Thyroid nodule is a common condition that affects up to 60% of the population. There is an estimated 10% lifetime probability of developing a thyroid nodule. Although most thyroid nodules are benign, up to 10-15% can enlarge to cause compressive symptoms including neck pressure and discomfort, dysphagia, dyspnea, and dysphonia. The conventional treatment for these benign but problematic nodules has been thyroidectomy. Although generally a low risk operation, thyroidectomy is associated with some risk for recurrent laryngeal nerve injury, bleeding, infection, and need for thyroid hormone supplementation. Since the early 2000s, ultrasound-guided percutaneous thermal ablation has emerged as a potential alternative treatment to surgery for benign thyroid nodules. Of the myriad ablation methods, the most commonly used techniques are radiofrequency ablation (RFA) and microwave ablation (MWA). [1-3] A growing body of evidence shows that RFA is an effective treatment for benign solid thyroid nodules, toxic adenomas, and thyroid cysts resulting in overall volume reduction ranges of 40-80% at 1 year, with durable resolution of compressive and hyperthyroid symptoms. However, RFA is not without its limitations. Radiofrequency waves can be limited by the heat sink effect and tissue char leading to longer procedure times and potentially less optimal outcomes in larger, hypervascular, and/or more cystic nodules.

Microwave ablation (MWA) is another ablative technique that uses electromagnetic energy waves to cause tissue hyperthermia and coagulative necrosis. It generally causes higher ablation temperatures than RFA and is less subject to the heat sink effect, and therefore can facilitate more efficient ablation procedures. Current evidence comparing RFA versus MWA for thyroid ablation was limited and was either retrospective, non-randomized [4-9], under-powered, or with an unequal baseline. The results from these studies were also conflicting, suggesting suboptimal quality of evidence and bias due to non-standardized technique of ablation across studies. To date, there is no randomized controlled trial comparing the efficacy and safety of RFA versus MWA for the treatment of benign thyroid nodules. Given the higher ablation temperatures, freedom from heat sink effect, and no influence from impedance changes during ablation, MWA may achieve different treatment efficacy.

Inclusion Criteria:

1. Adult patients >/=18 years of age
2. Nodule maximal diameter ≥2cm and nodule volume <20ml
3. Nodule being predominantly solid (≥80% solid)
4. Confirmed benign nature of nodules, either by : two benign fine needle biopsies, with the most recent biopsy performed within 1 year of enrollment in study or one benign fine needle biopsy and low suspicion characteristics on ultrasound
5. Both functional and non-functional nodules are eligible.

Exclusion Criteria:

1. Cytologically indeterminate nodules
2. Nodules with substernal extension or posterior extension that cannot be viewed sufficiently with ultrasound
3. current pregnancy or cardiac arrhythmias; presence of pacemaker or any medical condition that renders patient unfit for thermal ablation