Dosimetric Impact of MRI distortions - A study on Head and Neck Cancers

The dosimetric impact of distortions on 21 head and neck cancer MR-only radiotherapy (RT) treatment plans was studied. Distorted CT (dCT) images were obtained by deforming patient CTs (CT) with displacement fields from residual system and patient-induced susceptibility effects. The feasibility of MR-only RT was demonstrated by a dose difference of less than 2% within the target volume for all dosimetric parameters evaluated between dCT and CT treatment plans. Active shimming over entire image volumes reduced distortions due to local B0-field inhomogeneities. However, shimming over user-defined sub-volumes introduced unwanted geometric shifts in nearby regions.

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