Iterative time-reversal for multi-frequency hyperthermia

Massimiliano Zanoli,Hana Dobšíček Trefná

doi:10.1088/1361-6560/abd41a

Massimiliano Zanoli, Hana Dobšíček Trefná

Open Access

https://doi.org/10.1088/1361-6560/abd41a

Copy DOI

Abstract

Time-reversal (TR) is a known wideband array beam-forming technique that has been suggested as a treatment planning alternative in deep microwave hyperthermia for cancer treatment. While the aim in classic TR is to focus the energy at a specific point within the target, no assumptions are made on secondary lobes that might arise in the healthy tissues. These secondary lobes, together with tissue heterogeneity, may result in hot-spots (HSs), which are known to limit the efficiency of the thermal dose delivery to the tumor. This paper proposes a novel wideband TR focusing method that iteratively shifts the focus away from HSs and towards cold-spots from an initial TR solution, a procedure that improves tumor coverage and reduces HSs. We verify this method on two different applicator topologies and several target volume configurations. The algorithm is deterministic and runs within seconds, enabling its use for real-time applications. At the same time, it yields results comparable to those obtained with global stochastic optimizers such as Particle Swarm.

Highlights

In deep microwave hyperthermia (MW-HT) for cancer treatment, a conformal array of antennas, called applicator, is used to non-invasively and selectively increase the temperature of a deep-seated tumor up to 40 °C–44 °C for approximately one hour (Elming et al 2019, Paulides et al 2020)
Starting from the classic TR solution, the hot-to-cold spot quotient (HCQ) is progressively minimized until no further improvement is achieved by either cold- or HS iterations
The proposed iterative TR (i-TR) beam-forming technique is shown to deliver hyperthermic treatment planning (HTP) solutions equivalent to those provided by global optimizers such as particle swarm (PS), while being orders of magnitude faster

Summary

Introduction

In deep microwave hyperthermia (MW-HT) for cancer treatment, a conformal array of antennas, called applicator, is used to non-invasively and selectively increase the temperature of a deep-seated tumor up to 40 °C–44 °C for approximately one hour (Elming et al 2019, Paulides et al 2020). The challenge in MW-HT is to reach deep-seated targets with adequate power deposition while keeping the nearby healthy tissues (HSs) below a safety temperature threshold. The power loss in these tissues can cause hot-spots (HSs), which effectively limit the maximum temperature achievable in the target This can prevent the treatment from reaching high therapeutic thermal doses (Paulides et al 2010, Kok et al 2017). Other HSs might arise deeper in the body due to the anatomical heterogeneity and interfaces between tissues with different dielectric properties, together with the imperfect interference pattern generated by the phased array In such cases, the pattern has to be improved by means of amplitude and phase steering of the applicator array, with parameters obtained by a hyperthermic treatment planning (HTP) step (Gavazzi et al 2020)

Methods

Results

Discussion

Conclusion