Room: Exhibit Hall | Forum 2
Purpose: To investigate feature variability of longitudinal cone-beam CT radiomics for 3 different fractionation schemes and a time-point during treatment indicative of early treatment response.
Methods: Of 72 NSCLC patients treated with lung SBRT, 18 received 15-18Gy times 3 fractions; 36 received 12-12.5Gy times 4 fractions; 18 received 8-10Gy times 5 fractions. We studied 7 sets of CBCT images from the same treatment fraction as a â€˜test-retestâ€™ baseline to study the additional daily CBCT images. Fifty-five gray level intensity and textural features were extracted from each CBCT image. Test-retest images were used to determine the smallest detectable change (C=1.96*SD) indicating significant variation with a 95% confidence level. Here, the significance of feature variation depended on the choice of a minimum number of patients for which a feature changed more than â€˜Câ€™. Analysis of which features change at which moment during treatment with different fractionation schemes was used to investigate a time-point indicative of early tumor response.
Results: Following lung SBRT, 30 features changed significantly for at least 10% of all patients. For patients treated with 3 fractions, 49 features changed at Fraction 2, and 49 at Fraction 3; there was 100% overlap between features at both fractions. For patients treated with 4 fractions, 45, 45, and 48 features changed at Fraction 2-4 respectively; there was 92% overlap between features at Fraction 2 and the remaining fractions. For patients treated with 5 fractions, 12, 18, 14, and 25 features changed at Fraction 2-5; there was 36%, 48%, and 48% overlap between features at Fraction 2-4 and the remaining fractions respectively.
Conclusion: Significant changes in gray level radiomic features were observed over the course of lung SBRT. Higher fractional dose corresponded to a larger number of variable features and high overlap of variable features at an earlier time-point.
Funding Support, Disclosures, and Conflict of Interest: This study is partially supported by a Varian research grant.