SU-E-J-175: Comparison of Prone and Supine MRI Sequences for the Purpose of Radiotherapy Treatment Planning for Breast Cancer

Abstract

Purpose: The delineation of treatment volumes for breast cancer radiotherapy utilising standard CT images is associated with significant inter-observer variability. It has been proposed that MRI with improved quality soft tissue definition may reduce this inter-observer variability. The purpose of this study was to determine the optimum set-up and sequence for MRI-defined radiotherapy volume delineation. Methods: Six observers (2 radiologists, 4 radiation oncologists) were asked to score MRI quality for the purposes of radiotherapy delineation using the following scoring criteria where 0 — margin not recognisable (inability to discriminate) through to a score of 3, when margins were distinct (excellent discrimination). Supine breast MRI was achieved using a foam bridge to support a surface coil without touching the patient surface. T1 and T2 sequences were compared for both 1.5Tesla (1.5T) and 3T MRIs for a volunteer. Prone breast images were obtained using a 4 channel breast coil. Supine and prone breast MRIs were compared for T1 and T2 sequences for 3T for 2 volunteers. Results: Supine breast images were shown to be acceptable for the purpose of radiotherapy delineation with the 3T 2D T2 turbo spin echo sequences scoring 2s (fair discrimination) and 3s (excellent discrimination), most optimal. The prone 3D T1 gradient echo was the optimum of the supine and prone 3T images, however results were inconsistent with this sequence receiving a score of zero from one observer. Conclusion: Supine breast MRI scans can be achieved for the purpose of radiotherapy delineation. Scoring between observers was inconsistent when comparing scan sequences. This work has been supported by project grant 1033237 from Cancer Australia and The National Breast Cancer Foundation