Sensitivity and repeatability of diffuse optical tomography: towards breast cancer neoadjuvant treatment monitoring

It is expected that the optical signatures of physiological changes are biomarkers reacting faster to breast tumor evolution than structural changes, meaning that diffuse optical tomography (DOT) could be a promising modality for monitoring and detecting early changes of the lesion during neoadjuvant treatment. Numerous publications as well as our preliminary results revealed that the heterogeneity inside the breast and the variability within the population are challenging for such application. Moreover the sensitivity of the breast physiology to the external pressure applied during data acquisition is adding a significant variance to the process. In the present study we evaluate key factors that could make neoadjuvant treatment monitoring, using DOT, successfully: 1) sensitivity-the clue for earlier detection; 2) repeatability-minimizing the impact of the artificially induced variance (related with pressure, angle of the view, etc.); 3) accurate co-localization of the ROI within the sequential measurements performed during the neoadjuvant treatment. Non-clinical and clinical studies were performed using a multi-wavelength time-domain platform, with transmission detection configuration, and 3D images of optical and physiological properties were generated using diffuse propagation approximation. The results of non-clinical studies show that the sensitivity of the system allows detection and quantification of absorption changes equivalent to less than 1 micromole of blood. Clinical studies, involving more than 40 patients, revealed that with the appropriate precautions during patient positioning and compression adjustment, the repeatability of the results is very good and the similarities between the two breasts are high suggesting that the contra-lateral breast could be used as a reliable reference for DOT as well.