(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: The purpose of the study was to investigate the suitability of treating esophageal cancer patients with the MRL and to characterize the dosimetric impact at heart tissue-air interfaces resulting primarily from the ERE.
Methods: We prospectively enrolled 20 cases with ESCC into a cohort study which underwent 4DCT and 3DCT scans before RT. The heart was contoured on 3DCT images, 4DCT end expiratory (EE) images, 4DCT MIP images and 4DCT AIP images by the same radiation oncologist. Radiotherapy plans were designed on 3DCT images and 0% phase of the 4DCT images, and the dose distributions of the plans were imported into MIM Maestro and deformed to each phase to generate distributions for MIP and AIP phases. In each case, we generated two types of plans:the original plan generated without a magnetic field;the optimized plan generated by a full optimization with a 1.5 T magnetic field. Variations in dose-volume parameters for the heart, pericardium were compared among different types. All the optimizations and calculations in this work were generated on Monaco 5.40.00.
Results: Most prominently, slight dose distortions at air-heart tissue-interfaces were observed in the presence of the magnetic field. Compared to non-magnetic field conditions, the dose of the magnetic field at air-tissue interfaces are slightly higher in some cases (1.8% of the tissue increased by 1.3 Gy on average). When considering cardiac activity, 4DCT is more affected by magnetic field than 3DCT. Heart dose was smaller at the 3DCT images (reduction = 3.12%, 4.23%, 4.35% on EE, MIP and AIP images, respectively, p < 0.05).
Conclusion: The dosimetric impact of magnetic field including the ERE at tissue-air boundaries can be observed on 3DCT and 4DCT during radiotherapy. The changes in heart dose may be valuable indicators of cardiac impairment and target dose changes when using the 1.5T linac.
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