Investigation of thermal effect by focused ultrasound in cancer treatment

Every year, millions of people are subjected to cancer around the world and more than half of the patients die from it. In almost all countries, cancer ranks among the most common cause of death. As elderly people are most susceptible to cancer and population aging continues in many countries, cancer will remain a major health problem around the globe [1]. An important approach in the fight against cancer is the discovery of novel techniques for diagnosis and treatment [2]-[5]. Accurate diagnosis and treatment methods will empower the therapy for patient care. High intensity focused ultrasound (HIFU) is a novel technique in cancer treatment. An HIFU transducer coupled to an electronic supply system generates high frequency sound waves and delivers a strong beam to a specific part of cancer tissue [6], [7]. Some cells die when the high intensity ultrasound beam is focused directly onto them. This type of treatment uses only sound waves to kill the cancer cells and it does not result in significant side effects as observed with other types of cancer treatment techniques such as ionizing radiation. Other heating techniques such as laser or microwave therapy have some disadvantages compared to the HIFU technique. When a laser is directed to tissue, it effectively burns throughout its path, and microwaves are harmful for the human body. The basic principle of focused ultrasound is analogous to using a magnifying glass to focus sunlight. Focusing the ultrasound beam generates enough heat for burning. Focusing can be done geometrically, for example with a lens or with a spherically curved transducer, or electronically, by adjusting the relative phases of elements in an array of transducers. Ultrasound beams pass through tissue with no effect except at the focal point where the beams converge, where they produce high energy as seen in Fig. 1. The energy can have both thermal and mechanical effects. HIFU is currently used in treatment in certain situations for some types of cancers such as prostate, kidney, or liver cancers. The HIFU technique in cancer treatment can be used individually or with other techniques like ionizing radiation. As this treatment results in critical necrosis in the part of tissue, it must be well investigated by using sophisticated systems in light of available metrological tools.