ARTICLE IN PRESS JID: JJBE [m5G;June 21, 2017;10:8] Medical Engineering and Physics 000 (2017) 1–8 Contents lists available at ScienceDirect Medical Engineering and Physics journal homepage: www.elsevier.com/locate/medengphy Microwave thermal ablation: Effects of tissue properties variations on predictive models for treatment planning Vanni Lopresto a,∗ , Rosanna Pinto a , Laura Farina b , Marta Cavagnaro b a ENEA, Division of Health Protection Technologies, Casaccia Research Centre, Rome, Italy b DIET, Sapienza University of Rome, Rome, Italy a r t i c l e i n f o Article history: Received 3 June 2016 Revised 16 April 2017 Accepted 1 June 2017 Available online xxx Keywords: Microwave thermal ablation Tissue electromagnetic properties Numerical modelling Bio-medical applications of electromagnetic fields a b s t r a c t Microwave thermal ablation (MTA) therapy for cancer treatments relies on the absorption of electromag- netic energy at microwave frequencies to induce a very high and localized temperature increase, which causes an irreversible thermal damage in the target zone. Treatment planning in MTA is based on exper- imental observations of ablation zones in ex vivo tissue, while predicting the treatment outcomes could be greatly improved by reliable numerical models. In this work, a fully dynamical simulation model is exploited to look at effects of temperature-dependent variations in the dielectric and thermal properties of the targeted tissue on the prediction of the temperature increase and the extension of the thermally coagulated zone. In particular, the influence of measurement uncertainty of tissue parameters on the numerical results is investigated. Numerical data were compared with data from MTA experiments per- formed on ex vivo bovine liver tissue at 2.45 GHz, with a power of 60 W applied for 10 min. By including in the simulation model an uncertainty budget (CI = 95%) of ±25% in the properties of the tissue due to inaccuracy of measurements, numerical results were achieved in the range of experimental data. Obtained results also showed that the specific heat especially influences the extension of the thermally coagulated zone, with an increase of 27% in length and 7% in diameter when a variation of −25% is considered with respect to the value of the reference simulation model. © 2017 IPEM. Published by Elsevier Ltd. All rights reserved. 1. Introduction Microwave thermal ablation (MTA) procedures for the treat- ment of pathologic tissues rely on the generation of very high tem- peratures (55–60 °C at minimum) in the target zone owing to the absorption of electromagnetic energy at microwave (MW) frequen- cies (typically 915 MHz or 2.45 GHz). At temperatures of about 55– 60 °C and above, an almost instantaneous cell death is achieved; at lower temperatures coagulation can be induced heating the tissue for a longer time, e.g., at 50 °C less than 5 min are needed to ob- tain irreversible cellular injury, whereas at least 60 min are needed at 46 °C [1,2]. MTA has remarkably developed in the last years, showing many promising advantages over surgical techniques for local treatment of soft-tissue pathologies, e.g. tumours. These ad- vantages are mainly linked to the limited invasiveness of the ap- plicators, which are typically interstitial antennas inserted into the body percutaneously or following natural paths (e.g. veins or ori- fices) up to the target area [3]. ∗ Corresponding author. E-mail address: vanni.lopresto@enea.it (V. Lopresto). In tumours ablation procedures, treatment planning is based on the proper insertion of the antenna into the targeted tu- mour while avoiding vascular structures, usually exploiting image- guidance techniques, as well as on the MW power (with intensities up to 100 W) to be radiated and the duration (typically about 5– 20 min) needed to achieve an ablated zone (also named thermal lesion) that is sufficiently wide to cover all the cancerous tissue plus a 5–10 mm safety margin of surrounding healthy tissue [2]. Nevertheless, there are still open issues under investigation related to the changes in the physical properties of tissues, both during the procedure and for inter-patient variability, and to the presence of very complex phenomena as, e.g., the shrinkage of the tissue [4–6]. These gaps in knowledge in predictive simulations weaken the reli- ability of the technique, delaying model-based treatment planning integration within the clinical workflow. On the other hand, a full understanding of the changes in the physical properties of tissues during MTA procedures, and of their influence on MTA outcomes, would allow obtaining more reproducible and reliable results. Heating influences the dielectric properties of tissues causing ir- reversible structural changes. In particular, in a temperature range of 60–80 °C, protein denaturation occurs [7,8], while as the temper- ature approaches 100 °C the water content in the tissue drops due http://dx.doi.org/10.1016/j.medengphy.2017.06.008 1350-4533/© 2017 IPEM. Published by Elsevier Ltd. All rights reserved. Please cite this article as: V. Lopresto et al., Microwave thermal ablation: Effects of tissue properties variations on predictive models for treatment planning, Medical Engineering and Physics (2017), http://dx.doi.org/10.1016/j.medengphy.2017.06.008