Enhancement Of Ct Based Treatment Response Detection For Breast Cancer Using Dual-Energy Ct

Radiation can induce changes in CT textures during radiation therapy (RT) and the changes can potentially be used to assess RT response for breast cancer. These changes will be amplified if the X-Ray energy is reduced due to the rapid growth of the photoelectric effect below 100 keV. The purpose of this study is to investigate the use of low energy mono-energetic images (MEI) obtained from dual energy (DE) CT to enhance the detection of radiation induced changes during RT delivery. DECT data was analyzed for 10 breast cancer patients treated with 30 Gy in 5 fractions delivered on non-consecutive days on a phase 2 study of pre-operative accelerated partial breast irradiation (APBI) during routine CT-guided RT delivery using an in-room CT scanner equipped with a sequential DE protocol. Conventional CT (120 kVp) and DECT (with a sequential protocol) were acquired in alternate days. MEI images across a range of energies were reconstructed using an image-based material decomposition. Changes in quantitative features including mean CT number (mCTN) and first order textures (skewness, kurtosis, entropy, variance) were extracted. The results from the MEI data were compared to those obtained from the standard 120 kVp CTs of the same subjects. Correlation between the changes of selected CT features and the cellularity data obtained from the pathologic analysis of the surgical specimen after the APBI was assessed. Radiation can induce substantial changes in the textures of the daily CTs. As measured from MEI, mCTN and entropy can be changed by up to 35 HU and 17%, respectively, during RT delivery. Compared to those based on the conventional CT, these changes were amplified by the low energy MEI. The average change in mCTN between the first and last week of treatment was 2.0 times larger for 40 keV MEI than that for average change in mCTN for the 120 kVp CTs. For a representative patient the kurtosis decreased by a factor of 4.6 during RT delivery as measured on 40 keV MEI, 3.8 times larger than that from 120 kVp CTs. The excised tissue of patients that experienced a change in mCTN from 40 keV MEI of greater than 10 HU had an average cellularity of 2.8 ± 2.4% whereas for those for whom the change in mCTN was less than 10 had an average cellularity of 42.5 ± 22%. A significant correlation was observed between change in mCTN at 40 keV and low (≤10%) cellularity of excised tissue using the Student’s t-Test (p=0.007). Using the same test the correlation between change in mCTN at 120 kVp and low cellularity of excised tissue was not found to be significant (p=0.055). Radiation-induced changes in CT textures during RT delivery for breast cancer are amplified if they are measured from MEI of DECT, enhancing the viability of using CT texture changes as a biomarker for early RT response assessment while patients are receiving treatment.