Treatment plan verification in MRgFUs for bone metastasis pain palliation

Abstract

Introduction Focused ultrasound are recently introduced as alternative therapy for pain palliation caused by bone metastases. The heat absorption and propagation in the soft tissues and in the bones strongly depends on the correct focalization of the ultrasonic beam through the interfaces. The real-time thermal map provided by the MRI gives to the interventional radiologist the feedback for the online treatment planning. Purpose The present work is focused on the verification of planning therapy system of a MRgFUs system giving a verification of the propagation and the accumulation of the temperature in bones in particular for the pelvic bone. Materials and methods In this work it has been studied the Philips Sonalleve HIFU installed on Ingenia 3T. The thermal maps has been studied on a multi-interface phantom with albumin-agarose gel volumetric detector. The planned volume ablation temperature has been compared with the T2 imaging modification on the phantom. A dedicated software has been developed for the extraction of the thermal image maps from the system and for the evaluation of the cumulative thermal dose. A first approach has been proposed for the evaluation of the plan in term of DVH (dose/volume histogram). Results High impedance interfaces create local depositions of energy along the sonicated surfaces. The plan cumulative dose verification gives constraints to the physicians on sonication cells positioning. Conclusion The MRgFUs feedback planning gives partial information of the heat deposition. The bone phantom is used to evaluate the real cells volume. The de-focalization created by bones demonstrate the needs of preplanning system dedicated to bones treatments.