Microwave ablation
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Microwave ablation is a form of thermal ablation used in
interventional radiology Interventional radiology (IR) is a medical specialty that performs various minimally-invasive procedures using medical imaging guidance, such as x-ray fluoroscopy, computed tomography, magnetic resonance imaging, or ultrasound. IR performs bo ...
to treat
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
. MWA uses
electromagnetic waves In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) lig ...
in the microwave energy spectrum (300 MHz to 300 GHz) to produce tissue-heating effects. The oscillation of polar molecules produces frictional heating, ultimately generating
tissue necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
within solid tumors. It is generally used for the treatment and/or
palliation Palliative care (derived from the Latin root , or 'to cloak') is an interdisciplinary medical caregiving approach aimed at optimizing quality of life and mitigating suffering among people with serious, complex, and often terminal illnesses. Wit ...
of solid tumors in patients who are nonsurgical candidate.


Medical uses

For isolated, nonmetastatic
lung tumors Lung tumors are neoplastic lung nodules. These include: Primary tumors of the lung/pulmonary system: * Bronchial leiomyoma, a rare, benign tumor * Lung cancer, the term commonly used to refer to ''carcinoma of the lung'' * Pulmonary carcinoi ...
, surgical resection remains the reference standard for treatment. However, many patients are precluded from surgery due to poor cardiopulmonary function, advanced age, or extensive disease burden. For these patients, minimally invasive therapeutic options such as
radiofrequency ablation Radiofrequency ablation (RFA), also called fulguration, is a medical procedure in which part of the electrical conduction system of the heart, tumor or other dysfunctional tissue is ablated using the heat generated from medium frequency alternat ...
, microwave ablation, and
cryoablation Cryoablation is a process that uses extreme cold to destroy tissue. Cryoablation is performed using hollow needles (cryoprobes) through which cooled, thermally conductive, fluids are circulated. Cryoprobes are positioned adjacent to the target in ...
have emerged as possible alternatives. Tumor ablation of thoracic malignancies should be considered a viable treatment option for patients with early stage, primary or secondary lung cancers who are not surgical candidates or for patients in whom
palliation Palliative care (derived from the Latin root , or 'to cloak') is an interdisciplinary medical caregiving approach aimed at optimizing quality of life and mitigating suffering among people with serious, complex, and often terminal illnesses. Wit ...
of tumor related symptoms is the intent. MWA is regarded as a particularly efficient option for the treatment of lung tumors since unlike RFA it does not rely on impedance to generate heat, rather electromagnetic microwave waves heat matter by agitating water molecules in the surrounding tissue, producing friction and heat. Another common use for microwave ablation is the treatment of
liver tumors Liver tumors (also known as hepatic tumors) are abnormal growth of liver cells on or in the liver. Several distinct types of tumors can develop in the liver because the liver is made up of various cell types. Liver tumors can be classified as beni ...
. For nonsurgical patients, local thermal ablation techniques have enabled local control of tumors without resection. In particular, this therapy has grown in use for patients with
hepatocellular carcinoma Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer in adults and is currently the most common cause of death in people with cirrhosis. HCC is the third leading cause of cancer-related deaths worldwide. It occurs in t ...
, since many patients present with advanced disease or compromised liver function. Clinical applications of MWA have also included treatment of renal, adrenal, and bone malignancies. The goals of ablation of thoracic malignancies include: 1. Ablating the entire tumor and a margin of normal parenchyma surrounding it 2. Avoiding injury to critical structures 3. Creating a large ablation area quickly.


Adverse effects

The most common adverse effects of MWA for lung tumors include pain, fever,
pneumothorax A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve ...
, and
pleural effusions A pleural effusion is accumulation of excessive fluid in the pleural space, the potential space that surrounds each lung. Under normal conditions, pleural fluid is secreted by the parietal pleural capillaries at a rate of 0.6 millilitre per kil ...
. -12/sup> Rib fractures, following thermal ablation, particularly MWA, have been newly noted in the literature. 3/sup> One of the limitations of thermal-based ablation therapies, including MWA, is the risk of marginal recurrences and/or residual disease. Residual or recurrent tumor is particularly likely in areas adjacent to heat sinks, such as larger blood vessels or airways. Theoretically, the greater heat intensity generated in MWA compared to other thermal modalities should allow for more complete ablations in larger tumors and thus decreased incidence of residual disease or recurrence at the tumor margins. /sup>


Procedure

MWA allows for flexible treatment approaches, including
percutaneous {{More citations needed, date=January 2021 In surgery, a percutaneous procedurei.e. Granger et al., 2012 is any medical procedure or method where access to inner organs or other tissue is done via needle-puncture of the skin, rather than by using ...
,
laparoscopic Laparoscopy () is an operation performed in the abdomen or pelvis using small incisions (usually 0.5–1.5 cm) with the aid of a camera. The laparoscope aids diagnosis or therapeutic interventions with a few small cuts in the abdomen.Medli ...
, and open surgical access. Therapy is generally performed with the patient under
conscious sedation Procedural sedation and analgesia (PSA) is a technique in which a sedating/dissociative medication is given, usually along with an analgesic medication, in order to perform non-surgical procedures on a patient. The overall goal is to induce a decr ...
; however, in cases where intra-procedural pain is problematic a
general anesthetic General anaesthetics (or anesthetics, see spelling differences) are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include an induced coma ...
may be used. Ablations can be performed using a single MW antenna or a cluster of three to achieve a greater ablation volume. /sup> Tumor temperatures during ablation can be measured with a separate thermal couple; tumors are treated to over 60 °C to achieve coagulation necrosis.


Platforms

Currently, there are six MWA systems commercially available in the United States. The systems use either a 915 MHz generator (Evident, Covidien, Mansfield, MA; MicrothermX, BSD Medical, Salt Lake City, UT; Avecure, Medwaves, San Diego, CA) or a 2450 MHz generator (Certus 140, Neuwave, Madison, WI; Amica, Hospital Service, Rome, Italy; Acculis MTA, AngioDynamics, Latham, NY). The MW antennas used are straight applicators with active tips ranging in lengths from 0.6 to 4.0 cm. Five of the six available systems require that the antennas are internally cooled with either room-temperature fluid or carbon dioxide to reduce conductive heating and to prevent possible skin damage. /sup>


History

The technique for thermal ablation in the lung by using
radiofrequency ablation Radiofrequency ablation (RFA), also called fulguration, is a medical procedure in which part of the electrical conduction system of the heart, tumor or other dysfunctional tissue is ablated using the heat generated from medium frequency alternat ...
was first described in 1995 for use in animal lung tumor models and then in 2000 in humans. -2/sup> Microwave ablation has emerged as a newer ablation modality and an addition to the arsenal of minimally invasive cancer care. The purported benefits of microwave ablation over other heat-based modalities such as radiofrequency ablation and laser include a larger and faster volume of tissue heating with a given application. Unlike radiofrequency ablation, MWA does not rely on an electrical circuit allowing for multiple applicators to be used simultaneously. /sup>


References

# Goldberg SN, Gazelle GS, Compton CC, McLoud TC (1995). Radiofrequency Tissue Ablation in the Rabbit Lung: Efficacy and Complications. Acad Radiol 2(9). # Dupuy DE, Zagoria RJ, Akerley W, Mayo-Smith WW, Kavanagh PV, Safran H (2000). Percutaneous radiofrequency ablation of malignancies in the lung.
AJR Am J Roentgenol The American Journal of Roentgenology (''AJR'') is a monthly Peer review, peer-reviewed Scientific journal, journal that covers topics in radiology. It is published by the American Roentgen Ray Society (ARRS) and is based in Leesburg, Virginia, Le ...
174(1). # Dupuy DE (2009). Microwave Ablation Compared with Radiofrequency Ablation in Lung Tissue – Is Microwave Not Just for Popcorn Anymore? Radiology 251(3). # McTaggart RA, Dupuy DE (2007). Thermal Ablation of Lung Tumors. Tech Vasc Interv Radiol 10(2). # Dupuy DE (2011). Image-guided Thermal Ablation of Lung Malignancies. Radiology 260. # Lencioni RR, Crocetti L, Cioni R, et al. (2008). Response to Radiofrequency Ablation of Pulmonary Tumours: A Prospective, Intention-to-treat, Multicentre Clinical Trial (the RAPTURE study). Lancet Oncol 9(7). # Simon CJ, Dupuy DE, DiPetrillo TA, et al. (2007). Pulmonary Radiofrequency Ablation: Long-term Safety and Efficacy in 153 Patients. Radiology 243(1). # Kang S, Luo R, Liao W, Wu H, Zhang X, Meng Y (2004). Single Group Study to Evaluate the Feasibility and Complications of Radiofrequency Ablation and Usefulness of Post Treatment Position Emission Tomography in Lung Tumours. World J Surg Oncol 2(30). # de Baère T, Palussière J, Aupérin A, et al. (2006). Midterm Local Efficacy and Survival after Radiofrequency Ablation of Lung Tumors with Minimum Follow-up of 1 Year: Prospective Evaluation. Radiology 240(2). # Dupuy DE, DiPetrillo T, Gandhi S, et al. (2006). Radiofrequency Ablation Followed by Conventional Radiotherapy for Medically Inoperable Stage I Non-small Cell Lung Cancer. Chest 129(3). # Wolf FJ, Grand DJ, Machan JT, Dipetrillo TA, Mayo-Smith WW, Dupuy DE (2008). Microwave Ablation of Lung Malignancies: Effectiveness, CT Findings, and Safety in 50 Patients. Radiology 247(3). # Feng W, Liu W, Li C, et al. (2002). Percutaneous Microwave Coagulation Therapy for Lung Cancer. Zhonghua Zhong Liu Za Zhi 24(4). # Alexander ES, Hankins CA, Machan JT, Healey TT, Dupuy DE (2013). Rib Fractures after Percutaneous Radiofrequency and Microwave Ablation of Lung Tumors: Incidence and Relevance. Radiology 266(3 Interventional radiology