Microwave Radiometry: Its Importance to the Detection of Cancer
Kenneth L. Carr, fellow, IEEE
(invited Paper)

Abstract - Developments in the application of microwave technology to the solution of medical, particularly the detection and treatment of cancer, for example, microwave hyperthermia has been accepted as an adjunctive produce to radiation therapy in the treatment of superficial lesions. While not as widely reported, the use of the microwave radiometry as a noninvasive, passive technique for the early detection of cancer appears very promising. Wider acceptance of these methods, however, awaits fundamental improvement in the ability to focus energy at depth in human tissue, an importance, an important and nontrivial antenna problem. Further development in the areas of antennas and antenna arrays is required if microwave technology is to provide a practical solution to the detection and treatment of cancer. This paper discusses developments in the medical users of microwave radiometry, particularly in relation to the detection of cancer, as well as significance of and progress in related antenna technology.

Introduction

American Cancer Statistics [1] indicate that in 1981 there was 30000 estimated deaths, with an estimated 111000 new cases, as a result of breast cancer. Over the 50-year period between 1930 and 1980, there has been no appreciable change in death rate and tragically, approximately one in every 11 women in the USA will experience breast cancer during her lifetime. In 1987 there were 40000 estimated deaths, with an estimated 119000 new cases. It is an established observation that survival depends upon pathologic stage of disease at the time of treatment. Table 1 indicates the dramatic increase in survival as a result of early detection [2]. (In 1930, for example, cancer of the uterus was the leading cause of death due to cancer in women in the USA. Cancer of the uterus has declined steadily since that time due in part to improved hygiene, but primarily due to the development of an early detection technique [i.e. the Papanicolaou test]. Today, 95 present of all breast tumors are found by physical examination by either the patient or the examining physician. The result is that long before a breast tumor can be detected by present technology, nodal involvement may occur [3], [4].

Fig. 1 illustrates the long preclinical existence of breast carcinoma [5], [6]. The curve was generated by measuring the growth over a period of and assuming the growth rate to be constant - in this case, using a lamer Ť doubling timeť of 100 days and extrapolating to establish the time of its inception. Accordingly, the visible or clinical phase (i.e. when a tumor diameter of 1 cm is achieved) occurs on average of 8 years after inception. Unfortunately, the average tumor diameter when first detected and diagnosed as malignant is approximately 2 to 2.5 cm and typically not a localized disease.

While cancer cells can be released at any time during tumor growth, the larger the tumor the large the number of cells released. According to Gullino [7], ŤWe know that the great majority of circulating pcoplastic cells are destroyed, bat the higher their number the higher is the frequency of metastasis. On this ground, early diagnosis and removal of the primary tumor is essential.

Fig. 1 Dubbing time tumor in relation to clinical phase

Mammography will remain the standard against which new screening techniques will be compared. According to Lundgren [6], however, the average diameters detected by mammography was 75 percent of the average diameter detected by palpation. This is not adequate lead time. (The time assumed to be gained in the diagnosis of breast cancer by screening a population of apparently well women is known as the lead time.)

We discuss in the following microwave thermography, or, more correctly, radiometry, with is defined as the measurement of natural electromagnetic radiation or emission from the body at microwave frequencies to allow the detection and diagnosis of pathologic conditions in which there are disease related temperature differentials. The application of radiometry has, for the most part, been directed at the early detection and diagnosis of breast cancer.

Present detection techniques other than radiometry require that the tumor have mass and contrast with respect to the surrounding tissue (i.e., palpation physical examination, mammography, ultrasonography and diaphonography). Despite the live-saving potential of mammography and the progress made in less radical forms of breast cancer surgery, only about 5 percent of women over the age of 50 undergo annual mammography. Only about one third of these women, quality for mammography under the American college of Radiology and the American Cancer Society guidelines, had even one examination. The factors contributing to this low screening rate are complex and diverse, and are not completely understood. Due to late detection, approximately 85 percent of all determinations of breast disease result in extensive surgical procedures (i.e., discovery of a tumor usually means loss of breast and with it a negative attitude toward detection). Early detection could lead to a more conservative treatment and a positive attitude toward detection. Suspicious results found by screening using microwave radiometry could then referred for mammography.

Radiometric techniques represent a passive, noninvasive, noninonizing procedure determining thermal activity rather than mass that, when used in conjunction with one or of the other methods, could provide early detection. The determination of thermal activity is a measurement of tumor activity, or growth rate [8], providing date beyond the physical parameters (i.e., size and depth determined by mammography).

References

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