Pain palliation in patients with bone metastases using magnetic resonance-guided focused ultrasound with conformal bone system: a preliminary report

Abstract

Purpose: We evaluated the safety and effectiveness of the Magnetic Resonance-guided Focused Ultrasound (MRgFUS) with the ExAblate Conformal Bone System for the palliation of painful bone metastases.

Materials and methods: Our Institutional Review Board approved this study, and all patients gave informed consent prior to enrollment. A total of six painful metastatic bone lesions in five patients were treated using MRgFUS with the ExAblate Conformal Bone System for pain palliation. The follow-up sessions were at 3 days, 2 weeks, 1, 2, and 3 months, and 1 year after treatment. Efficacy was evaluated by the changes in visual analog scale (VAS) scores. At 3-months and 1-year follow-ups, unenhanced computed tomography and contrast-enhanced MR imaging examinations were performed. All adverse events were assessed to evaluate treatment safety.

Results: All patients showed significant pain relief within 2 weeks. Two patients experienced complete pain reduction that lasted for 1 year. Two other patients showed pain relief measured as VAS scores of 2 and 4 on their last follow-up. Although the remaining patient had experienced significant pain relief in two lesions, the VAS score re-increased on his last follow-up. The size of the enhancing soft tissue mass in metastatic lesions decreased, and new bone formation was seen on follow-up images. Although adverse events were not serious, non-specific leg pain and second degree skin burn were noted.

Conclusion: MRgFUS was demonstrated to be effective palliative treatment within 2 weeks in selected patients with painful bone metastases.

Keywords: Magnetic Resonance-guided Focused Ultrasound; bone metastases; high-intensity focused ultrasound; pain palliation.

Fig. 1

Procedure image. The continuous MR imaging system allows the physician to identify and target tumors and provides temperature monitoring of the treated tissue in real time.

Fig. 2

Patient 2 with breast cancer. Comparison of (A) contrast-enhanced T1-weighted MR image before treatment, (B) contrast-enhanced T1-weighted MR image at 90 days after treatment; note the decrease in size of the enhancing mass, especially right to left diameter. Comparison of (C) CT before treatment, (D) CT at 90 days after treatment; note the new bone formation (arrow). Further new bone formation (arrow) was seen on (E) CT at 1 year after treatment.

Fig. 3

Patient 3 with breast cancer. Comparison of (A) contrast-enhanced T1-weighted MR image before treatment, (B) contrast-enhanced T1-weighted MR image at 90 days after treatment; note the newly-developed linear, non-perfused area (arrows) at the anterior periosteum of the femur.