Thermal Ablation Therapy and Other Ablative Therapies
Ablation treatment is an emerging treatment option for cancer patients. Ablation uses extreme temperatures to destroy tumors or alleviate blockages and other symptoms. It is a minimally invasive procedure that has become common since the advent of modern imaging in the 1990s. Ablative therapies include radiofrequency (RF) ablation, microwave ablation and cryotherapy.
Thermal ablation therapy procedures involve a thin, needle-like probe that is inserted through the skin into the tumor. The probe must be able to reach and access the tumor directly, therefore doctors use ultrasound, CAT scans or an MRI to guide the probe into the tumor. Once in place, the probe emits various energy sources through the tip such as RF electrical current, microwaves, laser light and ultrasonic waves until temperatures rise to cytotoxic levels (50-60 °C). This will heat and kill the tumor. Of these various energy sources, RF and microwave ablation are most commonly used worldwide for the last 20 years.
During RF ablation, alternating electrical current (~500 kHz) produces resistive heating around the interstitial electrode. Skin surface electrodes (ground pads) are used to complete the electrical circuit. Studies suggest it may be the first-line treatment option for small hepatocellular carcinoma (liver cancer) and renal-cell carcinoma (kidney cancer).
Even though RF heating produces good results, it is hampered by local blood flow and high electrical impedance tissues such as lung, bone, desiccated or charred tissue. Microwaves may lessen some of these problems by producing faster, volumetric heating. To create larger or conformal ablations, multiple microwave antennas can be used simultaneously while RF electrodes require sequential operation, which limits their efficiency. Studies found that early experiences with microwave systems suggest efficacy and safety like, or better than RF devices.
Non-thermal procedures such as cryoablation can freeze cancerous tumors. This is a result of cold gases including liquid nitrogen or argon flowing through a probe to form a ball of ice crystals at its tip to surround and freeze the mass. NanoKnife® is another type of ablation which uses electrical current instead of heat or cold to destroy tumors. Ablation therapy may be a treatment option for patients who have tumors that are three centimeters or smaller, this includes kidney tumors and tumors in the lungs, liver, and bones as well as soft-tissue tumors of the breast, adrenal glands, and head and neck.
Ablation therapy is often chosen when other therapies would be harmful or not be beneficial to the patient. For example, the liver is the site of cancers that originate from both liver cells and from tumors arising from distant sites, such as the colon. The most effective treatment of tumors originating in or spreading to the liver is surgery. Unfortunately, many patients are not candidates for surgery because of the number or location of the disease, or because their health does not permit extensive surgery; therefore, ablation therapy for liver cancer is appropriate for patients with four or fewer small tumors limited to that organ. Ablation of the liver may not be the best choice for patients with a greater number of tumors, or tumors involving multiple organs, and instead chemotherapy and other forms of therapy are recommended. This is also true for lung cancer. RF ablation is the technique most commonly used when lung cancer ablation is the chosen therapy to treat tumors in the lung.
Some of the benefits of ablation therapy, whether it is thermal or non-thermal, may include:
- Can be performed without open surgery.
- It has a reduced cost.
- Can be used to treat tumors when surgery is not an option.
- Can relieve pain and blockages.
- Requires a shorter hospital stay and recovery time.
- Can be used with other cancer treatments.
- If new tumors develop, it can be repeated.
- Requires a shorter hospitalization stay.
- Can increase preservation of surrounding tissues.