The T2 sequences were performed in a total scan time of 1 minute and 21 s (16s per breath hold), with a bandwidth of 781 Hertz per pixel (repetition time = 2000 ms, echo time = 98 ms, flip angle = 150°). The T1 and T1fs sequences were each performed in a single breath hold with a scan time of 19 seconds (s) and a spinal coil bandwidth of 490 Hertz per pixel (repetition time = 4.19 ms, echo time = 1.47 ms, flip angle = 9°). Three-dimensional (3D), noncontrast axial images were acquired on voluntary inhale breath hold and 3 sequences were performed at each timepoint: T1-weighted volumetric interpolated breath hold examination (VIBE), T1 fat-suppression (T1fs) spectrally adiabatic inversion recovery, and T2 half-Fourier acquisition single shot fast spin echo. Imaging was performed on an open bore 3.0-T Verio system (Siemens Medical Systems, Erlangen, Germany) incorporating an 8-channel Spine Matrix coil with an 8-channel torso coil placed on the chest, with a field-of-view of 400 mm, in-plane resolution of 1.3 × 1.3 mm, and slice and gap thicknesses of 3 mm and 0.5 mm. The clinically palpable breast tissue and surgical lumpectomy scar were outlined with radio-opaque wires.Īll patients underwent 2 sets of MRI in the same treatment position, the first before breast radiation therapy at a median time from planning CT of 1.9 days (range, 0-17), and the second in the final week of radiation therapy at a median time from the first MRI of 35 days (range, 18-67). Two-millimeter slices were acquired from midneck to below the diaphragm on a Brilliance wide-bore CT Scanner (Philips Medical Systems, Bothell, WA), with in-plane resolution of 1 mm x 1 mm. Patients initially underwent planning CT at a median time from surgery of 46 days (range, 14-187) in the supine position on an MT-350 breast board (CIVCO Medical Solutions, Kalona, IA), with the ipsilateral arm raised and abducted. The aims of this study were to investigate the interobserver variability in tumor bed delineation using 3 MRI sequences compared with CT at baseline and to quantify the change in tumor bed volume between pre- and end-of-treatment MRI for patients undergoing whole breast radiation therapy.
To our knowledge, only a single study has used MRI to investigate patterns of tumor bed volume change in the setting of PBI. 30, 31, 32, 33, 34 Adaptive planning may be useful for some patients who have significant reductions in the tumor bed volume over time.
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Several studies using serial CT scans have also found that the lumpectomy surgical bed significantly decreases in volume with time from surgery, which can lead to larger volumes of normal breast tissue being irradiated in boost and partial breast treatments. 25, 26, 27 Past investigations have used a variety of MRI sequences, but conclusions on the ideal sequence are inconsistent and uncertainty still exists. Previous investigations comparing the 2 modalities have yielded wide ranging results, however, with some finding no benefit of MRI over CT 21, 22, 23, 24 and others finding significant improvements in tumor bed visualization and CIs with the use of MRI. To further improve tumor bed visualization and interobserver variability in tumor bed delineation, magnetic resonance imaging (MRI) has been compared with CT. 12, 13, 14, 15, 17, 18 Surgical clips to delineate the tumor bed have been recommended, 19, 20 but this has not been uniformly adopted in North America, including at our center. 12, 13, 14, 15, 16 Features of the lumpectomy tumor bed on CT associated with lower interobserver agreement include small volume, low cavity visualization score (CVS), retroareolar location, dense breast parenchyma, and close proximity to the pectoralis muscle. 6, 7, 8Īlthough computed tomography (CT) is superior to clinical-based planning in defining the tumor bed volume, 9, 10, 11 studies have shown variable results in tumor bed delineation between observers, with conformity indices (CIs) between 0.31 and 0.76. 5 Accurate delineation of the lumpectomy tumor bed is therefore fundamental to the success of both breast boost and partial breast irradiation (PBI) in preventing LR. 4 LR risk is greatest within the region of the tumor bed. 1, 2, 3 An updated meta-analysis of randomized trials also reported a significant reduction in the risk of breast cancer death at 15 years. Multiple randomized controlled trials have established adjuvant radiation therapy after breast-conserving surgery as standard of care in the management of early-stage breast cancer to reduce the risk of local recurrence (LR).
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