Use of microwave ablation for thermal treatment of solid tumors with different shapes and sizes—A computational approach

Abstract

Microwave Ablation (MWA) is one of the most recent developments in the field of thermal therapy. This approach is an effective method for thermal tumor ablation by increasing the temperature above the normal physiological threshold to kill cancer cells with minimum side effects to surrounding organs due to rapid heat dispersive tissues. In the present study, the effects of the shape and size of the tumor on MWA are investigated. To obtain the temperature gradient, coupled bio-heat and electromagnetic equations are solved using a threedimensional finite element method (FEM). To extract cellular response at different temperatures and times, the three-state mathematical model was employed to achieve the ablation zone size. Results show that treatment of larger tumors is more difficult than that of smaller ones. By doubling the diameter of the tumor, the percentage of dead cancer cells is reduced by 20%. For a spherical tumor smaller than 2 cm, applying 50 W input power compared to 25 W has no significant effects on treatment efficiency and only increases the risk of damage to adjacent tissues. However, for tumors larger than 2 cm, it can increase the ablation zone up to 21%. In the spherical and oblate tumors, the mean percentage of dead cells at 6 GHz is nearly 30% higher than that at 2.45GHz, but for prolate tumors, treatment efficacy is reduced by 10% at a higher frequency. Moreover, the distance between two slots in the coaxial double slot antenna is modified based on the best treatment of prolate tumors. The findings of this study can be used to choose the optimum frequency and the best antenna design according to the shape and size of the tumor.

A review of antenna designs for percutaneous microwave ablation

“…There exist both omni-directional and directional radiation pattern approaches for delivery of the microwave energy in literature. As for omni-directional antennas, energy can be transferred into tissues in all directions around the antenna, which was usually used to eradicate tumors in a regular shape (e.g., spherical or elliptical) [21][22][23]. On the other hand, a directional antenna that affords spatial control of the energy deposition may be a better choice when tumors are in proximity to critical structures, such as blood vessels or bile ducts.…”

Applications of Microwave Energy in Medicine

“…As tumours have a higher water content than healthy tissues, the microwaves induce rapid heating via interacting with the polar water molecules within the tumour cells. Due to the microwaves ability to propagate through media, they can pass through and heat various tissues making it an applicable thermal ablation therapy for a variety of tissues [ 4 , 5 , 39 , 40 ]. Microwave ablation therapy for hepatocellular carcinoma is being viewed as a potential first line treatment for tumours on the liver surface, in which the tumour is exposed to a 2.45 GHz microwave with a wattage of 80–100 ( Figure 5 ) [ 5 , 41 ].…”

“…Due to the higher water content in cancer cells the dielectric properties of the tissue differs when exposed to microwaves [ 51 ]. Despite the nearly 40 years of research into microwave breast imaging, there are still many limitations that prevent a commercially available device that include inappropriate algorithms and sensors; however, with wider clinical trials a viable microwave imaging system may be feasible in the near future [ 39 , 40 ]. Microwave ablation has also been trialled for the treatment of breast cancer and so far has proved to be successful in thermal ablation [ 52 , 53 ].…”

“…Microwave ablation has been approved as an effective treatment for a range of cancers with promising results to be implemented for use. If the development of methods and equipment continue then this could be a cost effective, minimally invasive method of treating a variety of sized and shaped tumours [ 40 , 75 ]. Although positive, the development of such techniques is not without challenges, controlling the direction and reflection of the wave is important in all treatments to not damage healthy tissue as well as the size of the delivery antennas [ 76 ].…”

“…The antenna is most often needle-shaped but can have a variety of designs including monopole, dipole, and slotted antennas. The antenna design determines the tissue heating pattern and therefore impacts the ablation zone size and shape [ 39 , 40 ].…”