Background <p>Two-dimensional mapping based on reflectance measurements is a promising approach for evaluating the characteristics of breast cancer and its response to chemotherapy. However, three-dimensional imaging should enable extraction of more accurate values and distributions of the parameters, potentially increasing the validity of the assessment. Therefore, we have been developing reflectance diffuse optical tomography (RDOT) for three-dimensional imaging of breast cancer using time-domain reflectance measurements.</p> Methods <p>We performed RDOT imaging on 64 patients with breast cancer and acquired three-dimensional images of total hemoglobin concentration (tHb) and tissue oxygen saturation (StO₂) at the lesion and a symmetrical area in the normal breast. The correlation between tHb and the skin-to-chest wall distance was investigated to evaluate the effect of the chest wall. We also examined correlations of tHb with tumor depth and tumor thickness. In addition, we measured patients with breast cancer before and after they underwent neoadjuvant chemotherapy and compared the results.</p> Results <p>The tHb value increased in both cancerous and normal breasts as the skin-to-chest wall distance decreased. Cancerous breasts showed higher tHb and lower StO₂ than normal breasts. tHb showed a negative correlation with tumor depth and a positive correlation with tumor thickness. Long-term monitoring of lesions during chemotherapy demonstrated that tHb decreased as the tumor size reduced with chemotherapy.</p> Conclusions <p>We confirm that the RDOT has potential for a novel examination method with no pain and no radiation exposure; however, the reconstructed image is still affected by chest wall, tumor size, and tumor depth.</p>