Quantification of intra-fraction motion in breast radiotherapy using supine magnetic resonance imaging

• Published in: Physics in medicine & biology 2016-02, Vol.61 (3), p.1352-1370
• Main Authors: van Heijst, Tristan C F, Philippens, Mariëlle E P, Charaghvandi, Ramona K, den Hartogh, Mariska D, Lagendijk, Jan J W, Desirée van den Bongard, H J G, van Asselen, Bram
• Format: Article
• Language: English
• Subjects: Adult; Aged; Algorithms; Breast Neoplasms - radiotherapy; breast radiotherapy; cine-MRI; Female; Humans; intra-fraction motion; magnetic resonance imaging; Magnetic Resonance Imaging - methods; Middle Aged; Motion; Radiotherapy, Computer-Assisted - methods; supine; Supine Position
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/61/3/1352

In early-stage breast-cancer patients, accelerated partial-breast irradiation techniques (APBI) and hypofractionation are increasingly implemented after breast-conserving surgery (BCS). For a safe and effective radiation therapy (RT), the influence of intra-fraction motion during dose delivery becomes more important as associated fraction durations increase and targets become smaller. Current image-guidance techniques are insufficient to characterize local target movement in high temporal and spatial resolution for extended durations. Magnetic resonance imaging (MRI) can provide high soft-tissue contrast, allow fast imaging, and acquire images during longer periods. The goal of this study was to quantify intra-fraction motion using MRI scans from 21 breast-cancer patients, before and after BCS, in supine RT position, on two time scales. High-temporal 2-dimensional (2D) MRI scans (cine-MRI), acquired every 0.3 s during 2 min, and three 3D MRI scans, acquired over 20 min, were performed. The tumor (bed) and whole breast were delineated on 3D scans and delineations were transferred to the cine-MRI series. Consecutive scans were rigidly registered and delineations were transformed accordingly. Motion in sub-second time-scale (derived from cine-MRI) was generally regular and limited to a median of 2 mm. Infrequently, large deviations were observed, induced by deep inspiration, but these were temporary. Movement on multi-minute scale (derived from 3D MRI) varied more, although medians were restricted to 2.2 mm or lower. Large whole-body displacements (up to 14 mm over 19 min) were sparsely observed. The impact of motion on standard RT techniques is likely small. However, in novel hypofractionated APBI techniques, whole-body shifts may affect adequate RT delivery, given the increasing fraction durations and smaller targets. Motion management may thus be required. For this, on-line MRI guidance could be provided by a hybrid MRI/RT modality, such as the University Medical Center Utrecht MRI linear accelerator.