Near Infrared Imaging Using US Localization To Assess Response to Neoadjuvant Chemotherapy.

Abstract

Abstract Background: Pilot data obtained from a novel ultrasound (US)-guided diffusive-wave optical tomography in the near infrared (NIR) spectrum showed that it is feasible to use this technique to monitor vascular changes within breast tumors during neoadjuvant chemotherapy. These changes correlated well to tumor pathologic response. The earlier study was performed at a single hospital with a smaller patient pool and the tumor vascular assessment was made at a period of two treatment cycles. The objectives of this study are: (i) to validate the initial findings with a larger patient pool, and (ii) to assess vascular changes at every treatment cycle and to correlate early vascular changes with the tumor pathological response.Materials and Methods: 13 patients who underwent neoadjuvant treatment were recruited from two hospitals from December 2007 to May 2009 and their tumor vascular content was assessed with a combined imager consisting of a commercially available US system coupled to a NIR imager (NIR/US). Patients were imaged before their treatment, at the end of every treatment cycle and before their definitive surgery. The co-registered US was used to localize the tumor and to guide the NIR imaging reconstruction, and the NIR imager was used to map the tumor vascular distribution which was assessed based on a percentage total hemoglobin (%tHb) concentration normalized to the pre-treatment level. Of the 13 patients, 12 patients had contrast enhanced MRI before treatment and prior to surgery. The NIR results were compared with MRI findings. At treatment completion, pathological assessment revealed three response groups: complete or near-complete responders (A), partial responders (B), and non-responders (C).Results: There were four complete or near-complete responders, five partial responders, and four non-responders. The mean %tHbs of groups of A, B and C at the treatment completion were 38%±7.0%, 57.3%±5.7%, and 91.0%±10.1%, respectively (differences statistically significant, p<0.05). At the end of cycle one, the %tHb of group A showed no noticeable difference than that of partial and non-responder groups, however, the %tHb at the end of cycle two or three of group A was significantly lower than that of partial and non-responder groups. Figure 1 shows an example of a complete responder imaged before the treatment and at the end of cycle two.All complete or near-complete responders showed rapid reduction in %tHb at the end of cycle two or three; while all non-responders showed no change or small change in %tHb throughout the treatment. On average, partial responders showed changes in between. Both NIR/US and MRI were equally effective in distinguishing different response groups in this study.Discussion: Our findings indicate that NIR can be used during neoadjuvant chemotherapy to repeatedly monitor tumor vascular changes. NIR/US may also assess early pathological response during treatment. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5016.