Robust, planning-based targeted locoregional tumour heating in small animals.

OBJECTIVE:To improve hyperthermia in clinical practice, pre-clinical hyperthermia research is essential to investigate hyperthermia effects and assess novel treatment strategies. Translating pre-clinical hyperthermia findings into clinically viable protocols requires laboratory animal treatment techniques similar to clinical hyperthermia techniques. The ALBA micro8 electromagnetic heating system (Med-logix SRL, Rome, Italy) has recently been developed to provide the targeted locoregional tumour heating currently lacking for pre-clinical research. This study evaluates the heat focusing properties of this device and its ability to induce robust locoregional tumour heating under realistic physiological conditions using simulations. Approach. Simulations were performed using the Plan2Heat treatment planning package (Amsterdam UMC, the Netherlands). First, the Specific Absorption Rate (SAR) focus was characterised using a homogeneous phantom. Hereafter, a digital mouse model was used for the characterisation of heating robustness in a mouse. Device settings were optimised for treatment of a pancreas tumour and tested for varying circumstances. The impact of uncertainties in tissue property and perfusion values was evaluated using Polynomial Chaos Expansion. Treatment quality and robustness were evaluated based on SAR and temperature distributions. Main results. The SAR distributions within the phantom are well-focused and can be adjusted to target any specific location. The focus size (full-width half-maximum) is a spheroid with diameters 9 mm (radially) and 20 mm (axially). The mouse model simulations show strong robustness against respiratory motion and intestine and stomach filling (∆T_90≤0.14°C). Mouse positioning errors in the cranial-caudal direction lead to ∆T_90≤0.23°C. Uncertainties in tissue property and perfusion values were found to impact the treatment plan up to 0.56°C (SD), with a variation on T90 of 0.32°C (1 SD). Significance. Our work shows that the pre-clinical phased-array system can provide adequate and robust locoregional heating of deep-seated target regions in mice. Using our software, robust treatment plans can be generated for pre-clinical hyperthermia research.