Clinical neurological HIFU applications: the Zurich experience

High intensity focused ultrasound (HIFU) allows for precise thermal ablation of target tissues. It can penetrate the human body non-invasively and produce physiological effects in diseased tissue deep inside the body while sparing healthy tissue on the trajectory to and around the target. While this treatment modality is by now well established for various types of extra-cranial soft tissue tumors, it has only recently been acknowledged as a novel method for non-invasive neurosurgery of the brain. Transcranial HIFU under MR imaging guidance has been particularly successful in functional neurosurgery, where currently a multi center clinical phase II trial is under way to assess its safety and efficacy profile in the treatment of Essential Tremor. Its clinical introduction as an image guided, non-invasive treatment modality for malignant brain tumors, however, has been delayed for various technical and procedural difficulties inherent to both the applied technology and the targeted class of interventions. Building on the accumulated experience from treating more than 30 patients suffering from chronic pain, Essential Tremor, Parkinson’s Disease and Dystonia with transcranial MR imaging guided Focused Ultrasound a new attempt was launched in Zurich in 2010 to include brain tumors into the treatment spectrum of HIFU. A clinical phase I trial was initialized to assess the feasibility and safety of treating patients suffering from centrally located, freshly diagnosed or recurrent gliobastoma, or brain metastases of breast and lung cancers using the InSightec ExAblate Neuro platform, the only system available at this time for clinical application of HIFU in the human brain. The preliminary technical and clinical results of the three treatments conducted so far in this ongoing study demonstrate that non-invasive focused ultrasound interventions for brain tumors can indeed be safely carried out and can create clinical benefits for the patient. These encouraging results reinforce the huge expectations towards HIFU as a new core technology for neurological applications and justify the scientific efforts invested into the field. However, the practical experience also shows that the gap to widespread clinical application is still huge and that substantial technical challenges remain to be overcome in order to fully harvest the potential of the technology. This might not be an easy task as image guided HIFU therapy is by definition multimodal, might include combined therapy device approaches and will require truly interdisciplinary research through a wide range of natural science, medicine and engineering disciplines.