A New CBCT Image Analysis for the Evaluation of Tumor Response to Lung SBRT
Presentations
MO-H345-IePD-F6-4 (Monday, 7/11/2022) 3:45 PM - 4:15 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 6
Purpose: To determine if the radiographic signs of tumors described by CNR, Size and CT number in CBCT images can be used for the evaluation of tumor response to lung SBRT.
Methods: The cone-beam CT (CBCT) images for lung SBRT patients were taken for each treatment and exported to the Varian Eclipse treatment planning system. The CBCT image taken for the first and last fractions were analyzed using the ImageJ and Eclipse measurement tool. The gap between the first and last treatment was at least 7 days. The contrast-to-noise ratio (CNR) and size of tumor were measured by ImageJ. The Hounsfield unit (HU) or CT number was determined on the Eclipse treatment planning system. The ratios of tumor CNR, size, and HU (RC, RS, RH) between the fifth and first fractions were calculated. The product of the three rations (R) was used to evaluate the tumor response. Meanwhile, tumor response was also assessed by a radiologist using the same CBCT images. The radiological assessment was used as the reference to evaluate the tumor response based on R values using statistical analysis.
Results: Thirty lung cancer patients who received 5-fraction SBRT treatment were included in this study. Tumor response to SBRT was defined as Response (R<1.0) and Progression (R>=1.0). The results derived from R values achieved the specificity of 86.4% and the sensitivity of 87.5%. The respond prediction was 95% and the progression prediction was 70%.
Conclusion: The results of the study show that change in CNR, size and HU between the first and last fraction was correlated with tumor response. This indicates that the use of radiographic signs quantified by R can be a viable method for the evaluation of tumor response to SBRT.
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