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

Abstract

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.

Intrafractional baseline drift during free breathing breast cancer radiation therapy

“…A limitation of our study is that the in-house laser system only tracks the position of the sternum in one dimension and therefore we are only able to describe the intrafraction movement in the AP direction. Most of the intrafraction movement due to muscle relaxation would occur in the AP direction, however, other authors have also described presence of intrafraction movement in the SI direction, which could be a consequence of the immobilization used [10,11].…”

“…Baseline drift occurs probably due to muscle relaxation in the shoulder region, and the drift is differentiated from baseline shifts that probably happen due to patient movement during treatment. There are some studies that have evaluated baseline drift for breast, liver and lung cancer [8][9][10][11][12]. To our knowledge there are no studies describing the baseline drift within each fraction and for all treatment sessions for a large population of breast cancer patients.…”

Real-time intra-fraction motion management in breast cancer radiotherapy: analysis of 2028 treatment sessions

“…[26] Similarly, another group used MRI with two time scales (2D and 3D MRI) showing a median deviation of about 2 vs. 2.2 mm. [27] MR-imaging during RT represents an elegant and promising approach to track target volumes in real time, especially in soft tissues including breast. Nevertheless, compared to other here described optical tracking systems, these image guided systems still remain very expensive and currently not widely available in clinical practice.…”

Motion management strategies and technical issues associated with stereotactic body radiotherapy of thoracic and upper abdominal tumors: A review from NRG oncology

“…Cine MRI images may be useful when treating without respiratory management particularly in patients with unreliable 4D CT imaging . Among other factors, the absence of ionizing radiation using MRI has facilitated the application of cine MRI for the development of motion models in several different treatment sites including the abdomen, thorax, liver, breast, and rectum among other sites. The emergence of online MRI‐guided radiation delivery has also permitted the increased utilization of cine MRI techniques for real‐time motion assessment and the construction of motion models …”