Prophylactic cranial irradiation for limited-stage small-cell lung cancer patients: secondary findings from the prospective randomized phase 3 CONVERT trial

INTRODUCTION: The impact of the dose and fractionation of thoracic radiotherapy on the risk of developing brain metastasis (BM) has not been evaluated prospectively in LS-SCLC patients receiving prophylactic cerebral irradiation (PCI).

METHODS: Data in patients treated with PCI from the CONVERT trial was analysed.

RESULTS: 449/547 (82%) received PCI after completion of chemoradiotherapy. Baseline brain imaging consisted of CT-scan in 356/449 patients (79%) and MRI in 83/449 (18%) patients. PCI was delivered to 220/273 participants (81%) in the twice-daily (BD) group and 229/270 in the once-daily (OD) group (85%; p=0.49). Total median PCI dose was 25Gy in both BD and OD groups (p=0.74). In patients who received PCI, 75 (17%) developed BM (35 [8%] in OD and 40 [9%] in BD) and 173 (39%) other extracranial progression. In the univariate analysis, GTV was associated with an increased risk of BM (p=0.007) or other radiological progression events (p=0.006), whereas in a multivariate analysis both thoracic GTV (tGTV) and PS were associated with either progression type. The median OS of patients treated with PCI was 29 months. In the univariate analysis of OS, PCI timing from end of chemotherapy, weight loss >10%, and tGTV were prognostic factors associated with OS. In the multivariate analysis, only tGTV was associated with OS. Delay between end of chemotherapy and PCI was not associated with OS.

CONCLUSION: Patients receiving OD or BD thoracic RT have the same risk of developing BM. Larger tumours are associated with a higher risk of BM.