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Hyperthermia and Physics

The Role of Physics and Engineering

Physics and engineering play the same role in hyperthermia like in any other area of medical physics. Physicists and engineers are involved mainly in treatment planning, in the quality assurance of treatment and equipment, as well as in the improvement of existing and the development of new treatment modalities by applying physical principles and phenomena.

Treatment Modalities

Hyperthermia is mainly achieved through the use of ultrasound and electromagnetic energy. There are several classifications of treatment modalities according to the criteria chosen, as is shown in the following.
Physical agent used: electromagnetic radiation, ultrasound radiation, heat convection (e.g. perfusion of warm liquids).
Location of heat application: local hyperthermia (applied locally, e.g. superficial hyperthermia or thermoablation), regional hyperthermia (usually in a larger area of the body trunk) and whole-body hyperthermia.
Origin of physical agent: external (can be both superficial and deep), interstitial and intracavitary.

Hyperthermia Applicators

The diversity of applicators used in hyperthermia is surprising and the result of the different treatment modalities. In electromagnetic hyperthermia, the applicators range from small endfire antennas inserted interstitially to external arrays of radiofrequency dipoles, which are designed to offer a better control of the resulting temperature field. Arrays of applicators are also used in ultrasound hyperthermia, in focused or unfocused configurations and operating at frequencies of up to a few MHz.

Treatment Planning

Treatment planning in hyperthermia is a lot more challenging and difficult than in ionising radiotherapy. Physicists are faced with inherent limitations of the methods, as well as with non-linear phenomena. The aim of treatment planning is, in the majority of cases, to induce higher temperatures for longer periods of time at the location of malignacies in comparison to healthy tissues. This is achieved with various techniques, depending on the modality of treatment. The latest numerical methods are used in hyperthermia in order to estimate and optimise the generated temperature fields inside the human body. In fact, much of the progress made in hyperthermia has proven useful in recent years in other areas of biomedical engineering as well.

Quality Assurance

Treatment planning is closely related to the quality assurance of treatment, because any advances in it signify improvements in the control and the repeatability of treatment. Another demanding component of quality assurance is thermometry, because it gives the possibility to quantify the quality of treatment and is important for medical prognosis. The contribution of physics in this area is significant either with the application of more traditional techniques, like the use of interstitial temperature probes, or with the introduction of novel techniques like MRI thermometry.