# Using the Tissue Impulse Response Function to Streamline Fractionated MRgFUS-Induced Hyperthermia

## TL;DR

This paper introduces a streamlined method for using focused ultrasound to deliver heat therapy for cancer, reducing the need for costly MRI monitoring.

## Contribution

A new off-line method using the tissue impulse response function to control hyperthermia without continuous MRI feedback.

## Key findings

- The method achieved stable hyperthermia of +7 °C for 15 minutes in tissue-like models.
- It outperformed traditional MRI feedback methods in temperature stability and was robust to noise in clinical data.

## Abstract

This research explores a new method for combining radiation therapy with a special type of heat treatment (hyperthermia) aimed at making cancer treatments more effective. Probing tissues with focused ultrasound guided by MRI, we can subsequently deliver controlled, gentle heat to targeted areas without needing continuous MRI monitoring, which is often expensive and time-consuming. This study tested the method on tissue-like models and showed that it consistently reaches and maintains the desired temperature more reliably than traditional methods. This advance could make hyperthermia more accessible in cancer treatment by streamlining the process and reducing costs, offering a practical way to enhance the effects of radiation therapy. Ultimately, this approach may broaden hyperthermia’s use in hospitals, providing the research community and clinicians with a reliable, cost-effective tool for improving patient care in oncology.

Background/Objectives: Combining radiation therapy with mild hyperthermia, especially via magnetic resonance-guided focused ultrasound (MRgFUS), holds promise for enhancing tumor control and alleviating symptoms in cancer patients. However, current clinical applications of MRgFUS focus primarily on ablative treatments, and using MRI guidance for each radiation session increases treatment costs and logistical demands. This study aimed to test a streamlined workflow for repeated hyperthermia treatments that reduces the need for continuous MRI monitoring, using an approach based on impulse response function (Green’s function) to optimize acoustic power settings in advance. Methods: We implemented the Green’s function approach in a perfused, tissue-mimicking phantom, conducting 30 experiments to simulate hyperthermia delivery via MRgFUS. Pre-calculated acoustic power settings were applied to maintain a stable hyperthermia target without the need for real-time feedback control from MRI thermometry. Additionally, a retrospective analysis of patient thermometry data from MRgFUS sonications was performed to assess feasibility in clinical contexts. Results: Our experiments demonstrated consistent, stable hyperthermia (+7 °C) for 15 min across varying perfusion rates, outperforming conventional closed-loop MRI feedback methods in maintaining temperature stability. The retrospective analysis confirmed that this method is noise-robust and clinically applicable. Conclusions: This off-line approach to hyperthermia control could simplify the integration of MRgFUS hyperthermia in cancer treatment, reducing costs and logistical barriers. These findings suggest that our method may enable the broader adoption of hyperthermia in radiation therapy, supporting its role as a viable adjuvant treatment in oncology.