Methods for MRI-guided treatment of painful bone metastases with Focused Ultrasound

Abstract

Bone metastases are among the most common types of metastases and can be very painful. The current standard treatment for painful bone metastases is local external beam radiotherapy (EBRT) combined with opioids, but it is not always effective. Lately, MR-guided High-Intensity Focused Ultrasound (MR-HIFU) gained interest as alternative, non-invasive, treatment option, that may provide durable pain palliation. The technique allows faster pain relief with respect to EBRT, most likely because of direct ablation of the nerves that cause the pain. The work described in this thesis aimed at improving some technical aspects in the therapy workflow of MR-HIFU procedures on bone metastases. To improve treatment planning, a method has been tested for combined visualization of bone and soft tissues, using synthetic computed tomography (sCT), which produces images with CT-like contrasts from MR data. This allows a more immediate interpretation of the bone distribution in treatment position. To improve temperature monitoring during treatment, a fat thermometry method was interleaved with the clinically available water thermometry method. This method can monitor temperature in targets in mixed water-fat environments, which are often seen with bone metastases. Finally, to improve predictions of the treatment outcome, the dependence of the Energy Density on the Bone Surface (EDBS), a possible predictor of pain relief, on conditions that typically vary between patients has been investigated. It was observed that the thickness of the subcutaneous fat layer in the beam path is an important parameter for the calculation of EDBS.