Bone Pain Control Using MRI and Ultrasound
Saturday, November 15 2008 13:49
Magnetic resonance-guided focused ultrasound surgery (MRgFUS), a noninvasive thermal ablation technique that has been shown to be clinically effective in the treatment of uterine fibroids, is now being evaluated as a method for treating painful bone metastases.
Now physicians in North America are running a full scale clinical trial to see if the method really does work as well or better than traditional pain management methods.
Pioneer studies undertaken in Israel in the past few years using magnetic resonance imaging (MRI) with focused ultrasound have shown that this method offers some patients relief from some of the most intense pain resulting from cancer that has spread to the bones.
"Bone metastases are one of the most common causes of pain for cancer patients," said Dr. King Li, chair of the department of radiology at The Methodist Hospital in Houston, Texas. "Unfortunately, current treatments to relieve this intense pain are very limited."
MRI-focused ultrasound. Dr. Li says, may provide a completely non-invasive way to relieve this type of pain.
Current treatments for severe pain from bone metastases include radiation -- by external beam or by radioactive drugs such as Strontium-89 and Samarium-153 -- or surgery. While these traditional methods may destroy or "ablate" the nerves that transmit pain signals, MRI and ultrasound offers a gentler method.
MRI technology was used in the Houston study to visualize the patient’s anatomy and then to focus ultrasound waves at the targeted tissue.The ultrasound ablates, or destroys, the tissue by means of low-level heat.
The MRI allows the physician to monitor and continuously adjust the treatment in real time, while treating each individual patient (a possible advantage compared to beam radiation, which requires advance planning and rigid execution).
Due to inherent structural characteristics of the bone tissue, it is possible to use a low level of heat and achieve the desired effect, while minimizing damage to adjacent tissue, Li says.
Pain may be substantially reduced for a significant period of time. In earlier clinical studies performed in Israel and Europe, most of the patients reported pain relief within days of treatment.
A large, phase 3 clinical trial is now recruiting patients across the USA and in Toronto and Haifa and Tel Hashomer, Israel.
"This is an important trial because 90 percent of patients with a progressive form of breast cancer have bone metastases and almost all patients with metastatic prostate cancer have tumors that spread to the bones," Dr. Li said.
The U.S. Food and Drug Administration (FDA) approved this technology, magnetic resonance-guided focused ultrasound (MRgFUS), to treat uterine fibroids in 2004. This same technology has already shown promising efficacy and safety results in small studies of pain palliation for patients who have bone metastases. A study in Israel reported in 2007 that 10 out of 13 patients "reported prolonged improvement in pain score and/or reduced analgesic dosage."
Tihe Phase 3 trial, known as ExAblate Treatment of Metastatic Bone Tumors for the Palliation of Pain, is outlined at clinicaltrials.gov
A smaller, non-randomized trial in Toronto and San Diego is ongoing but no longer recruiting patients.
Be aware, patients in the Phase 3 trial are randomized to receive genuine and "sham" ultrasound beam. Patients who are suffering from bone mets might prefer to remain on conventional therapies continuously. The trial sponsors point out:
"Treatment with external beam radiation therapy (EBRT) is the standard of care for patients with localized bone pain, and results in the palliation of pain in the majority of these patients. More than 66% of patients with a limited number of well-localized bony metastases can be treated effectively by external-beam irradiation. However, approximately 30% of patients treated with radiation therapy do not experience pain relief [8, 12-16]. Furthermore, there is an increased risk of pathologic fracture in the peri-irradiation period due to an induced hyperemic response at the periphery of the tumor. This weakens the adjacent bone and increases the risk of spontaneous fracture. Adding to this, patients who have recurrent pain at a site previously irradiated may not be eligible for further radiation therapy secondary to limitations in normal tissue tolerance. The speed of response to radiation therapy varies; from the patients that respond most symptomatic bony metastases begin to respond over the course of 10 to 14 days, 70% of patients experience some pain relief within 2 weeks of starting therapy and, within 3 months 90% of patients achieve pain relief.
"Patients, who had EBRT and failed to improve, may need to seek other therapies such as radio frequency ablation, surgical resection, etc., which are less efficient and have higher treatment related morbidity. Because the ExAblate system is designed to non-invasively ablate tissue, ExAblate may meet the need of these EBRT failed patients. The ExAblate system has the potential to achieve the first three of the four above mentioned goals, as well as changing the treatment limits and resulting morbidity in accordance with the above-mentioned goals [17]. The palliative effect of ExAblate is achieved by heating the bone periosteum, thus ablating the sensory origin of the pain."
Results from the pilot study are outlined in detail in this article: MR-guided focused ultrasound surgery (MRgFUS) for the palliation of pain in patients with bone metastases—preliminary clinical experience (Annals of Oncology 2007).
Edited by J. Strax.
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Posted by J. Strax. Last revised November 15, 2008.
