Comparison of treatment plans for a high-field MRI-linac and a conventional linac for esophageal cancer

Abstract

Purpose: To compare radiotherapy treatments plans in esophageal cancer calculated for a high-field magnetic resonance imaging (MRI)-linac with plans for a conventional linac. Materials and methods: Ten patients with esophageal squamous cell carcinomas were re-planned retrospectively using the research version of Monaco (V 5.19.03, Elekta AB, Stockholm, Sweden). Intensity modulated radiotherapy (IMRT) plans with a nine-field step-and-shoot technique and two-arc volumetric modulated arc therapy (VMAT) plans were created for the Elekta MRI-linac and a conventional linac, respectively. The prescribed dose was 60 Gy to the primary tumor (PTV 60 ) and 50 Gy to elective volumes (PTV 50 ). Plans were optimized for optimal coverage of the 60 Gy volume and compared using dose–volume histogram parameters. Results: All calculated treatment plans met predefined criteria for target volume coverage and organs at risk dose both for MRI-linac and conventional linac. Plans for the MRI-linac had a lower number of segments and monitor units. No significant differences between both plans were seen in terms of V 20Gy of the lungs and V 40Gy of the heart with slightly higher mean doses to the heart (14.0 Gy vs. 12.5 Gy) and lungs (12.8 Gy vs. 12.2 Gy). Conclusion: Applying conventional target volume and margin concepts as well as dose-fractionation prescription reveals clinically acceptable dose distributions using hybrid MRI-linac in its current configuration compared to standard IMRT/VMAT. This represents an important prerequisite for future studies to investigate the clinical benefit of MRI-guided radiotherapy exploiting the conceptional advantages such as reduced margins, plan adaptation and biological individualization and hypofractionation.