Ultrasonic hyperthermia

Abstract

At the beginning, ultrasonics in the field of medicine was oriented to applications in therapy rather than diagnosis, and its heating and dissociation effects were used on biological tissues. We call ultrasonic therapy to the use of high-intensity ultrasounds in order to induce changes in the state of the tissue by means of their thermal and other effects. Hyperthermia is a relatively new therapy cancer treatment. Its effects are obtained by increasing the temperature range in the tumor target up to 42-45 °C. When the rate of body temperature increment exceeds the ability of the regulation system to dissipate the heat, the cells die. The cells of a solid cancerous tumor are even more sensitive to heat than normal cells. For this therapy to be effective, the temperature increase must be maintained between 30 to 60 minutes per treatment, and it is usually preceded or followed by conventional oncology treatments such as radiotherapy or chemotherapy. The clinical results obtained by several clinical researchers are encouraging for the treatment of some kinds of tumors. The heating of cells induces conformational changes of certain proteins that depend on pH values. These conformational changes lead to alteration of multimolecular structures like cytoskeleton, membranes and also some structures in the cell nucleus. Metabolic changes like the increase of metabolic rates, lactate rates and the decrease of pH are also induced by heat. These conformational and metabolic changes lead to alteration of the microenvironment in tumors and has an impact on cellular death induced by heat [1]. The heating of cancerous tissues can be accomplished by several means, like electromagnetic and ultrasonic radiation among others. Electromagnetic radiation can be used to treat small tumors located in relatively homogeneous tissue regions such as breast, brain, and perhaps the soft tissue regions of the head and neck; yet, some hyperthermia treatments may bebest executed by using ultrasound radiation. However, it is important to mention that the areas where ultrasound cannot be successfully applied are those where bone or air regions block its path [1]. Some of the advantages of using ultrasound include the feasibility of constructing applicators of almost any shape and size and the good penetration of ultrasound at frequencies where the wavelengths are on the order of millimeters. The small wavelengths allow beams to be focused and controlled. Hyperthermia systems need highly accurate control of the changes in the focalization of the field, which result from the changes in the properties of tissue after heating, as well as of the temperature increase in the zone treated. It is easier to focus energy with ultrasound than with other hyperthermia techniques, which allows that tumors located deeply within the body can be treated. The main problem, as mentioned before, is the accuracy in the method of directing, measuring and controlling the heat. © Springer-Verlag Berlin Heidelberg 2008.