SBRT combined with concurrent chemoradiation in stage III NSCLC: Feasibility study of the phase I Hybrid trial.

Purpose: To assess the technical and clinical feasibility of the phase I Hybrid trial (NCT01933568), combining SBRT of the primary tumor (PT) and fractionated radiotherapy (FRT) to the lymph nodes (LN).

Materials And Methods: Ten patients with stage III NSCLC with a peripheral PT < 5 cm were prospectively selected. The EQD corrected normal tissue dose parameters of the FRT plan of 24×2.75 Gy to PT and 24×2.42 Gy to LN (IMRT) was compared with 3×18 Gy on the PT and 24×2.42 Gy on the LN (VMAT) using a Wilcoxon signed-rank test. To anticipate differential motion between PT and LN, worst-case scenarios for OAR were calculated. Electronic portal imaging device (EPID) dosimetry analysis was performed to rule out dosimetric errors during delivery.

Results: The Hybrid plans revealed a significant decrease of esophagus EUD n = 0.13, lung V5 and V20 and a significant increase in D of the PRV of the mediastinal envelope. Plans were robust against differential motion of 5 mm between PT and LN in 8 patients and failed in 2 patients due to spinal cord constraints. Average pass rates were ≥87% for EPID dosimetry.

Conclusions: SBRT and FRT could be combined within the given OAR constraints. Safety will be assessed in the Hybrid trial.