introduction

Painful bone metastases commonly occur in advanced cancer patients. They are difficult to manage because of pain, reduction in mobility, and performance status.  Possible mechanisms that may cause pain from bone metastases include the following:

• Stimulation of nerve endings in the endosteum resulting from the release of
• chemical agents from the destroyed bone tissue such as prostaglandins,
• bradykinin, substance P, or histamine;
• Stretching of periosteum by increasing size of the tumor;
• fractures;
• tumor growth into surrounding nerves and tissues.
   

Few of these mechanisms are supported by definitive data. Stimulation of nerve endings in the endosteum by chemical agents released from the destroyed bone tissue is probably the main cause of bone pain from small metastases; as metastases enlarge, stretching of the periosteum additionally contributes to the pain.

Traditional therapies to control pain and to treat bone metastases include the following:

• Radiation therapy
• Chemotherapy
• Hormonotherapy (prostate, breast)
• Analgesics
• And recently, pamidronate (biphosphonate) has been recognized as useful in osteolytic lesions.
   

These conventional therapies with the well known drawbacks and side effects provide reasonable pain relief obtaining variable success rates.  Furthermore, radiotherapy and chemotherapy require a two to four week delay to reach efficiency.

In some cases, radiotherapy may not be an option because of radiation insensitivity of the tumor or high radiation doses previously delivered.  Furthermore, chemotherapy may not be recommended because of its toxicity.  Intolerable analgesic-related side effects may develop with increased doses.

Surgical resection is considered the only potentially curative option for secondary malignant bone tumors.  However, in secondary bone tumors few patients are surgical candidates.  Minimally invasive techniques with quick pain relief can be an alternative option to conventional treatments.

Several percutaneous procedures can be suggested:

• Alcoholization,
• Cementoplasty (vertebroplasty, acetabular cementoplasty), and
• Thermal ablation: 
• Laser photocoagulation
• Radiofrequency ablation
   

Radio-frequency (RF) ablation seems to be one of the most promising techniques consisting of thermal ablation of non-resectable tumors.  In the following we will describe the use of radiofrequency (RF) ablation in bone metastases with the most suitable indications, the results, the advantages and the limits of this technique compared to the existing percutaneous interventions.

PERCUTANEOUS TECHNIQUES

• Alcoholization:  Percutaneous alcoholization of bone metastases is well suited in patients with painful severe osteolytic bone metastases if conventional anticancer therapy is ineffective and requires high doses of analgesics to control pain, and rapid pain relief is necessary. The major contraindication is the risk of ethanol diffusion into vital structures.
• Cementoplasty: Painful spinal metastases are usually treated by an combination of vertebroplasty and radiotherapy. Vertebroplasty is an excellent palliative therapy with remarkable pain relief.  However, vertebroplasty with injection of cement can be insufficient in pain reduction of spinal lesions with large paravertebral invasion. Injection of cement (cementoplasty) in other bone metastases locations (acetabulum) is possible.  However, this technique is most suitable when both consolidation and pain management are required.
• Thermal ablation
  • Radio frequency (RF)
  • Laser photocoagulation: The use of radio-frequency ablation was first reported in 1990 for the treatment of hepatic tumors. The size of the thermal coagulation produced by a single radio-frequency ablation is larger than that created by a single laser ablation.

Bone metastasis alcoholization. Uneven distribution of the contrast and ethanol.

Spinal metastasis with paravertebral extension. Leakage of contrast along the needle tract. Risk of muscular and soft tissue necrosis.

Painful iliac crest metastasis. Alcoholization with excellent pain relief. Note the uneven distribution of ethanol and an anterior leakage.

Large necrosis of the metastasis after alcoholization. Notable pain relief 12 hours after the procedure.

Cervical spine lesion treated with percutaneous vertebroplasty.

No leakage of cement. Vertebroplasty allows  good consolidation and pain relief in this case.

Acetabular metastasis treated with percutaneous cementoplasty. The cement is injected inside the lytic lesion.

No leakage. Excellent pain relief. Cementoplasty allows consolidation and pain therapy in this case.

Ex-vivo liver with coagulation produced by a single laser fiber. The lesion measures 15 to 20 mm diameter after 10 mn and 2 W of power.

In-vivo RF ablation with 50 W and 10 mn application. The lesion measures 4 cm of diameter.