Room: Track 2
During radiation therapy (RT), patient hematocrit (HCT) level can change. This work aims to investigate whether quantitative CT acquired during RT can be used as an image biomarker to measure the HCT change.
Daily diagnostic-quality CTs acquired during routine CT-guided RT using a CT-on-rails for 17 patients including 4 cervical (CC), 8 pancreatic (PC), and 5 head and neck (HNC) cancers, along with their complete blood count (CBC) data collected weekly throughout the treatment course, were analyzed. The CT on the same day of CBC was selected, resulting in on average 6 CT-CBC data pairs for each patient. On the selected CT set, veins were consistently contoured to obtain the distributions of blood CT numbers (CTN) in the veins. The correlation between the changes of HCT and blood CTN was analyzed for each patient. The slope and intercept were used to calculate the intrinsic CTNs of blood cells and plasma.
On average, HCT was reduced by 6.9% and the blood CTN was decreased accordingly by 4.9 HU during the entire RT course. The correlations between the changes of CTN and HCT were 0.86±0.06 for CC, 0.84±0.20 for PC, and 0.80±0.20 for HNC. The calculated CTNs of blood cell and plasma are 80.4±4.2 HU and 18.1±5.7 for CC, 79.1±10.4 HU and 12.4±6.1 HU for PC, and 76.1±13.9 HU and 20.6±11.1 for HNC, respectively.
Blood CTN and HCT and their changes during RT are strongly correlated. This correlation and calculated cells and plasma CTNs are independent of body sites. For a specific patient, the CTNs of blood cells and plasma can deviate with a wide range, suggesting individual histology characterization of patients. With further studies based on larger datasets, the CT routinely acquired during RT may be developed as a free image biomarker for HCT change during RT.