Determination of Optimized Phase Through Correlation Between 4DCT Analysis Indices in Lung 4D SBRT.

PURPOSE/OBJECTIVE(S) Our aim is to determine maximum respiratory amplitude (RAmax) through the correlation between 4DCT analysis indices. We compare the plan quality between specific phase plans based on the determined the correlation, and consequently, we determine optimized phase in lung 4-Dimensional Stereotactic Body Radiotherapy (4D SBRT). MATERIALS/METHODS A total of 40 lung cancer patients (right sided: 20 patients, left sided: 20 patients) were enrolled in the study. Spearman correlation coefficient was used to study the relationship between 4DCT analysis indices (respiratory amplitude, volume). We regarded the relationship to establish specific phase plans (plan0-90%, plan20-70%, plan40-60%). Patients were prescribed 56 Gy for PTV and 60 Gy for ITV in 4 fractions complied with institutional protocol. VMAT (2-half arcs) plans were generated for each patient with 6 MV FFF beam of Linear accelerator. All plans were optimized that at least 95% of targets to be covered by the prescription dose. For targets, we compared plan quality between the specific phase plans using Quality of Coverage (QC), Conformity Index (CI), Homogeneity Index (HI) and Quality factor (QF). Dose constraints for OARs applied with RTOG 0915 protocol (ipsilateral, contralateral, whole lung: V5Gy 0.05). For OARs, there were significant differences with right sided (ipsilateral lung: D1500cc; 0.36i¾0.42 Gy, 0.25i¾0.27 Gy, 0.19i¾0.22 Gy, D1000cc; 1.36i¾1.58 Gy, 0.98i¾0.96 Gy, 0.77i¾0.79 Gy, P-value 0.05). CONCLUSION The study indicates that it is possible to determine the optimized phase through the correlation between 4DCT analysis indices, which can be applied it to treat in lung 4D SBRT. AUTHOR DISCLOSURE E. Heo: None. M. Kim: None. C. Park: None. K. Kim: None. J. Shim: None. H. Hwang: None. N. Lee: None. Y. Park: None. C. Kim: None. S. Lee: None.