SU‐C‐17A‐05: Quantification of Intra‐Fraction Motion of Breast Tumors Using Cine‐MRI

Abstract

Purpose: Magnetic resonance imaging (MRI) enables direct characterization of intra‐fraction motion ofbreast tumors, due to high softtissue contrast and geometric accuracy. The purpose is to analyzethis motion in early‐stage breast‐cancer patients using pre‐operative supine cine‐MRI. Methods: MRI was performed in 12 female early‐stage breast‐cancer patients on a 1.5‐T Ingenia (Philips)wide‐bore scanner in supine radiotherapy (RT) position, prior to breast‐conserving surgery. Twotwodimensional (2D) T2‐weighted balanced fast‐field echo (cine‐MRI) sequences were added tothe RT protocol, oriented through the tumor. They were alternately acquired in the transverse andsagittal planes, every 0.3 s during 1 min. A radiation oncologist delineated gross target volumes(GTVs) on 3D contrast‐enhanced MRI. Clinical target volumes (CTV = GTV + 15 mm isotropic)were generated and transferred onto the fifth time‐slice of the time‐series, to which subsequents lices were registered using a non‐rigid Bspline algorithm; delineations were transformed accordingly. To evaluate intra‐fraction CTV motion, deformation fields between the transformed delineations were derived to acquire the distance ensuring 95% surface coverage during scanning(P95%), for all in‐plane directions: anteriorposterior (AP), left‐right (LR), and caudal‐cranial(CC). Information on LR was derived from transverse scans, CC from sagittal scans, AP fromboth sets. Results: Time‐series with registration errors – induced by motion artifacts – were excluded by visual inspection. For our analysis, 11 transverse, and 8 sagittal time‐series were taken into account. Themedian P95% calculated in AP (19 series), CC (8), and LR (11) was 1.8 mm (range: 0.9–4.8), 1.7mm (0.8–3.6), and 1.0 mm (0.6–3.5), respectively. Conclusion: Intra‐fraction motion analysis of breast tumors was achieved using cine‐MRI. These first results show that in supine RT position, motion amplitudes are limited. This information can be used for adaptive RT planning, and to develop preoperative partial‐breast RT strategies, such asablative RT for early‐stage breast‐cancer patients.