MRI-controlled focused ultrasound hyperthermia in bone for thermally mediated drug delivery

INTRODUCTION: Thermosensitive liposomal drug carriers provide a method for triggering the rapid release of high drug concentrations in a targeted region [1]. In patients with painful bone metastases, this could increase the effectiveness of thermal approaches to pain palliation by increasing cell kill in treatment margins, and reducing the required energy deposition, potentially reducing treatment time and the potential for normal tissue damage. MRIcontrolled focused ultrasound can achieve noninvasive heating in a number of soft tissues, but temperature control in bone is made difficult by the inability of PRF thermometry to measure temperature in bone, and due to preferential heating at the bone interface due to high ultrasound absorption of bone. While chemical shift imaging techniques for bone marrow thermometry have been described [2], conventional PRF thermometry can be used to maintain desired temperatures in bone by controlling the treatment based on temperatures measured in the soft tissue immediately in front of the bone interface, as temperatures here are expected to be similar to those in the bone [3]. The objective of this work is to demonstrate the feasibility of MRIcontrolled FUS hyperthermia in bone, and its potential use in localized drug delivery from thermosensitive liposomes.