Baseline shift corrections towards the heart: External validation of the impact on survival in early-stage NSCLC patients

Purpose To externally validate Johnson-Hart et al. findings: the association of tumor baseline shifts towards the heart with overall survival(OS) in SBRT for NSCLC. Further analysis included investigating the presence of interfractional heart baseline shifts and the association of OS with heart dose change during treatment. Methods Data from 416 SBRT early-stage NSCLC patients was collected. Pearson’s correlations(PCCs) between clinical variables and treatment-averaged tumor shifts towards/away from the heart were explored. Validation of published multivariable Cox model was performed. PCC between heart and tumor baseline shifts was analyzed. Dose accumulation was performed following daily CBCT-to-pCT deformable registration. Maximum heart dose(D0) was computed for planned and accumulated doses. Differences in OS according to shifts towards/away from the heart or D0 increase/decrease were analyzed. Significant D0 differences between patients with D0 increase/decrease and different tumor locations were explored. Results Tumor shifts towards/away from the heart showed no significant association with OS(p = 0.91). Distance between PTV and heart correlated significantly(PCC = 0.18) with shifts to the heart. Cox model did not validate in our cohort. Heart presented baseline shifts positively correlated with tumor baseline shifts in all three directions(PCC ≥ 0.38;p < 0.001). Counterintuitively, patients experiencing increased D0 during treatment showed significantly better OS(p = 0.0077). Upper-lobe tumor patients with increased D0 had lower D0 than those with decreased D0(right-upper-lobe p ≤ 0.018). Conclusions In our SBRT cohort, the shifts towards the heart were not associated with worse OS. Moderate correlations were found between tumor and heart baseline shifts in each direction. Moreover, the distance between the PTV and the heart showed a significant correlation with shifts to the heart.