Aim
Lung cancer deaths in the industrialized world are equaling the deaths of colorectal, breast and prostate cancer combined. For treatment of early-stage non-small cell lung cancer (NSCLC) surgical resection remains gold standard. Where surgery is not possible, stereotactic ablative body radiotherapy (SABR) is recommended. Microwave ablation (MWA), whilst equally efficacious for local control, MWA is often overlooked as a valid treatment option.
This retrospective observational study is assessing characteristics of histologically proven malignant lung lesions post MWA. Examination of positron emission tomography (PET) avidity and distinct morphological features of the ablated lesion was evaluated to ascertain whether conclusive statements of the overall treatment outcome (completely or partially treated vs local recurrence/ progression) can be drawn.
Method
57 Patients post MWA therapy were assessed. These patients had their pre and post ablation computed tomography (CT) scans evaluated for distinguishable morphological characteristics. CT and PET at least 6 months post treatment and up to most recent imaging was used to evaluate lesion characteristics and avidity to establish if there was evidence of local recurrence, local regional progression and or distant metastasis.
Results
The typical morphological characteristics of lung nodules 24 hours (baseline scan) post MWA was the presence of circumferential ‘ground-glass opacification’ presenting a halo-like appearance around the ablated target lesion, thus significantly increasing the ‘lesion’ size. Over time the target lesion continuously shrunk, a minority however decreasing to or below the initial size. Necrosis, cavitation and occasional late calcification was seen. Avidity and size were not shown to be an accurate measure of treatment outcome.
Conclusion
Whilst CT morphology and PET avidity are useful in assessing treatment success, the final decision – especially if relevant for further treatment option – is to be made individually, backed up by repeat tissue diagnosis if necessary.