SU‐E‐J‐271: Correlation of CT Number Change with Radiation Treatment Response for Pancreatic Cancer

Purpose: It has been reported recently that radiation can induce CT number (CTN) change during radiation therapy (RT) delivery. In the effort to explore whether CTN can be used to assess RT response, we analyze the relationship between the pathological treatment response (PTR) and the changes of CTN, MRI, and PET before and after the neoadjuvant chemoradiation (nCR) for pancreatic adenocarcinoma. Methods: The preand post‐nCR CT, MRI, and PET data for a total of 8 patients with resectable, or borderline resectable pancreatic head adenocarcinoma treated with nCR were retrospectively analyzed. Radiographic characteristics were correlated to PTR data. The histograms, means and standard derivations (SD) of the CTNs in pancreatic head (CTNPH), the GTV defined by ADC (CTNGTV), and the rest of pancreatic head (CTNPH‐CTNGTV) were compared. Changes before and after nCR were correlated with the corresponding changes of ADC, lean body mass normalized SUV (SUVlb), and PTR using Pearson’ s correlation coefficient test. Results: The average mean and SD in CTPH for all the patients analyzed were higher in post‐nCR (53.17 ± 31.05 HU) compared to those at pre‐nCR (28.09 ± 4.253 HU). The CTNGTV were generally higher than CTNPH and CTNPH‐CTNGTV, though the differences were not significant. The post‐nCR changes of mean CTN, ADC, and SUVlb values in pancreatic head were correlated with PTR (R=0.3273/P=0.5357, R=−0.5455/P