Nonsurgical Cancer Treatments

Interventional radiology methods are little known in our country, but increasingly important in cancer treatment. The proportion of cancers diagnosed early rises every day, moving us away from conventional surgery. These methods are performed by specialist interventional radiologists.

Surgery has remained an indispensable main cancer treatment for almost centuries. Particularly over the past 20-30 years, major advances have occurred in technology and medical (drug) cancer treatment. Once certain cancers were found sensitive to chemotherapy and radiotherapy, surgery was abandoned for these tumors or restricted to selected patients. Nasopharyngeal cancer, cancer of the upper throat, is one example. In early and advanced laryngeal cancer, radiotherapy and chemoradiotherapy have also replaced surgery. As radiotherapy's importance increased and technology revolutionized the field, it came into use for many cancers. Modern technologies have achieved success approaching surgery in locally recurrent cancers and many cancers unsuitable for surgery. Over time, this success led stereotactic radiotherapy to be called SRS (radiosurgery) . Today, radiosurgery is highly popular for brain tumors, many recurrent cancers of limited area and size, early-stage lung cancer and prostate cancer.

Alongside radiotherapy innovations, cancer treatment methods have been developed including radiofrequency, laser, microwave, HIFU (high-frequency ultrasound waves), Nano-Knife (irreversible electrotherapy), and have begun almost replacing surgery in many cancers. Unlike damage to normal tissues in radiotherapy's treatment field, damage from these methods performed by interventional radiologists is extremely limited, and repeat applications are possible. In these methods, also known as percutaneous tumor ablation, needles are inserted through the skin into the tumor. Depending on the method, different devices connected to these needles, also called electrodes, deliver cooling gases, ultrasound waves, radiofrequency or electric currents. Tissue is thus destroyed across the entire tumor. Such methods are called minimally invasive cancer treatments . During treatment, ultrasound, MRI and tomography provide three-dimensional tumor assessment. Correct needle placement and, depending on the ablation method, the destroyed tissue area can be assessed with imaging during and after the procedure.

Percutaneous ablation first involves reviewing the patient's previous CT, ultrasound, MRI and PET-CT images. The type, number, size and location of tumors planned for ablation are evaluated. The available information then guides planning for each patient and tumor: which ablation method to use, which imaging during the procedure, where to enter through the skin and what type of anesthesia to administer.

Most ablations can be performed while the patient is awake under local anesthesia and sedation.

Ultrasound is preferred for imaging because it is convenient; tumors not visible on ultrasound are generally ablated under CT guidance.

In some situations, using both angiography and CT during ablation may help. For example, some liver tumors invisible on standard CT and ultrasound can be visualized and treated using CT after contrast delivery through a catheter placed in the hepatic artery during angiography. In recent years, angiography equipment with “Cone Beam CT” has allowed both CT and angiography with one device. These devices particularly make lung biopsies and ablations easier and safer.

Which Ablation Methods Are Used in Cancer Treatment?

Currently, 3 groups of methods are used for percutaneous cancer ablation:

1. Chemical ablation,
2. Thermal (heating/freezing) ablation,
3. Irreversible electroporation (nanoknife).

Chemical Ablation

This destroys a tumor by injecting chemicals such as alcohol or acetic acid into it. It is an effective, safe method used worldwide for more than 20 years. Its main advantages are low cost and few side effects. However, complete tumor destruction generally requires multiple, sometimes many, interventions.

It is most commonly used for liver tumors, particularly primary liver cancer (hepatocellular carcinoma). It is also used for thyroid tumors and lymph node metastases.

Thermal Ablation

This destroys a tumor by heating or freezing it with an electrode placed in its center. Heating methods are;

• radiofrequency,
• microwave,
• laser and
• ultrasoundas the methods used.

Radiofrequency ablation (RFA) is the most popular, followed by microwave. In radiofrequency, alternating electric current moves ions within tissue. Friction from this movement becomes heat and destroys tissue. Microwave uses high-frequency electromagnetic waves to move tissue water molecules, generating heat. The basic difference is that radiofrequency uses electric current and microwave uses electromagnetic waves to generate heat. Both are effective in conductive areas such as the liver and soft tissues, but experience with radiofrequency is much greater.

In relatively insulating tissues such as lung and bone, radiofrequency may not generate sufficient heat; microwave may theoretically be more effective there. Radiofrequency and microwave are most often used for liver, lung, kidney, bone and soft tissue tumors.

Another thermal ablation method is cryoablation (freezing). Special needles called probes, inserted through the skin into the tumor center, freeze and destroy tumor tissue. Cryoablation is most commonly used in the kidneys and prostate and less often in the lungs, liver and breast. Its main advantage is the sharply defined visibility of destroyed tissue on ultrasound, CT and MRI during ablation.

Irreversible (Permanent) Electroporation (Nano-Knife)

Irreversible electroporation delivers brief, very high-voltage electric current to irreversibly increase cell wall permeability and permanently destroy tumor tissue. Conventional reversible electrotherapy has been used for nearly 100 years, but its success remained poor and its use consequently declined. During the procedure, high electric current (several thousand volts) irreversibly increases cell wall permeability. In this type of electroporation, permeability does not disappear, and the cell loses viability.

Nano-Knife has been tested in pancreatic, biliary tract and prostate cancers, and its use has increased rapidly worldwide as effectiveness became apparent. However, the method's difficulty, need for general anesthesia, requirement for an experienced team and expense are its main limitations.

Today it is most often used in pancreatic and bile duct cancers and prostate cancer. At diagnosis, pancreatic cancer is usually locally advanced, meaning it has spread to major vessels around the pancreas, making surgery impossible.

Nanoknife can kill tumor tissue without damaging these vessels beside the pancreas.

It has also been shown not to damage other vessels in the area or the duodenum. However, safe Nanoknife ablation in pancreatic cancer requires 3-4 needles to be placed parallel to each other at the tumor margins without passing through vessels or intestines. Maximum use of imaging and an experienced physician are therefore very important. In recent years, surgical opening of the abdomen and nano-knife application under direct visualization of the pancreatic tumor and vascular structures have produced promising results. Very experienced teams are needed for this treatment.

Which Tumors Are Treated with Ablation?

Chemical Ablation is most frequently used for hepatocellular carcinoma , the primary liver tumor. Acetic acid and alcohol have successfully ablated this tumor for years. It is also used for thyroid nodules and some lymph node tumors. Today, chemical ablation is mainly used where thermal methods are technically difficult or risky, and sometimes combined with thermal ablation to enhance their effects.

Thermal ablation is currently the most widely used ablation technique; radiofrequency ablation in particular has become increasingly widespread worldwide for approximately 15 years. Like other ablation methods, it has been used most often in the liver. However, it is also frequently used for lung, kidney, spleen, lymph node, bone and soft tissue tumors. Its chief advantages are easy application, controlled and predictable ablation, and few side effects. The aim is to burn the tumor together with an approximately 1 cm layer of surrounding healthy tissue. Many studies have established that thermal ablation can completely kill tumor tissue in the burned area. Consequently, whereas it was previously used only in patients unsuitable for surgery, it is now considered a potential substitute for surgery in some patients, particularly with liver tumors.

Alongside these strengths, thermal ablation has certain weaknesses;

1. Because flowing blood carries away the heat generated during thermal ablation, tumor tissue around vessels may not be heated adequately. This “Heat Sink” effect protects the vessel wall from ablation but may prevent complete destruction of surrounding tumor tissue.
2. In ducts containing fluids such as bile or urine, which flow more slowly than blood, the heat sink effect is smaller, allowing surrounding tumor tissue to be readily destroyed. However, without the protective heat sink effect, thermal ablation may damage bile and urinary ducts.
3. Thermal ablation can destroy nerves as well as vessels and ducts. Applied in an organ such as the prostate, it can therefore cause urinary incontinence and impotence.
4. Thermal ablation near digestive organs such as the stomach and intestines may damage them. To prevent this, various methods must move the tumor area away from these organs during ablation.

Thus, for the reasons above, thermal ablation may not be sufficiently effective or safe for tumors close to major vessels, bile and urinary ducts, important nerves and hollow digestive organs such as the stomach and intestines.

One tumor most frequently treated with irreversible electroporation (Nano-Knife) is cancer of the pancreatic head. The pancreatic head lies very close to the hepatic artery, small intestinal artery and vein, and duodenum. Thermal ablation such as radiofrequency is therefore infrequently used for pancreatic tumors. Irreversible electroporation, however, can kill tumor tissue without damaging vessels or the small intestine in this area. Some recent studies have demonstrated its safety and effectiveness in many pancreatic cancer patients.

Another application of irreversible electroporation is liver tumors beside major vessels and bile ducts. In these tumors, radiofrequency and other thermal methods may damage bile ducts and insufficiently affect tumor tissue around major vessels. Irreversible electroporation may be more successful and safe. However, compared with thermal ablation such as radiofrequency and microwave, it is technically more difficult, takes longer, costs more and requires general anesthesia.

In conclusion, every percutaneous ablation method has its own advantages and disadvantages. Interventional radiologists with sufficient knowledge and experience should decide which method to use for which tumor.

What Are the Advantages and Disadvantages of Percutaneous Ablation?

Like surgery and high-dose radiotherapy, percutaneous ablation can treat certain cancers. Its advantages over surgery are entry through the skin under local anesthesia, no hospitalization requirement and lower risk. Its advantages over radiotherapy are effectiveness independent of tumor type and the possibility of repeated applications when needed.

For many patients, percutaneous ablation supports these methods rather than replacing them.

For example, in the same patient, some tumors may be treated surgically, others with radiotherapy and others with percutaneous ablation.

Percutaneous ablation also has disadvantages. The risk of local recurrence, a tumor returning at the same site, is slightly higher than with surgery and radiotherapy. However, the same area can be ablated again after recurrence. Other disadvantages, as with surgery, are that results depend on the operator's knowledge and experience, and the necessary equipment and personnel are available in few places.

Radiofrequency Ablation

Needles that open like an umbrella after placement in the tumor deliver alternating current to tumor tissue. This moves positively (+) and negatively (-) charged ions in cancer cells back and forth, generating an average temperature of 80-100 degrees around the needle. The heat causes tissue death in an area approximately 3-5 cm in diameter. The size of the destroyed area varies with needle type and number.

Radiofrequency ablation has been used in cancer for more than 25 years. Initially used in liver cancers and metastases, it later became widespread in lung, kidney, thyroid and bone tumors.

Cryoablation

Cryoablation destroys cancerous tissue by freezing. High-pressure Argon gas passes through needles placed inside the tumor and is released at the tip. The sudden pressure drop cools tissue to minus 40-80 degrees, producing a freezing effect. The Joule-Thompson effect is the name of this phenomenon, in which an iceball forms around the cryoablation needle. This iceball causes extensive tissue death through ice crystal formation in the tumor, vessel blockage and cellular self-destruction (apoptosis).

Needles placed in the tumor during cryoablation are called "probes" or "cryoprobes". Cryoprobes are straight needles with a narrower internal channel carrying high-pressure Argon gas, as noted above. Each needle can produce 2-3 cm of ablation, or tumor destruction. In large tumors, increasing needle numbers can enlarge and reshape the ablation area. For example, an ablation diameter of approximately 2 cm with a single needle, when 4 needles are used, reaches 5 cm, allowing large tumors to be treated. Today's cryoablation devices can connect 25 cryoprobes simultaneously, and percutaneous ablation can also be performed in very large tumors.

The most popular use of cryoablation is in early-stage prostate cancer and kidney cancers. However, considering advantages and disadvantages, it can also be used for tumors in various organs and soft tissues, including lung cancer and metastases.

Microwave Ablation

Microwave ablation developed in parallel with the microwave heaters used in our kitchens. Waves generated through needles (antennas) make tissue water molecules oscillate, and their friction produces temperatures of 80-100 degrees in tumor tissue. The heat kills cancerous tissue within an approximately 3cm-diameter area around the needle. This area may increase or decrease somewhat with ablation duration and needle type and number. Microwave ablation delivers electromagnetic waves rather than electricity to tissue.

The needles used in this method, introduced into medicine after the 2000s, are called antennas. It can be used for liver cancers, lung metastases and soft tissue tumors.