Ultrasound is a form of energy that passes through skin, muscle, fat and other soft tissue so no incisions or inserted probes are needed. High intensity focused ultrasound energy, when focused on a small target volume, provides a therapeutic effect by raising the temperature of the target high enough to destroy it. Only tissue at the target is heated well above the temperature needed to kill the tissue, with no damage to the tissue outside of the target.

The ExAblate® system is fully integrated to a Magnetic Resonance imaging scanner. The whole procedure is conducted inside the imaging scanner. During this procedure, the ExAblate® will use the MR imaging for planning your treatment, treatment delivery guidance and therapy feedback during the treatment of the bone metastasis (Figure 1).

Why do doctors use it?

Your referring doctor has determined that your pain from your bone metastasis has not responded to radiation therapy, or you are not a good candidate to receive standard radiation, or you may have informed your doctor that you do not want radiation therapy. The ExAblate® treatment, which is non-invasive and does not use ionizing radiation for treatment, is one of the therapies that is available to your doctor to offer. Based on the clinical study that served to gain FDA approval for the treatment, the procedure has a very good chance to help your condition. Additionally, it may allow you to reduce your pain medications, which could help reduce their side effects, and better your quality of life.

Our expert on MRgFUS treatment of bone metastases will discuss the full risks and benefits of this procedure with you.

Am I suitable for the ExAblate® treatment? – Treatment criteria

• Locations of treatable tumors include the ribs, sternum, extremities, pelvis, shoulders, and posterior aspects of the lower lumbar spine, sacrum, and coccyx.
• Tumors must be visible on MRI.
• Tumors must be accessible to the focused ultrasound beam; for example, tumors blocked by extensive scarring or bowel cannot be treated.
• The targeted bone must be at least 1 cm from the skin surface.

Am I suitable for the ExAblate® treatment? – Contraindications

ExAblate® MRgFUS is not suitable for all patients. Patients who have any of the following should inform their doctor so that he or she can make good treatment choices with you.

• If you cannot safely undergo MR imaging, you may not be a good candidate for the procedure. For example, any metallic implants must be non-magnetic to prevent injury to the patient from the MR's strong magnetic field.
• If your physician has told you that you have a bone that is fragile and may break or needs surgery to be stabilized, or has already been stabilized with surgical implants, you may not be a good candidate. The cancer itself as well as cancer treatments may cause the bone to weaken and fracture.
• If you have extensive skin scarring in the areas that would be treated, you may not be a good candidate for the procedure.

Please discuss all of these conditions with your physician so your doctor can properly evaluate your suitability for the ExAblate® therapy.

Risks of having this done

Infrequent complications have been reported following ExAblate® MRgFUS treatments. These risks are described below.

Short Term Risks - Day of Treatment up to 2-Weeks Post-Treatment

The most common potential risks associated with the ExAblate® procedure is pain and discomfort (mild, moderate and severe) related to the delivery of the ultrasound energy to the bone; this dissipates shortly after the sonication (approximately less than 1 minute) and can be managed with judicious use of anesthetic, analgesic and sedative medications administered by your physician. Occasionally, patients may experience post-procedure pain which usually resolves within a few days. Other risks include position-related pain due to the position you must maintain during the entire treatment process; this can appear up to 1-3 days after treatment and should resolve quickly. This can be minimized by careful positioning at the start of the procedure to support the rest of the body in a comfortable position during the treatment.

If there is improper acoustic coupling (i.e., the interface between the body and the transducer gel pad has gaps), then there is a possibility of skin burn. These events are acute, occurring on the day of treatment with red skin patches or even 2nd-3rd degree burns. This risk is minimized by ensuring the skin around the area of the treatment is free of any hair and cleaned with alcohol prior to treatment. In addition, these events may be further minimized by communication with your doctor when you first feel skin pain. Mild to moderate skin burns should heal and fade within 7-14 days.

If a nerve was located close to the designated area for ablation or close to a bone in the far beam path, you may feel pain during sonications, or numbness, or pain immediately after the treatment or during the following few days. If you experience pain in a nearby area during the sonication, you should tell your physician so he or she can check for the presence of nearby nerves in the beam path.

You may experience a blood clot during the procedure because of the prolonged stationary position required for treatment, and you may have complications related to the clot if it is not treated quickly. Venous clots can travel to other part of the body and cause heart, brain, or lung damage.

You may experience a fever within a few days after the procedure if a large amount of tissue has been ablated. If your temperature goes above 100°F for 24 hours, you should call your physician.

You may see blood in your urine or have a bladder or kidney infection because of the catheter used to drain your bladder during the procedure, but it should resolve completely. If you get a urinary tract infection, you may need antibiotics.

You may have bruising in the area of the intravenous catheter following the procedure, similar to that experienced after blood draws. This should resolve within a week.

You may feel tired for several days after the procedure because of the exertion to remain still for so long.

Long Term Risks - Longer than 2-Weeks Post-Treatment

Overall, ExAblate® MRgFUS is a reasonably safe procedure for treating painful bone metastases with minimal risk. Infrequent complications that have been reported following ExAblate® treatment include the possibility of scar formation after skin burn and possible numbness. If a nerve was damaged (unintended), there may be muscle weakness, numbness, or sensory loss that may resolve after several months, or it may be non-reversible. In the clinical study for ExAblate® treatment for bone metastases, this occurred in one patient treated with the ExAblate® treatment.

If you experience a blood clot after the procedure that is not treated emergently, you may have long term complications related to it if it does not resolve quickly. You could have muscle, heart, brain, or lung damage. Bone fractures may occur at any time as a result of the bone metastases weakening the bone, prior radiation therapy, or the ExAblate® procedure.

Benefits of having this done

The pivotal study for this device was conducted under an investigational device exemption and the results are published on Clinicaltrials.gov (NCT00656305). This was a global study conducted at 17 centers located in the US, Canada, Israel, Rome, and Russia. The study design included randomization into a treatment arm and a placebo arm in a 3:1 ratio.

A total of 139 subjects took part in the study. The post treatment follow up was through 3 months. The primary endpoint was clinically significant pain relief and stable or reduced pain medication usage; secondary endpoints were related to improved quality of life. After 3 months of follow-up, 65% of patients experienced substantial pain relief at the site of ExAblate® treatment. Pain relief was observed within 3-7 days after the procedure and coincided with improvement in quality of life. The procedure is non-invasive (i.e., no surgical scars) and may be performed on an out-patient basis.

How to decide about this treatment

You must explain all of your medical conditions to your physician as well as the level of pain that you are experiencing. Your physician will evaluate whether you are a good candidate for the ExAblate® treatment. Together, in consultation with your physician and caregivers, you will need to decide if you are a suitable candidate. Your physician will also discuss any other treatment options that are available to you.

Where to find out more

Patient testimonials

Glossary

MRgFUS	Magnetic Resonance guided Focused Ultrasound Surgery
Bone Mets	abbreviated term for bone metastasis
Metastasis	spread of main cancer to other locations in the body, including to the bone
Sham/placebo	used in a clinical trial to demonstrate effectiveness against a known standard which would be No Treatment
Randomized	Method used to assign subjects to a treatment arm of the study so that the actual treatment allocation remains unknown to participating subjects until the end of the study
Sonication	a pulse of ultrasound energy delivered over a period of 10-20 seconds