As an interventional radiologist at Stanford, Gloria Hwang, MD, uses a variety of ablation techniques to kill small tumors in her patients — radiofrequency ablation, cryoablation and microwave ablation. But recent advances in microwave systems have improved Hwang's ability to destroy larger tumors, up to four centimeters in size, and tumors embedded in blood rich organs like the liver, giving patients whose diseases were once inoperable a chance to become tumor free.
"Microwave ablation offers an option for a significant number of people who may feel like they've run out of options," says Hwang. "That's a lot of what we do in interventional radiology — treat the sickest patients who can't tolerate toxic medications or major surgery."
Larger zone of kill
Both microwave ablation and radio frequency ablation (RFA) kill tumor cells by heating up the tissue around needles placed through the skin. But RFA heats tissue relatively slowly, so nearby blood vessels can have a cooling effect on the ablation zone.
"With microwave ablation, you can heat tumors up very quickly, using higher heat than RFA, and you can do so near blood vessels because you can stop the cooling effect of the blood vessels," says Hwang. Microwave ablation also allows interventional radiologists to use multiple probes at the same time, and delivers a relatively spherical ablation zone. "All of this together means you can get larger zones of kill and treat bigger tumors with microwave ablation," she says.
There's also a fundamental difference in how microwaves heat the tissue, Hwang says. Rather than passing an electrical current through the patient's body, as radiofrequency ablation does, microwaves heat the tissue by oscillating nearby water molecules. Microwaves do not require patients to wear grounding pads, and microwave energy can pass through air, which means it can be used to treat tumors in organs such as the lung.
"The ability to treat tumors in the lung is one of the biggest reasons physicians have become interested in microwaves," says Paul Laeseke, MD, PHD, a radiology resident at Stanford, and clinical affairs director at NeuWave Medical, the developer of the microwave ablation system used at Stanford. "Lung cancer is so common. And many people with lung cancer have a number of co-morbidities, so they're not very good candidates for surgery." Microwave ablation gives this population of patients a new opportunity to become tumor free.
The minimally invasive procedure is performed as a single treatment session, doesn't require a lengthy hospital stay, quickly treats tumors that are otherwise difficult to eradicate and does so with minimal damage to healthy tissue.
When to consider microwave ablation
Microwave ablation is most commonly used in the liver, lungs, kidneys and bone. According to Hwang, patients should be referred to an interventional radiologist at Stanford if they have liver-dominant metastatic disease with good control of the primary site; masses ideally four centimeters or smaller in size; three or fewer masses; and patients with peripheral lung tumors (primary or metastatic) who are not good candidates for surgery.