An FDG-PET scan
was also requested at 6 months post-ablation.

Outcomes
Safety of the procedure was assessed by presence or absence of adverse events. Adverse events were record-
[8]
ed and classified in accordance with the Common Terminology Criteria for Adverse Events version 4.03 .
Efficacy of the procedure was assessed by local tumour response to ablation and survival time. For MWA,
the limited CT scan of the ablated site 24 h post-ablation served as the baseline scan that all subsequent fol-
low-up scans were compared against; for RFA, the immediate post-ablation scan was used. Local progres-