Physician: Prof Laura Crocetti

Location: University of Pisa - Italy

Featured product: TATO Thermal Ablation Treatments for Oncology

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During the past 20 years, the objectives of ablation research endpoints have been to increase ablation volumes while reducing the procedural times and increasing the reproducibility. This means higher wattage, cooling optimization and larger calibre antennas. Large volumes of coagulative necrosis, however, are not the only achievement that matters in daily clinical practice. While ablation can be considered a minimally invasive treatment, some risks exist and the principle of beneficence against the principle of non-maleficence should be evaluated in order to optimize the treatment, balancing safety and efficacy. By planning an ablation treatment, it is fundamental to take into consideration the presence of factors affecting treatment safety or efficacy.

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Among the potential complications affecting safety, bleeding is the most important to be prevented. Unlike surgeons, Interventional Radiologists do not have direct control of haemostasis. For this reason, ablation is considered as a high bleeding-risk procedure^[1].

When abnormalities in the coagulation are present, the risk of the occurrence of perihepatic free fluid after intervention or complications of any kind during follow-up is increased^[2]. The availability of thinner antennas may be useful in patients at risk, such as those with cirrhosis, abnormal platelets, or elevated values of INR.

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Nodules in subcapsular location treated with a direct puncture are at higher risk of bleeding and seeding. The latter especially if the nodule is not well differentiated or presents an invasive tumoral pattern^[3]. Therefore, in the treatment of subcapsular nodules, direct puncture should be avoided.

In the impossibility of interposing healthy parenchyma, “no touch” technique has been demonstrated as feasible and useful^[4]. Multi-antenna microwave devices can be useful in nodules with subcapsular location and every time the physician prefers a no-touch technique.

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Undesirable thermal damage can also affect safety and a “controlled ablation”, not growing too fast and too much in length is desirable. Structures that can be damaged are represented by:

• Muscles. Pain may follow ablation for several days or weeks.
• Main biliary tree. It is possible to perform the cooling of main biliary ducts, even if this procedure is not easy and practical^[5]
• Surrounding viscera, such as the colon or the gallbladder. In such locations, it is advisable to use artificial ascites Dextrose 5% for Radiofrequency (RF) or 0,9% NaCl for Microwave (MW)[6] but it is not always effective. When MW ablation is performed, significant tissue retraction can occur. The use of high power can sometimes induce an important tissue retraction, attracting the viscera near the ablation area even if it has not been classified as a structure at risk at the beginning of the treatment.

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In all those situations, a “controlled ablation” is desirable. While RF ablation is a mild, more controlled, and slowly growing technique, controlled MW ablation should be preferred due to its physical properties. Microwave tissue heating relies on the interaction of an electromagnetic field with water molecules in the tissue, while radiofrequency tissue heating is produced by an electric current going through the needles and the patient^[7]. RF heating is limited in areas of low electrical conductivity (where there are no ions to be flipped), such as in the lung or in the bone. On the contrary, MW are capable of propagating more effectively, heating tissues with low electrical conductivity, (high impedance) or low thermal conductivity. Unlike RF, MW heating expands beyond charred or desiccated tissues^[8]. MW are also less sensitive to the phenomenon of heat sink effect, that consists in the presence of flowing blood causing a cooling effect, thereby reducing the ablation volume^[9].

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Pneumothorax is the most frequent complication of ablation of primary and secondary lung tumors^[10]. It has been demonstrated, in lung biopsy series, that the rate of pneumothorax is related to the calibre of the needle used to puncture the lung^[11]. Due to the ability of MW to propagate effectively and heat tissues with low electrical conductivity, high impedance or low thermal conductivity such as the lung, the combination of thin antennae and MW energy delivery could provide better results in lung ablation^[12] (Picture 5).

This is especially true in case of small lung nodules such as metastases, which are often difficult to puncture as they might move” in lung parenchyma when touched by the antenna (Picture 6). The antenna can be placed on the side of the nodule and MW energy can effectively propagate and ablate the nodule and the tissue.

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Ablation of benign thyroid nodules or recurrencies of malignant thyroid neoplasms requires the availability of thin and short devices, and the possibility to carefully monitor the treatment^[13]. These treatments are usually performed under ultrasound (US) guidance: devices with optimal echogenicity and a slow-growing controlled treatment induced hyper echogenicity are mandatory for a safe treatment. MW could overcome limitations of RF in treating highly vascularized benign or malignant nodules, due to its physical properties^[14].

• 18G x 8 cm length TATO antenna is specifically designed for thyroid ablation. It is highly visible under US and the thermal induced hyper echogenicity grows slowly and in a controlled way

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Currently there are many ablation devices with inherent differences. It is important to know these differences, in order to match the patient/nodule with the correct ablation technique and to balance power and control. TATO may offer advantages in combining MW energy delivered in a controlled fashion and less invasive approach.

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