Abstract No. 56 MR-HIFU Ablation of Pediatric Osteoid Osteoma: Interim Results from Pivotal Trial

Osteoid osteoma (OO) is a benign but painful bone tumor that most commonly occurs in the cortex of long bones of children and adolescents. Magnetic resonance imaging-guided high intensity focused ultrasound (MR-HIFU) allows precise, image-guided and completely non-invasive ablation without ionizing radiation and has been shown by several groups, including ours, to be a good treatment alternative to RFA. Herein we report interim results of an ongoing pivotal trial (NCT04658771). Primary objective of this study is to determine treatment efficacy of MR-HIFU ablation of painful OO in children and young adults. Sixteen patients with symptomatic OO have been enrolled. Fifteen (11M, 4F, 11±4 years) have undergone MR-HIFU ablation on an institutional review board–approved clinical trial. Eleven have completed one year follow up. Pain relief was assessed using Visual Analog Scale (VAS) pain score and pain/medication logs. Quality of life (QOL) was assessed using patient reported outcome measurement tools. Patients were followed at 1 day, 1 week, 1,6, and 12 months. Eleven patients underwent technically successful MR-HIFU ablation without any significant adverse events. The median worst pre-treatment VAS score was 8 (with NSAIDs) and at 1 year post-treatment was 0, which is significant (Wilcoxon, p< 0.0001). Median total SDS scores decreased from 18 to 12 at one year, demonstrating significant improvement in patients' QOL (Wilcoxon, p=0.0166). The Pediatric Pain Interference Short Form (PROMIS) median total standardized t scores decreased by 21.7 at one year, demonstrating decreased impact of pain on various aspects of the patients' life following treatment (Wilcoxon, p=0.0001). The overall patient and parent PedsQL scores showed a significant improvement in several aspects of QOL (Wilcoxon, p< 0.0001). Specifically, the PedsQL sleep score showed a significant improvement in sleep quality amongst all patients (Wilcoxon, p=0.0005). Ten patients underwent follow up contrast-enhanced MRI at 1 year. OO nidus perfusion was reduced or eliminated in 8 of the patients. Soft tissue edema resolved in 9 of 10 patients and bone marrow edema was reduced or resolved in 8 of 10 patients. MR-HIFU has emerged as a non-invasive treatment option for symptomatic OO that is safe and effective. Interim analysis of results from the ongoing pivotal trial add to existing data demonstrating durable pain relief and improved QOL.