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results

Between January 1999 and January 2002, 68 patients with painful osteolytic bone metastases were treated by RF ablation in our department.  Nine thyroid cancer patients with metastatic bone lesions were treated by the combination of RF ablation and radioisotope therapy (Iodine 131).  All treated lesions were osteolytic, including: lung carcinoma, breast carcinoma, thyroid carcinoma, renal cell carcinoma, colorectal carcinoma, melanoma, endometrial carcinoma.

Prior to RF ablation, each patient was assessed by using a validated visual-analogue scale for pain evaluation, and the use of analgesic medicine was recorded.  A complete blood count and prothrombin time were obtained within 24 hours of the procedure.  If no previous histologic or cytologic proof of the patient’s malignancy had been obtained, a percutaneous biopsy was performed prior to treatment.

All patients underwent physical examination and a CT and MR imaging (maximum 2 weeks before the procedure) prior to treatment.  With the monopolar technique, the coagulation size with a single energy delivery is about 40 mm in diameter.  The coagulation with bipolar technique is strictly limited between the electrodes achieving a maximum of 3 to 4 cm.

The first follow-up is performed 7 to 10 days after the procedure with an MR examination to evaluate the necrosis.  The procedure is repeated if the ablation is not complete and/or there is insufficient pain relief.  Large bone metastases require multiple RF applications.  If necessary, the procedure can be repeated every week.

In one patient with femoral metastasis, the laser photocoagulation was preferred to RF ablation due to the presence of a centromedullar ostheosynthetic material.

During the first hours (12- 24 hours) after the procedure pain should be controlled by analgesics.  Fever is systematic after a large necrosis.  The septic risk is reduced by strict sterility.

Neurological complications are avoided by a precise anatomical knowledge of the treated region and precise CT guidance.  No major complications in patients treated in our department have been reported.  Careful selection of lesions, electrode placement, and use of bipolar technique are crucial to avoid inadvertent ablation of critical structures such as spinal cord, major nerves, bowel, and bladder.

In one case, along with the necrosis of the metastasis, there was also to a muscular necrosis with major pain for one week.  The use of the bipolar technique with limitation of necrosis between the electrodes is very promising in these cases.

MR imaging was performed 10 days and 6 months after the procedures.  The ablation zone appeared hypointense and non-enhancing.

 

In bone metastases, 75% of resections were incomplete.  Radio-frequency ablation of bone metastases was promising in pain management with 78% satisfactory results.

One of the major advantages of the RF ablation of bone metastases is the quick pain relief occurring within 24 to 48 hours.

The mechanism of action responsible for decreased pain at the metastatic site after RF ablation is unclear.  Several possible mechanisms responsible for decreased pain include:

  • mechanical decompression of tumor volume, decreasing stimulation of sensory nerve fibers;
  • destruction of tumor cells that produce nerve-stimulating cytokines (tumor necrosis factor, interleukins, and others), which may sensitize nerve fibers and affect pain transmission;
  • physical destruction of adjacent sensory nerve fibers involving the periosteum and cortex of bone, inhibiting pain transmission; and
  • inhibition of osteoclast activity, which may cause pain.

The best ablations were obtained in large metastases of thyroid cancer.  As a matter of fact, the treatment has been performed in two steps.  Initially, the radio frequency ablation was performed with destruction of more than 90% of the lesion followed by 131- iodine therapy to complete the ablation of residual tumor.  Complete necrosis was observed in 85% of these cases.

 

Large painful osteolytic metastasis.  The lesion was consolidated previously by osteosynthesis.  First, alcoholization was considered.  Injection of contrast medium demonstrates a venous leakage.  RF ablation was not possible because of the metallic material.

 

Laser photocoagulation was the only alternative.

 

Insertion of four 18-gauge spinal needle inside the lesion with coaxial insertion of the laser fibres.  Simultaneous laser energy delivery through the needles for 10 minutes.  Notable pain relief was obtained.

 

We used MR imaging in the evaluation of tumor before and after the RF ablation.

 

T1-weighted images with injection of gadolinium was useful in the appreciation of the necrosis.