SAN ANTONIO—Optical tomography with ultrasound localization has the potential to monitor tumor vascular changes during neoadjuvant chemotherapy, according to a pilot study in which the modality was able to distinguish between responders and nonresponders, and even between complete and partial pathologic responses. Susan Tannenbaum, MD, of the University of Connecticut, Farmington, described the approach at the 2007 San Antonio Breast Cancer Symposium (abstract 45).
Optical tomography uses diffused light in the near-infrared (NIR) spectrum for imaging tissue. As light passes through the body, a quantifiable portion of it is absorbed by blood vessels. Tumors have higher microvessel density or higher blood volumes than nonmalignant tissues, and total hemoglobin (tHb) concentration, as measured by NIR, is directly related to tumor vascular content. Prior studies by the University of Connecticut and Hartford Hospital researchers and physicians have shown that tHb concentration is much higher in cancerous than in nonmalignant breast masses.
“Due to the intense light scatter that occurs when NIR travels through tissue, three-dimensional image localization is poor and quantification of light is imprecise,” Dr. Tannenbaum said. To optimize light localization and quantification, co-author Quing Zhu, PhD, professor of bioengineering, and colleagues coupled NIR with ultrasound (US) to produce an NIR-US imaging modality that simultaneously acquires US images and optical data via a handheld probe
“This volumetric data is then reconstructed tomographically in 5 mm cuts from skin down to chest wall,” Dr. Tannenbaum said. Each slice shows the volume and distribution of tHb concentration (the tHb map).
Patients with stable disease tend to show virtually no difference in tHb maps before and after treatment, she said. Complete pathological responders show marked reductions in tHb maps after treatment. And partial responders demonstrate some degree of volume loss and reduction in tHb concentration, “although it is less pronounced than in the complete responders,” she explained.
The investigators then quantitated these changes in tHb during treatment for each patient in the study to determine whether these absolute changes might reflect pathologic response groups.
To quantify tHb content, they calculated the blood volume index (BVI) (total volume of tHb within the tHb map × average tHb). Then, to measure vascular changes during treatment, they used the percent BVI (PBVI) at any cycle, compared to the pretreatment BVI.