3449 - Analysis of Dual-Energy CT (DECT) Parameters in Patients with Stage I Non-Small Cell Lung Cancer Treated with Stereotactic Ablative Body Radiation (SABR) in a Prospective Study

W. C. Hsu¹, S. Mao², E. Vonderhaar Meister², P. B. Illei³, R. K. Hales⁴, C. Hu⁵, J. R. Brahmer⁶, P. Forde⁷, J. Naidoo⁸, V. Anagnostou⁹, K. Smith¹⁰, C. T. Lin¹¹, and R. Voong⁴; ¹Johns Hopkins University S, Baltimore, MD, ²Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, ³Department of Pathology Johns Hopkins University, Baltimore, MD, ⁴Johns Hopkins Radiation Oncology Kimmel Cancer Center, Baltimore, MD, ⁵Division of Quantitative Sciences, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, ⁶Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, ⁷Johns Hopkins University School of Medicine, Baltimore, MD, ⁸Sidney Kimmel Comprehensive Cancer Center and Bloomberg-Kimmel Institute for Cancer Immunotherapy at John Hopkins University, Baltimore, MD, ⁹Bloomberg-Kimmel Institute for Cancer Immunotherapy, Johns Hopkins,, Baltimore, MD, ¹⁰Department of Oncology Johns Hopkins University, Baltimore, MD, ¹¹Department of Radiology and Radiological Science, Johns Hopkins School of Medicine, Baltimore, MD

Purpose/Objective(s): DECT scans measure intratumoral iodine concentration, which provides valuable insights into the tumor environment including blood supply and metabolic activity. The purpose of this study is to examine the short-term changes in DECT parameters patients with stage I non-small cell lung cancer (NSCLC) after SABR therapy. Materials/

Methods: Patients =18 years with stage I NSCLC were consented and enrolled in an IRB-approved prospective study. Patients received SABR (48Gy/4 fractions or 50Gy/5 fractions) and had chest DECT scans before and 5-7 days following SABR. Color iodine maps and atomic number maps were generated utilizing a post-processing algorithm (Siemens Syngo.via). Two blinded radiologists reviewed scans and quantified DECT parameters (iodine concentration (IC) and atomic numbers (Zeff)). Normalized iodine concentration (NIC) was calculated to decrease hemodynamic impact by dividing the IC of the tumor by the IC of the aorta. Descriptive statistical analysis compared the parameters before and after SABR. The difference between values was calculated as the post-SABR value minus the pre-SABR value.
Results: Six patients enrolled, with a median age of 75 years (66 - 83) and a median tumor size of 1.9 cm (0.84 - 3.0). Adenocarcinoma was the predominant histopathology (n=4). At a median follow-up of 40 months, 83% (5/6) patients had tumor control after SABR alone. One patient experienced locoregional recurrence 13 months post-SABR. In comparing IC from color iodine maps pre- and post-SABR, the mean IC was 1.95 and 2.37, respectively. Four patients showed increase in IC, with the patient who later developed recurrence displaying the largest increase (pre-SABR 2.5 ng/ml, post-SABR 3.6 ng/ml, difference 1.1 ng/ml). NIC analysis followed a similar pattern of increase in mean values post-SABR (pre-SABR: 0.35, post-SABR: 0.39). In atomic number maps, the mean Zeff was 8.60 pre-SABR and 8.56 post-SABR. Half the patients showed an increase in Zeff after SABR, and the patient with recurrence displayed the highest Zeff value after SABR (9.23).
Conclusion: These data provide evidence that SABR induces acute macroscopic changes within stage I NSCLC tumors, affecting their composition and vascularity. Our data show the greatest changes in IC, NIC and Zeff values in the patient who clinically recurred over a year following the SABR. This suggests DECT parameters may provide a noninvasive assessment of immediate clinical response to SABR and provide a foundation from which additional studies may be built to assess the extent to which DECT can be used a as marker of post-SABR clinical response or recurrence