**2.2. Laser ablation**

pathologic fracture.Pathologic fracture is inducedin around10% of bone metastasis, andis life-

The treatment of metastatic bone tumor includes the combination of modality including medication, radiation therapy, and surgery to reduce pain and prevent bone destruction. Recently, the use of bisphosphonate and denosumab was reported as an inhibition of osteolytic microenvironment factors. Radiation therapy is the most frequently used and effective method

Generally, patients need operation for the prevention of pathologic fracture, especially on the weight-bearing bones like vertebrae, pelvis, and femur as well as long tubular bone of extremity. The early surgical management before the fracture is important and has many benefits: avoiding terrible pain and complications, relatively easy surgery, reducing rehabili‐ tation time and life-threatening condition. The surgical methods for bony metastasis include curettage and bone cement (PMMA, polymethyl methacrylate) augmentation, internal fixation with plate or intramedullary (IM) nail, arthroplasty, and prosthesis reconstruction. The surgical treatment method is chosen by multidisciplinary teamwork. The most appropriate surgical option should be selected under the consideration of patient's age and life expectancy, general condition, response of medical treatment, and even preoperative life quality, because major surgery lead to stop or delay of chemotherapy and radiation therapy, and many

Recently, various minimally invasive surgical methods that can be performed without general anesthesia and large incision have been introduced for metastatic bone tumor: ethanol injection, cryoablation, radiofrequency (RF) ablation, cementoplasty, etc. The percutaneous bone cement (PMMA, polymethyl methacrylate) injection is known as cementoplasty or osteoplasty, and has been shown favorable outcomes in the vertebral body and the flat bones such as pelvis, scapula, and sternum. However, solitary bone cement injection without metallic

A new novel surgical technique will be introduced in the concept of percutaneous metallic fixation and simultaneous bone cement injection. For this technique, the unique implant, multihole injection screw and nail, is developed. This implant has a hollow in the center and perforated side holes allowing the material injection to the bony lesion. This minimally invasive surgical method showed good result in the respect of pain relief, mechanical stability, surgical risk, rehabilitation period, hospital stay, surgical cost, and local tumor suppression. The injection material can be various, including chemotherapeutic agent, anti-osteolytic agent, and accelerate bone healing agent as well as PMMA bone cement. Recently, the MR-guided focused ultrasound surgery (MRgFUS) is introduced. MRgFUS is an external ablation which showed effectiveness in reducing pain from bone metastases. However, MRgFUS lacks

This chapter will introduce the diverse developing minimally invasive surgical methods and suggest future direction for better management of patients with metastatic bone tumor.

fixation at the long bone still has high risk of pathologic fracture.

threatening to patients.

128 Tumor Metastasis

accompanied complications.

restoration for mechanical stability.

for palliation but has limitation of bone strengthening.

Laser ablation is the application of thermal energy converted from light energy. Thermal energy will be diffused into the tumor tissue, inducing cellular coagulation necrosis through denaturation of cellular protein. For this technique, a neodymium: yttrium aluminum garnet (Nd:YAG) type generator or diode is used at lower power for thermal effect (photocoagulation) or at higher frequency (vaporization and cavitation).

The procedure time is short (about 10 minutes) and the extent of tumor necrosis is related to the amount of deposited energy, up to 15 mm in diameter for 1200 J. In the case of photocoa‐ gulation, laser ablation has been a useful method to treat benign primary bone tumor osteoid osteoma because of its accuracy, reliability, and accessibility. However, photocoagulation is not appropriate to treat large lesions [1].

The current use of laser ablation for metastatic bone cancer is limited; the laser technology cannot cover large lesion and takes long time to be done percutaneously.

### **2.3. Radiofrequency (RF) ablation**

Radiofrequency ablation is a procedure to damage tumor cell through heat generated from an active electrode inserted into the tumor. For effective treatment, the procedure is performed at a temperature between 60°C and 100°C for 5–10 minutes.

Different size of a single tip electrode, which ranges from less than 15 mm up to 50 mm in diameter, determines the removable size of tumor. To treat larger volume of tumor, additional electrode should be inserted: internally cooled electrodes for cooling system and pulsed mode, perfused electrode, which increases tissue conductivity, or umbrella-shaped electrode and multipolar arrays which increases electrode tip coverage.

Radiofrequency ablation has been widely used to treat soft tissue cancer including hepatocel‐ lular carcinoma and thyroid cancer. In the skeleton, this method is used both as curative treatment for benign bone tumor such as osteoid osteoma, and palliative treatment for metastatic bone tumor [1]. **Figure 1** illustrates an operation case for bone metastasis by RF ablation.

**Figure 1.** RF ablation can be applied for the pelvic bone metastasis.

### **2.4. Cryoablation**

Liquid nitrogen has been used as an intraoperative adjuvant method in the open bone tumor surgery. For the percutaneous application, technical progress was made for probe manufac‐ turing, and utilization of argon gas as a cryogen. The argon gas freezes the tumor tissues at −100°C around the active probe, forming ice balls around the probe. Temperature below −20°C leads to cellular necrosis causing protein denaturation and rupture of cell membranes.

In general, the size of the necrosis is likely to be smaller than the ice ball and its maximum is up to 3 cm in diameter. The forming ice ball can be monitored by ultrasonography or computer tomogram but cannot be detected by fluoroscopy. Processes of the cryoablation are categorized into three phases: a first freezing phase (10 minutes), a thawing phase with helium gas (5 minutes), and a second freezing phase (10 minutes). Cryoablation is commonly used to treat prostate cancer. Treating metastatic bone tumor using cryoablation, however, may not be a good choice; the method fails to cover its big sizes, takes a long time, and is unable to perform moving tip technique [1]. **Figure 2** illustrates a treatment for femoral neck metastasis by cryoablation.

**Figure 2.** Cryosurgery with probe type rod is applied for femoral neck metastasis.

#### **2.5. MRI-HIFU (high-intensity focused ultrasound) ablation**

HIFU induces coagulation necrosis of the tumors by focusing high heat transformed from ultrasound produced by a transducer on tumors.

HIFU ablation has been a treatment for uterine myoma as well as palliation of bone metastases and sarcomas. The biggest advantage of HIFU ablation is its noninvasive procedure (however, the development of its interstitial applicators is in progress). In addition, HIFU ablation can eliminate tumors clearly and promptly: about 15 mm in diameter along the axis of the beam and about 1.5 mm in transverse diameter. Its procedure is conducted under MR or US guidance [1].
