Laser ablation plus MR thermometry boosts survival rate for cancer patients

Colorectal cancer patients are known to survive longer if their liver metastases are removed. New research shows one method for killing cancer cells -- laser ablation guided by MR thermometry -- is safe and effective and leads to a better survival than other methods.

If liver metastases from colorectal cancer cannot be removed surgically, other options include laser ablation, cyrotherapy, and radiofrequency ablation. RFA, which most radiologists use, has a high recurrence rate, however. Laser ablation with thermometry, which basically means using MR to control for temperature, is a good alternative to other methods, according to researchers from Germany.

MR thermometry capitalizes on the fact that increasing heat reduces the T1 relaxation time and results in a decrease of signal intensity. If the treated lesion is blackened completely, therapy is finished. The temperature is above 60° C, and vital tissue is destroyed. The lesion is monitored every minute, and therapy can last between 15 and 25 minutes.

Typically during laser ablation surgery, radiologists apply laser applications under CT guidance (CT fluoroscopy) and then transfer the patient to the MR unit for laser therapy with temperature monitoring, according to lead author Dr. Ralf Puls of the department of diagnostic radiology and neuroradiology at Ernst Moritz Arndt University in Greifswald.

"Recently, we introduced a new miniaturized MR-compatible applicator. With this new applicator, the whole procedure can be performed in the MR unit, which saves time and is more acceptable for the patient," he said.

Between 1998 and 2005, Puls and his team found 87 patients with a total of 180 liver metastases from colorectal carcinoma to undergo laser ablation with MR thermometry (J Vasc Interv Radiol 2009;20:225-234). Mean follow-up was 43.5 months.

Puls and colleagues ablated 178 of the 180 metastases. Follow-up after 24 and 48 hours showed 85.6% effectiveness for eradicating metastatic tissue. After six months, the local tumor progression rate was 10%. For all treated patients, the average survival time was 50.6 months. Survival rates after the first year were 95.7%, with rates of 86.2% at two years, 72.4% at three years, 50.1% at four years, and 33.4% at five years.

Major complications were seen in 8% of all patients, a finding partially explained by the need to repeat the ablation procedure for some patients. However, the 30-day mortality rate was zero.

The improved survival but slightly higher complication rate, which included large pleural effusion, may be attributable to MR temperature monitoring, which allows exact and individually adjusted dosing of heat application for adequate ablation of metastases, the authors said.

The complication and five-year survival rates are equal to or better in comparison with other studies performing thermal ablation, including RFA studies, Puls said.

MR thermometry is universally the first choice among interventionists to monitor the progress of laser ablation, according to Pul. Technical limitations inhibit its use during RFA because radiowaves from the RF pulse interfere with the magnetic field.

This paper will affect clinical developments, but it is not a new technique, according to Dr. T.J. Vogl, director of diagnostic and interventional radiology at the University Hospital of Frankfurt.

Survival is better than with RF ablation, which means it is useful, he said.

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