Tissue dielectric constant ratios as a method to characterize truncal lymphedema.

Truncal lymphedema is one possible complication of breast cancer treatment. It affects many women and is diagnosed based on symptoms and clinical assessment. Because changes occur late in the process, it is useful to have a quantitative assessment that is applied earlier to detect more subtle changes and quantitively assess treatment progress. Our goal was to describe a possible method to accomplish this via measurements of tissue dielectric constant (TDC). TDC was measured at lateral thorax, anterior forearm, and biceps in 120 women awaiting surgery for breast cancer. Inter-side TDC ratios were defined as values measured on the at-risk (cancer-side) lateral thorax divided by TDC values measured on contralateral thorax, forearm, and biceps. These ratios, designated as thorax-thorax, thorax-forearm, and thorax- biceps were (mean ± SD) 1.017 ± 0.121, 1.138 ± 0.223, and 1.263 ± 0.255 respectively. Corresponding truncal lymphedema thresholds were determined by adding 2.5SD to each mean yielding thresholds of 1.32, 1.70 and 1.90. For these thresholds, 99.4% of patients would have inter-side ratios less than the threshold value. Thus, from assessments in a non-lymphedematous patient-group a set of reference threshold-ratios are now available against which patients surgically treated for breast cancer may be prospectively compared.