Ultrasound scattering statistics predicts the result of neoadjuvant chemotherapy of breast tumors at an early stage of treatment

Neoadjuvant therapy (NAC) for breast tumors involves administering chemotherapeutic agents to the patient before a tumor resection surgery. An assessment of a cancer response to the medicine is an important aspect of the therapy. It is necessary to decide whether to continue the treatment, change the drug or refer the patient to a surgery to remove the tumor. Quantitative Ultrasound (QUS) techniques can help in assessing the therapy and the decision-making process. These techniques provide quantitative parameters related to a tissue structure, thus changes in the parameters values can be related to changes in the tissue. The aim of this study was to assess the tumor response to the therapy, basing on statistical parameters of backscattered ultrasound signals. The data were acquired from 34 tumors during NAC therapy. First measurement (a baseline) took place before a start of the therapy, and next measurements were carried out about a week after each NAC administration. At the end of the treatment, the tumors were excised, examined histopathologically, and a percentage of residual malignant cells (RMC) in tumor tissue was estimated. As a part of the data analysis, an experienced physician specified a tumor area (Region of Interest -ROI) on each ultrasound image. Then, two statistical parameters of a signal amplitude probability distribution within the ROI was estimated. The first was the shape parameter of the homodyned k distribution, and the second was the Kullback-Leibler divergence between amplitude distributions estimated from the baseline and succesive masurements. These parameters were used to classify tumors during therapy as "responding" or "not responding" to treatment, assuming that non-responding tumors have an RMC > 75%. Results suggest that QUS parameters obtained from amplitude statistics can be useful in the NAC monitoring and provide additional information to physicians.