High-intensity focused ultrasound treatment for thyroid nodules

Introduction
High-intensity focused ultrasound (HIFU) is a thermal ablation technique that uses focused ultrasound energy to cause necrosis in the underlying dermal tissue. The thyroid is located close to the epidermis and subcutaneous layers, making it an organ suitable for this procedure. Data shows that HIFU ablation can effectively shrink benign nodules and alleviate nodule-related symptoms, offering a good alternative for patients unwilling or unsuitable for traditional thyroid surgery. Therefore, one of the primary patient groups for this procedure is those with benign thyroid nodules causing symptoms who wish to avoid traditional surgical removal.
This new surgical procedure leaves no scars on the neck and does not require general anaesthetic, being a minimally invasive surgery. Patients can generally be safely discharged on the same day of the operation, with no need for an overnight hospital stay.

Surgical procedure
The patient lies supine with the neck slightly extended, and anaesthesia is induced with a single dose of diazepam (10 mg) and pethidine (50 mg).Occasionally, the area around the target nodule is anaesthetised with 10 mL of lidocaine 1%. The surgical equipment comprises an energy generator, a [transducer], a skin cooler and a touchscreen for planning.The instrument’s [transducer] comprises an [image transducer] (7.5 MHz, 128 elements, linear array) and a HIFU transducer (3 MHz, single element, 60 mm diameter).The [transducer] is manoeuvred into position under ultrasound guidance so that the treatment area covers the entire target nodule. Once the nodule has been locked onto the device’s screen, the device’s computer(Beamotion version no. TUS 3.2.2, Theraclion, Paris, France) automatically divides the nodule into multiple ablation units (volumetric pixels). Each volumetric pixel is approximately 7.3 mm thick and 5 mm wide.The device delivers a continuous 8-second pulse of HIFU energy to each volumetric pixel, followed by a 20–30-second cooling period, before moving on to the next adjacent volumetric pixel. This cycle is repeated until all volumetric pixels within the treatment plan have been processed.Before the procedure begins, organs in the vicinity of the treatment area—such as the carotid artery, trachea and skin—are highlighted on the device’s screen to ensure safety.To prevent accidental burns to nearby vital organs, the device automatically defines safety margins based on the following parameters and excludes any volumetric pixels within these margins: (a) within 0.5 cm of the skin;(b) within 0.5 cm of the trachea and recurrent laryngeal nerve; and (c) within 0.2 cm of the ipsilateral carotid artery.Furthermore, the device is equipped with a laser motion detector which will cut off the power supply should it detect the patient moving or swallowing during the procedure.To prevent skin burns, the tip of the instrument’s [probe] is fitted with a small ball (containing a liquid maintained at 10°C) to cool the skin.The initial energy for the ablation procedure is 280 joules per pulse, subsequently increasing to 360 joules per pulse until a [high-echo signal] appears at the focal point.The device automatically records data such as the total energy (kilojoules) delivered to the nodule, the [acoustic beam] energy (sonication) and the time required (minutes).

Programmatic risk
There's a possibility that a HIFU procedure could lead to the following issues:

1. Burns, bruises, redness and oedema of the skin at the treatment site (<1%).
2. The area being treated or where pain or discomfort is felt (<5%).
3. Hoarseness or difficulty speaking caused by partial paralysis of the vocal cords usually lasts for several months (<2–3%).
4. Chronic pain, such as that caused by nerve damage or loss of sensation, leaves burn marks on the skin during the process (<1%).
5. Incomplete nodule reduction (defined as a reduction of less than 50% over 6 months), and regrowth of the nodule many years after the ablation procedure (with a probability of up to 15%).
6. [Horner’s Syndrome] (1%).

Patients may also experience the following discomforts due to the medication used in the ablation procedure:
Dizziness, vomiting, headaches, indigestion (heartburn or stomach ache), and changes in blood pressure or heart rhythm (blood pressure too high or too low, or slow heart rate).

Pre-operative preparation
Patients should fast for 6 hours before surgery, and may start fasting from 12:00 the night before until the end of the operation. Only patients with thyroid nodules need to fast. Patients do not need to stop taking any medication.

Post-operative care
No special care is required after surgery. Most patients can resume a normal diet immediately after treatment. Patients are usually given an ice pack to relieve swelling in the neck.

Follow-up appointment
Patients requiring follow-up at the Endocrine Surgery Clinic (Block S, 4/F, Queen Mary Hospital) after surgery to monitor nodule shrinkage and undergo thyroid examination as needed.

Notes
This leaflet is for reference only and does not list all possible complications. Other unforeseen complications may occur. The actual risks may differ for certain categories of patients. Please contact your doctor for more information.

Source: https://www.ekg.org.hk/pilic/public/surgery_pilic/surgery_HIFUforthetreatmentofthyroidnodules_0310_chi.pdf