SU‐F‐R‐54: CT‐Texture Based Early Tumor Treatment Response Assessment During Radiation Therapy Delivery: Small Cell Versus Non‐Small Cell Lung Cancers

Abstract

Purpose:Tumor treatment response may potentially be assessed during radiation therapy (RT) by analyzing changes in CT‐textures. We investigated the different early RT‐responses between small cell (SCLC) and non‐small cell lung cancer (NSCLC) as assessed by CT‐texture.Methods:Daily diagnostic‐quality CT acquired during routine CT‐guided RT using a CT‐on‐Rails for 13‐NSCLC and 5‐SCLC patients were analyzed. These patient had ages ranging from 45–78 and 38–63 years, respectively, for NSCLC and SCLC groups, and tumor‐stages ranging from T2‐T4, and were treated with either RT or chemotherapy and RT with 45–66Gy/ 20–34 fractions. Gross‐tumor volume (GTV) contour was generated on each daily CT by populating GTV contour from simulation to daily CTs with manual editing if necessary. CT‐texture parameters, such as Hounsfield Unit (HU) histogram, mean HU, skewness, kurtosis, entropy, and short‐run high‐gray level emphasis (SRHGLE), were calculated in GTV from each daily CT‐set using an in house software tool. Difference in changes of these texture parameters during RT between NSCLC and SCLC was analyzed and compared with GTV volume changes.Results:Radiation‐induced changes in CT‐texture were different between SCLC and NSCLC. Average changes from first to the last fractions for NSCLC and SCLC in GTV were 28±10(12–44) and 30±15(11–47) HU (mean HU reduction), 12.7% and 18.3% (entropy), 50% and 55% (SRHGLE), 19% and 22% (kurtosis), and 5.2% and 22% (skewness), respectively. Good correlation in kurtosis changes and GTV was seen (R2=0.8923) for SCLC, but not for NSCLC (R2=0.4748). SCLC had better correlations between GTV volume reduction and entropy (SCLC R2=0.847; NSCLC R2=0.6485), skewness (SCLC R2=0.935; NSCLC R2=0.7666), or SRHGLE (SCLC R2=0.9619; NSCLC R2=0.787).Conclusion:NSCLC and SCLC exhibited different early RT‐responses as assessed by CT‐texture changes during RT‐delivery. The observed larger changes in various CT‐texture parameters for SCLC indicate that SCLC may respond to RT more rapid than NSCLC.