MR-Guided Laser Ablates Liver and Kidney Tumors

Pilot Study Yields Successful Results: An Expert Interview With Eric Walser, MD

Steven Fox

April 20, 2011

April 20, 2011 (Grapevine, Texas) — Editor's note: A small pilot study has shown success using a magnetic resonance (MR)–guided laser technique to ablate small tumors in the liver and kidney. The study was presented here at the American Society for Laser Medicine and Surgery (ASLMS) 31st Annual Conference.

Eric Walser, MD, an interventional radiologist at the Mayo Clinic in Jacksonville, Florida, presented the study, and afterward he talked with Medscape Medical News regarding the technique.

Dr. Eric Walser

Medscape: This was a pilot study detailing your results using an MR-guided laser technique to treat liver and kidney tumors. Can you give us background on the development of the procedure and how it works?

Dr. Walser: Early attempts at ablating tumors with laser occurred in Europe, where doctors successfully destroyed liver tumors using various techniques. Although effective, early laser ablation had some drawbacks, including the requirement for a large insertion device and the inability to monitor the volume of tissue destruction.

We are using a newer generation of laser ablation equipment (Visualase, Inc) that utilizes a small laser fiber introducer, as well as computer software that interfaces directly with the MR machine and allows us to precisely determine the amount of tissue destruction as it is occurring. So this newer device gives us a great deal of control over tumor destruction, using a fairly small and very flexible introducer.

When we're treating a tumor in the liver or kidney, the special needle and applicator are inserted through the skin directly into the tumor, using the MR machine to guide placement of the needle.

When the laser fibers are in place, the anesthesiologist holds the patient's breath for about 90 seconds, and the laser is activated, destroying the tumor. The computer screen displays a special color-coded image of the organ and the tumor, so that we can see precisely the margins of the tumor destruction.

Laser ablation works by a irradiating a small volume of tissue using laser energy with a wavelength of about 980 nm. Solid organ tissue strongly absorbs this wavelength, causing intense heating. Above 50° to 60° Celsius, tumor cells will die. Sometimes in larger tumors we have to place 2 to 4 laser fibers to completely ablate the tumor.

After ablation, the laser applicators are removed, leaving only small puncture wounds covered with Band-Aids.

Medscape: Please tell us about your study — your patient cohort, the basic design, and the findings.

Dr. Walser: While these laser devices have been used to ablate tumors in the brain, there is limited experience in other organs. This study describes our early experience with laser ablation of tumors within the kidney and the liver.

We have now treated about 15 patients with liver or kidney tumors (7 liver lesions and 8 renal lesions). All patients underwent laser ablation with 1 to 4 laser fibers, using real-time MR temperature monitoring.

After the ablation procedure, patients had follow-up imaging 3 to 4 months later, with clinical follow-up as well.

We found the patients tolerated the laser ablation procedure quite well. Most were kept overnight for pain control and observation, but no patients had significant issues with pain or bleeding. One patient developed a pneumothorax caused by transpleural needle placement during treatment of a liver tumor. This pneumothorax resolved spontaneously. Two patients required repeat ablation due to some residual tumor, so that was a retreatment rate of about 13%.

Medscape: What are the primary advantages of this treatment over existing therapies?

Dr. Walser: Laser ablation is good for some types of tumors, but not so good for others. We have found laser ablation is excellent for small tumors in the liver or kidney that can't be seen using [computed tomography] scan or ultrasound scanning.

Secondly, because an MR scanner can image a patient in any direction or plane, this gives us great flexibility in placing the laser fibers into tumors, especially in places difficult to access, such as high in the liver, or at the top of the left kidney near the spleen.

Thirdly, laser ablation is quite useful in cases where the tumor is close to a very delicate structure, such as a bile duct or the colon, or a sensitive blood vessel or nerve. That's because laser energy can be very tightly controlled.

Other methods of thermal ablation (such as those using radiofrequency or microwave energy) create a more gradual zone of ablation, where the border between dead and living tissue is difficult to predict.

Finally, laser energy destroys tumor cells quickly — 1 to 2 minutes compared to the 10 minutes required for other types of thermal ablation. This time factor may not seem important, but it quickly adds up when you are treating a larger tumor or multiple small tumors, using several ablations in a row.

One disadvantage of laser ablation is the relatively small volume of tumor ablated by each fiber (an olive shape about 2 cm in diameter). Therefore, when we treat large tumors in areas not surrounded by heat-sensitive organs, nerves, or blood vessels, we usually use other methods.

Medscape: What about complications of this approach? Did you encounter any significant problems?

Dr. Walser: We had no serious complications with laser tumor ablation. Despite ablating tumors in fairly difficult and sensitive places, no collateral damage occurred in any of our patients. The most serious complication was the self-limited pneumothorax that I described previously. The most common problems patients had were those related to general anesthesia, such as nausea and grogginess for a few hours after the procedure.

Additionally, after thermal tumor ablation, it is fairly common to experience some low-grade fevers and fatigue for about a week. This is due to the body's resorption of dead tissue. Patients report the feeling to be similar to a mild case of flu.

Medscape: Do patients who undergo the procedure require any special follow-up?

Dr. Walser: We maintain contact with the patients to make sure that their postprocedural pain is well-controlled. Some patients take oral pain medicine for 3 to 5 days after the procedure.

It's important to follow these patients using [computed tomography] or MRI about 3 to 4 months after the ablation. You don't want to do this imaging any sooner than that, because you may see a lot of enhancement of the tumor and the surrounding tissues, due to the inflammation that's always seen after thermal ablation. This is normal, but can be confusing, since inflammation and tumors have a similar appearance.

We wait 3 months to get a better idea of the adequacy of our treatment.

Medscape: What are your recommendations to clinicians, based on your experience so far with this procedure?

Dr. Walser: I would suggest clinicians consider laser ablation of tumors when they are small (<3 cm), especially if they are near sensitive tissues or are only visible by MRI.

Dr. Walser has disclosed no relevant financial relationships.

American Society for Laser Medicine and Surgery (ASLMS) 31st Annual Conference: Abstract 182. Presented April 3, 2011.

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