Treatment Response Assessment Using Daily Dual-Energy CT during Pre-Operative Radiation Therapy for Early-Stage Breast Cancer

Abstract

<h3>Purpose/Objective(s)</h3> We have previously reported that the low energy mono-energetic images (MEI) derived from dual-energy CT (DECT) can amplify the detection of radiation-induced changes in tissue. This work aims to investigate the use of low energy MEI derived from daily DECT to assess tumor response during radiation therapy (RT) of early-stage breast cancer. <h3>Materials/Methods</h3> Daily DECT data acquired during routine CT-guided RT delivery for 35 early-stage breast cancer patients enrolled in an institutional prospective pre-operative accelerated partial breast irradiation trial, along with tumor pathological data collected from the biopsy before RT and the excised tissue from the surgery post RT, were analyzed. All patients were treated with 30 Gy in 5 fractions in two weeks. The DECTs were acquired immediately before the fractional dose delivery using an in-room CT scanner equipped with a sequential DE protocol. MEI images across a range of x-ray energies were reconstructed using an image-based material decomposition. Fractional changes in mean CT number (mCTN) in gross tumor volume (GTV) on MEIs were extracted and the changes from the first to the last fraction were correlated to the tumor cellularity changes from the pathological data collected before and after RT using the Student's T-Test. As a control, the mCTN changes on MEIs in a region far from irradiated volumes were calculated. The results from the MEI data were compared to those obtained from the standard 120 kVp CTs of the same subjects. <h3>Results</h3> The data from 20 out of 35 patients were found to be suitable for this analysis. The greatest enhancement in GTV mCTN change was observed for MEI at 40 keV, the lowest available energy. The average change in GTV mCTN between the first and last fractions of treatments was 2.9 times larger for 40 keV MEIs than that for the standard 120 kVp CTs. For 11 out of the 20 patients, the GTV mCTN changes were greater than 15 HU on the 40 keV MEI and their average change in cellularity was 36.5 ± 10.3%. For the remaining 9 patients, the GTV mCTN changes were less than 15 HU on the 40 keV MEI and the average change in cellularity was 14.4 ± 9.8%. The correlation between change in GTV mCTN and change in cellularity was found to be significant (p=0.02). The average mCTN change in the control region was of 0.2 ± 2.0 HU on the 40 keV for all 20 patients. <h3>Conclusion</h3> Tumor pathological response for early-stage breast cancer treated with pre-operative accelerated partial breast irradiation can be predicted by the change of quantitative features, such as mean CT number, on low energy MEI derived from DECT acquired during the radiation treatment. Compared to the standard CT, the low energy MEIs substantially amplify the changes of mCTN, enhancing the viability of using quantitative CT features as a biomarker for early RT response assessment.