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IN THE SPOTLIGHTS Highlight from EPL Modelling the effect of microwave ablation Microwave ablation is gaining popularity as an efficient therapeutic option for treating cancerous tumor cells in patients who are non-surgical candidates. It is a minimally invasive treatment with a short recovery time. Modelling the effect of the treatment helps to minimise damage of healty tissues. Microwave ablation (MWA) is a material-specific responsiveness procedure with the advantage of faster ablation times, larger ablation volumes, and potentially strong deactivations for tumors compared to other thermal ablation methods. However, the interaction of the medical tools with the tissue may result in healthy tissue damage which can be eliminated by clarifying the causation and conditions of their development. To ensure the destruction of cancer cells with minimal damage to healthy tissue, the elevation of temperature and the evolution of the necrotic tissue need to be controlled. Besides experimental methods, computer modeling is proven to be an effective approach for improving the performance of MWA. Moreover, since the thermal spread in biological tissue is difficult to measure, generating the predictive models from procedural planning to execution may provide a great impact on patient care. Due to complexity and computational resources consumption, most of the existing numerical models are two-dimensional axisymmetric to emulate actual three-dimensional cancers and surrounding tissue. A mathematical model for the simulation of MWA should consist of three essentials components. The first component includes the model of the antenna that generates a microwave field in the tissue. The second component deals with the heat distribution in the tissue including sources and sinks and the phase changes. The third part describes the effect of heat on tumor cells and their destruction. All these components of the ablation model depend on the dielectric properties and thermal parameters of tissues as well as a variety of material parameters. Additionally, the inclusion of the temperature dependence of dielectric properties, the heat capacity, thermal conductivity, and blood perfusion, is pivotal for establishing the correct model of the ablation process. Although MWA operates in the frequency range from 915 MHz to 2.45 GHz, the antenna system at 2.45 GHz produces greater power deposition and larger ablations in a shorter time due to matching the frequency with water molecule resonance. Microwave power radiated from the antenna is absorbed by surrounding tissue, leading to heating the targeted tissue, consisting of the m FIG. 1: a) Temperature [oC] distribution and b) fraction of damage of liver, lung, kidney, and bone tissue after 600s of exposure to microwave frequency of 2.45 GHz and the input power of 10 W. The black circle shows the boundary of the tumoral tissue. tumor and a margin of surrounding tissue. It was found that temperatures above 60°C cause relatively instantaneous cell death, while temperatures from 50 to 60°C will induce coagulation and cell death in a matter of minutes, typically 10 min. In our study, calculations were performed for liver (high perfusion and large heat sinks), lung (low conductivity and large heat sinks), kidney (high perfusion and large heat sinks), and bone (low conductivity) tissue by using the Comsol Multiphysics simulation package. The temperature distribution has an ellipsoidal shape reaching the highest values near the antenna slot as illustrated in Figure 1a. With increasing the distance from the antenna, the heat source becomes weaker and the perfusion of blood limits the extent of the heated area. The highest and the lowest values of the temperature correspond to the kidney and bone tissue, respectively. Ablation zones are concentrated around the tip and slot of the antenna as shown in Figure 1b. The necrotic tissue is mainly located in the tumor with a small amount of surrounding tissue being damaged. Microwaves are less susceptible to perfusion or heat sinks so they successfully penetrate deep into low-conductivity materials such as lungs and bone. The obtained results indicate that the simulation technique can be useful for predicting optimal conditions for MWA and should be considered in treatment planning. n Reference [1] M. Radmilovi-Radjenovi et al., EPL 136, 28001 (2021) 10 EPN 53/3
HIGHLIGHT FROM EPJ PLUS IN THE SPOTLIGHTS Impact of medical and imaging physics on the COVID pandemic The COVID pandemic has had a profound global impact, a new collection of papers looks at a multidisciplinary approach to aspects of the pandemic. The COVID pandemic has impacted every aspect of our lives over the past two years. It is little surprise then that this crisis has united a wealth of disparate fields of science in attempts to mitigate the virus and its effects. A new focus issue of EPJ Plus collects together invited papers that detail the impact of medical imaging and medical physics technology on various aspects of the COVID pandemic. The focus issue is guest-edited by Evaristo Cisbani and Franco Garibaldi, both from Istituto Superiore di Sanita, Rome, and Istituto Nazionale di Fisica Nucleare, Rome, along with Stephanie Majewski, UC Davis, California, USA, and Andrea Gori, University of Milano, Italy. “The focus issue deals with Molecular imaging techniques applied to Covid 19. This is just the right time for such a collection, as we believe we have now accumulated enough data and information,” Garibaldi says. “We have had the problem of COVID for the last two years and we must be prepared for possible future pandemics.” One particular aspect of the COVID infection looked at by the collection and its authors is inflammation. This is one of the primary causes of severe sickness, especially in those with underlying health conditions such as diabetes. In their Editorial, the guest editors of the focus issue say that new advanced technologies already available in the research field and undergoing constant improvement could translate into increased sensitivity of early detection and avoiding the longterm side effects of inflammation. The key to this is understanding what actually needs to be imaged or visualised and what the emerging imaging needs are. Thus, the editors asked experts to address the biomedical issues related to the COVID-19 pandemic and associated inflammatory effects. The editors lay out the multidisciplinary focus points for the topical collection papers as: the origin and evolution of COVID infection from a biological perspective, diagnosis and early differentiation of COVID-19 from other diseases, and the role of advanced detection technology including medical physics and artificial intelligence. n Reference [1] Focus Point Issue “Progress in medical physics in times of CoViD-19 and related inflammatory diseases”, Guest Editors: E. Cisbani, F. Garibaldi, S. Majewski, A. Gori, Eur. Phys. J Plus (2022) FIG. 1: Top: T-cells can be detected by a PET scan of the total body (courtesy of UC Davis EXPLORER group); bottom: 18F-FDG PET scan shows unsuspected pulmonary thrombi in COVID-19 patients. EPN 53/3 11
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