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Quantification of Intra-Fraction Motion of Breast Tumors Using Cine-MRI

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T van Heijst

T van Heijst*, M Philippens , D van den Bongard , B van Asselen , J Lagendijk , J Kleijnen , M den Hartogh , University Medical Center Utrecht, Utrecht, The Netherlands


SU-C-17A-5 Sunday 1:00PM - 1:55PM Room: 17A

Magnetic resonance imaging (MRI) enables direct characterization of intra-fraction motion of
breast tumors, due to high soft-tissue contrast and geometric accuracy. The purpose is to analyze
this motion in early-stage breast-cancer patients using pre-operative supine cine-MRI.

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. Two
two-dimensional (2D) T2-weighted balanced fast-field echo (cine-MRI) sequences were added to
the RT protocol, oriented through the tumor. They were alternately acquired in the transverse and
sagittal 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 subsequent
slices were registered using a non-rigid B-spline 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: anterior-posterior (AP), left-right (LR), and caudal-cranial
(CC). Information on LR was derived from transverse scans, CC from sagittal scans, AP from
both sets.

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. The
median P95% calculated in AP (19 series), CC (8), and LR (11) was 1.8 mm (range: 0.9-4.8), 1.7
mm (0.8-3.6), and 1.0 mm (0.6-3.5), respectively.

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 as
ablative RT for early-stage breast-cancer patients.

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