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 (PTV60) and 50 Gy to elective volumes (PTV50). 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 V20Gy of the lungs and V40Gy 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.
Keywords: Intensity-modulated radiotherapy; Magnetic resonance imaging; Organs at risk; Squamous cell carcinomas; Volumetric modulated arc therapy.