The Philips Sonalleve HIFU system is expected to be efficacious in reducing pain scores in patients with painful osteoid osteoma and other benign bone tumors, and in reducing their pain medication usage. No serious adverse effects are expected to result from this treatment.

The objective of this study is to determine if MR-guided high-intensity focused ultrasound (MR-HIFU) is safe and effective technique for alleviating the pain associated with osteoid osteoma and other benign bone tumors in paediatric patients and adults(up to age 40 yrs). This technique meant to be an alternative to the standard-of-care, radiofrequency and laser-based percutaneous ablation. Safety of the technique will be assessed through evaluating non-targeted heating using MRI based temperature mapping. and inspecting patients post treatment for skin burns or other signs of serious adverse events. Efficacy of the technique will be assessed by evaluating/recording patients observed pain, quality of life, and pain medication usage both before and up to 6 months following treatment.

Inclusion Criteria:

• Age 5-40 years.
• Able to give informed consent and have parent or guardian give informed consent if applicable.
• Weight <140 kg (requirement to fit safely on top of the HIFU table and inside the MRI).
• Definitive radiographic & clinical presentation of osteoid osteoma or other benign tumor lesion(avoiding need for biopsy).
• Pain specifically at the site of interest target lesion.
• Pain score for target lesion >/= 4 (indicating at least moderate pain) or an age-appropriate pain scale.
• Target lesion is uncomplicated (i.e. no fracture/spinal cord compression/cauda equina syndrome/soft tissue component).
• MR-HIFU treatment date >/= 2 weeks from most recent surgical treatment of lesion.

Exclusion Criteria:

• Unable to characterize pain specifically at the site of interest (target lesion).
• Pregnant/nursing females.
• Target lesion is complicated (i.e. presence of one of fracture/spinal cord compression/cauda equina syndrome/soft tissue component).
• Target lesion < 1cm from neurovascular bundles/bowel/hollow viscera or regions of cartilage/ bone growth).
• Target lesion located in skull, spine (excluding sacrum, which is allowed) or sternum.
• Scar along proposed HIFU beam path.
• Orthopaedic implant along proposed HIFU beam path or at site of target tissue.
• Serious cardiovascular, neurological, renal or haematological chronic disease.
• Active infection.
• Contraindication to general anaesthetic or gadolinium MRI contrast agent.
• Requirement for general anesthesia for non-HIFU related MRI's.