Exploring the potential benefits of multi-field IMPT for stage I NSCLC SBRT: An in silico dosimetric comparison to IMRT and CyberKnife.

Purpose: Multi-field intensity-modulated proton therapy (IMPT) is a novel treatment protocol design method proposed to reduce range uncertainty. This study aimed to investigate whether multi-field IMPT has a dose distribution advantage over photon intensity-modulated radiation therapy (IMRT) and CyberKnife in stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC). Methods: Twenty-nine patients who underwent photon SBRT from February 2021 to September 2022 at Shandong Cancer Hospital were included. Their Computed Tomography (CT) images were used to design CyberKnife and multi-field IMPT plans. For the photon plan (IMRT and CyberKnife), the planning target volume (PTV), which was extended from the internal gross target volume (IGTV), was prescribed at 50 Gy. For the proton plans, the planning beam-specific target volume (PBSTV) based on the IGTV was created to meet the same area as the photon PTV. Multi-field IMPT was simulated by adding additional beam angles to conventional IMPT. Dose distribution assessment factors included Dmean and dose gradient index (GI) for PTV/PBSTV, and Dmean and the hottest 0.1 cm3 dose (D0.1cc) for organs at risk (OARs). Results: With each patient receiving 7-11 beams, multi-field IMPT had a better target GI than IMRT. For the lung, heart, spinal cord, chest wall, and ribs doses, the Dmean of the multi-field IMPT was smaller than that of the other two plans for all metrics. CyberKnife was significantly less protective of the OARs than the other two planning modalities, owing to the presence of a high target center dose. Conclusion: Multi-field IMPT achieves favorable target coverage and OAR protection compared to IMRT and CyberKnife for SBRT of NSCLC.