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Abstract
Radiotherapy is an effective method for curative therapy of cancer. Various time-dose fractionation schedules have been developed for a variety of cancers of diverse histological origin. In addition to the expected positive effects of cancer cure, radiotherapy also has an influence on healthy normal tissue. In the skin these effects can be seen as acute reactions which appear during the therapy like erythema and desquamation. Late changes such as subcutaneous fibrosis and telangiectasia have an incideous progress and can be found clinically months or years after the termination of radiotherapy. The degree of these reactions is mostly scored using a qualitative descriptive scale rather than quantitative means. Since the development of the reactions provides important information on an individual's response to radiotherapy, it would be useful to have some noninvasive quantitative techniques to assess these radiation effects. Such a technique could also be valuable in the assessment of the effects of various biological response modifiers and drugs on the amelioration of late radiation-induced damage. Subcutaneous fibrosis may provide a model to develop a technique for the quantitative estimation of radiation late effects since subcutaneous fibrosis can easily be scored clinically.
In the present investigation, dielectric properties of tissues at a high radiofrequency of 300 MHz have been utilized for the evaluation of subcutaneous fibrosis. The method is based on the concept that the development of subcutaneous fibrosis decreases the total water content of skin which can be measured by dielectric methods. The skin was modeled as a two-layer electrical structure having a well-conducting surface layer with a high water content and a poorly conducting lower layer consisting of subcutaneous fat. The dielectric constant of human skin irradiated several years ago with postmastectomy radiotherapy and the skin of a Large White pig 10 weeks after single doses was measured using an open-ended coaxial line reflection method. The protein volume fraction of the investigated area was calculated and a correlation between the protein volume fraction and the clinical incidence of subcutaneous fibrosis was found. Hence it is concluded that this technique might be a useful tool in the quantitation of subcutaneous fibrosis.
