PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) is considered as an alternative treatment for medically inoperable patients with early-stage non-small cell lung cancer (NSCLC); however, 10–15% of these patients develop local recurrence after high-dose SBRT. Recently, dual-energy computed tomography (DECT) was introduced, and material densities (iodine, water, etc.) become measurable. Reduction in iodine density, suggesting a decrease in blood flow, may reflect hypoxic cell population in the tumor, and the hypoxic microenvironment plays a critical role in the development and progression of tumors. In contrast, the water density is presumed to reflect the cell density and necrosis of cancer cells, however, the study of water density regarding NSCLC is insufficient. The purpose of this study was to investigate impact to prognostic of water and iodine density assessed by DECT for NSCLC treated with SBRT.
Materials/Methods: From March 2011 to December 2017, 153 medically inoperable patients with primary NSCLC underwent DECT prior to SBRT of a total isocentric dose of 50–60 Gy in 5–6 fractions. The median patient age was 78 years (range, 52–91 years). DECT was taken for pretreatment evaluation. Regions-of-interest was set at the maximum cross-sectional diameter of the tumor, and average values of water and iodine density obtained by dedicated imaging software were evaluated with regard to overall survival (OS) rates and local control (LC) rates using Kaplan–Meier method. Cox proportional hazards model was applied for multivariate analysis.
Results: The median values of the average water and iodine density were 968.3 mg/cm3 (range, 191.9–1036.1 mg/cm3) and 1.86 mg/cm3 (range, 0.12–5.52 mg/cm3), respectively. There was no significant correlation between water density and iodine density. The median follow-up period was 24.6 months (range, 1.5–82.8 months). The 2-year OS rates for the water density in high and low groups were 82.0% and 89.2% (P = 0.011); the corresponding rates for the iodine density in high and low groups were 92.3% and 79.3% (P = 0.019), respectively. The 2-year LC rates for tumors according to the water density in high and low groups were 87.4% and 94.9% (P = 0.197); the corresponding rates according to the iodine density in high and low groups were 98.0% and 82.5% (P = 0.011), respectively. In multivariate analysis for OS, iodine and water density were selected as prognostic factors. In multivariate analysis for LC, iodine density was selected as prognostic factor.
Conclusion: The reduction of the water density had a significant positive impact on overall survival, and the reduction of the iodine density had a significant negative impact on overall survival and local control. Our preliminary results indicated that the water and iodine density assessed by DECT might be a useful, noninvasive and quantitative assessment as a prognostic indicator for NSCLC treated by SBRT. Further study is needed to confirm these results in larger population with longer follow-up.
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