Generation of treatment plans for Magnetic Resonance guided High Intensity Focused Ultrasound (MRgHIFU) in the liver

In this thesis, the self-scanning method is proposed to handle organ motion. It takes advantage of the perpetual respiratory motion to passively scan the tumor. In other words, we are placing the static focal point of the HIFU into the tumor. The motion caused by breathing shifts the tumor through this focal point. We anticipate at which time point tumor tissue is located under the focal spot and modulate the HIFU intensity based on this information. Once the tumor has been ablated along the self-scanned trajectory, the focal spot is relocated to a different but static position within the body. With this method, we combine the advantages of the gating and the tracking method: a HIFU device with a fixed focus can be used and a high duty cycle is achieved. Moreover, since with the self-scanning approach no lateral steering of the focal spot is required, fewer secondary lobes are generated and position-dependent decay of the focal spot intensity during lateral steering is avoided. However, this comes at the cost of an increased complexity at the planning stage

Leveraging respiratory organ motion for non-invasive tumor treatment devices: a feasibility study

In noninvasive abdominal tumor treatment, research has focused on minimizing organ motion either by gating, breath holding or tracking of the target. The paradigm shift proposed in this study takes advantage of the respiratory organ motion to passively scan the tumor. In the proposed self-scanning method, the focal point of the HIFU device is held fixed for a given time, while it passively scans the tumor due to breathing motion. The aim of this paper is to present a treatment planning method for such a system and show by simulation its feasibility. The presented planning method minimizes treatment time and ensures complete tumor ablation under free-breathing. We simulated our method on realistic motion patterns from a patient specific statistical respiratory model. With our method, we achieved a shorter treatment time than with the gold-standard motion-compensation approach. The main advantage of the proposed method is that electrically steering of the focal spot is no longer needed. As a consequence, it is much easier to find an optimal solution for both avoiding near field heating and covering the whole tumor. However, the reduced complexity on the beam forming comes at the price of an increased complexity on the planning side as well as a reduced efficiency in the energy distribution. Although we simulate the approach on HIFU, the idea of self-scanning passes over to other tumor treatment modalities such as proton therapy or classical radiation therapy

Self-Scanned HIFU Ablation of Moving Tissue Using Real-Time Hybrid US-MR Imaging

High intensity focused ultrasound (HIFU) treatment in the abdominal cavity is challenging due to the respiratory motion. In the self-scanning HIFU ablation method, the focal spot is kept static and the heating pattern is obtained through natural tissue motion. This paper describes a novel approach for modulating the HIFU power during self-scanning in order to compensate for the effect of tissue motion on thermal buildup