Simultaneous Integrated Dose Reduction Intensity-Modulated Radiotherapy Effectively Reduces Cardiac Irradiation Dose in Limited-Stage Small-Cell Lung Cancer

Abstract

To assess the clinical survival outcomes and toxicities of simultaneous dose reduction with intensity-modulated radiotherapy (SIR-IMRT) versus conventional IMRT (C-IMRT) in patients with limited-stage small cell lung cancer (LS-SCLC).After propensity score matching (PSM), a retrospective analysis of 320 patients with LS-SCLC who were treated using SIR-IMRT or C-IMRT from January 1, 2013 to December 31, 2018 was conducted. The prescribed irradiation dose in the SIR-IMRT cohort was 60 Gy to the planning gross tumor volume (PGTV) and 54 Gy to the planning target volume (PTV); in the C-IMRT cohort, the radiation dose was 60 Gy to both PGTV and PTV. Treatment-related toxicities, short-term effects, and survival outcomes were observed.Of the 320 patients (n = 160 patients in each group) included in the study, 196 (61.3%) were male, and the median patient age was 60 years. The median survival time (MST) was 31.3 (95% CI, 29.5-33.2) months, and the median progression-free survival (PFS) and locoregional recurrence-free survival (LRFS) were 18.1 (95% CI 13.6-23.5) months and 26.9 months, respectively. The MST in the two cohorts were 32.3 (95% CI, 29.8-34.8) months (SIR-IMRT) and 29.3 (95% CI 26.2-32.4) months (C-IMRT), respectively (P = 0.048). No differences in PFS and LRFS and no treatment failure were found between the two groups. Compared with the C-IMRT cohort, obviously lower radiation-related toxicities were observed in the SIR-IMRT cohort. In addition, the underlying dose was minimized in the SIR-IMRT treatment plans through critical thoracic organs at risk (OAR), and the percentage of Vheart20 - Vheart50 was obviously lower in the SIR-IMRT group (all P < 0.05). Further, the cardiac dose dosimetric parameter Vheart40 was found to have a negative association with survival (r = -0.21, P = 0.011). The ROC curve of Vheart40 was plotted by identifying 15.04% as a cut-off point, which that yielded 54.0% sensitivity and 69.2% specificity for predicting survival loss, and the area under the ROC curve was 0.612 (95% CI 0.538-0.686, P = 0.004).Compared with C-IMRT, SIR-IMRT minimizes the underlying dose to critical thoracic OARs. Lower radiation-related toxicity was observed in the SIR-IMRT group, without compromising local control and disease control. In addition, cardiac dose exposure was negatively associated with survival. Thus, 15.04% of Vheart40 is recommended as the cut-off point, and a value above 15.04% predicts survival loss.