Comparison of Simultaneous Integrated Boost IMRT for Dose Escalation (54 Gy) and Conventional IMRT (45 Gy) Twice Daily Combined with Concurrent Chemotherapy for Limited-Stage Small-Cell Lung Cancer: Analysis of Two Prospective Trials

Abstract

<h3>Purpose/Objective(s)</h3> Twice-daily thoracic radiotherapy (TRT) with concurrent chemotherapy is standard for limited-stage small-cell lung cancer (LS-SCLC). However, the importance of twice-daily simultaneous integrated boost intensity-modulated radiotherapy (SIB-IMRT) has not been clearly defined in LS-SCLC. Therefore, we conducted a prospective single arm, multicenter phase II study of SIB-IMRT for dose escalation (54 Gy) to the gross tumor volume for LS-SCLC. Here, we compared SIB-IMRT for dose escalation (54 Gy) to the gross tumor volume versus conventional intensity-modulated radiotherapy (IMRT) of standard-dose (45 Gy) twice-daily combined with concurrent chemotherapy in patients with LS-SCLC. <h3>Materials/Methods</h3> Sixty patients with LS-SCLC were entered from 2015 to 2021 in the phase II study of SIB-IMRT, and all 60 patients were treated with SIB-IMRT to the postchemotherapy tumor volume, as the SIB-IMRT group. In the SIB-IMRT group, the prescribed dose was 54Gy at 1.8 Gy twice daily to PGTV, and 45 Gy at 1.5 Gy twice daily to PCTV. We previously conducted a prospective phase III study on thoracic radiotherapy (TRT) target volumes for LS-SCLC (Cancer, 2020, 126(4), 840-849). In that study, from 2012-2017, 85 patients received thoracic IMRT to the postchemotherapy tumor volume, as the IMRT group. In the IMRT group, the prescribed dose was 45 Gy at 1.5 Gy per twice-daily fraction to both the planning gross tumor volume (PGTV) and the planning clinical tumor volume (PCTV). All of the 145 patients in both groups received concurrent chemoradiotherapy (CCRT) after completion of 2 cycles of induction cisplatin-etoposide chemotherapy, and received chemotherapy for 4 to 6 cycles in total. We compared progression free survival (PFS) and overall survival (OS) between the treatment groups by using the Kaplan-Meier method. <h3>Results</h3> Overall, with a median follow-up of 34.6 months, the median PFS and OS were 11.9 and 23.7 months, respectively. The patients in the SIB-IMRT group showed marginal longer PFS than those in the IMRT group (13.3 months versus 11.5 months; <i>p</i> = 0.08). The median OS of the SIB-IMRT and IMRT groups were 35.0 and 20.3 months, with the 2-year OS rate of 66.1% and 38.8%, respectively (<i>p</i> =0.007). For radiotherapy toxicity, grade 2 acute esophagitis was more common in the SIB-IMRT group, but grade≥3 esophagitis and grade≥2 pneumonitis was no difference in both two groups. <h3>Conclusion</h3> For LS-SCLC patients, SIB-IMRT for dose escalation (54 Gy at 1.8Gy twice daily) to PGTV benefited survival greatly. Our results suggest that SIR-IMRT is safe and effective for patients with LS-SCLC and should be further evaluated in a large prospective clinical trial.