MR-guided Gated Stereotactic Radiation Therapy Delivery for Lung, Adrenal, and Pancreatic Tumors: A Geometric Analysis

Feasibility of stereotactic radiotherapy using a 1.5 T MR-linac: Multi-fraction treatment of pelvic lymph node oligometastases

“…With clinical feasibility having been established for multifraction stereotactic radiotherapy using the MR-linac, we are currently implementing MR-linac treatment for multiple lymph node oligometastases in pelvic or low para-aortic regions. Future treatment of abdominal lymph node metastases will likely require breathing motion management, such as the use of an abdominal compression device [15], an internal target volume (ITV) or future tracking and gating functionality of the treatment machine [16].…”

First prospective clinical evaluation of feasibility and patient acceptance of magnetic resonance-guided radiotherapy in Germany

“…A gating target (region of interest, ROI) was defined (either the tumor/resection cavity or a surrogate, e.g., vessel, bronchus in close proximity), and the gating boundary was selected as a numerical margin added to the target ranging between 3 and 4 mm at the discretion of the treating physician. Due to uncertainties in deformable registration and image noise possibly causing errors in contour tracking [17], a small percentage of target outside of the predefined boundary without triggering a beam-off event was allowed (threshold-ROI%) [17]. Threshold-ROI% was set to 3% for most of the cases and to values up to 7% in isolated special cases.…”

“…These new hybrid systems for MRgRT do not only offer three-dimensional MRI for soft tissue target and organ at risk visualization, but also allow for continuous cine-MRI before as well as during treatment [12,13]. Cine-MRI during treatment enables advanced motion management based on real-time soft tissue anatomic feedback such as treatment beam gating [11,16,17]. This eliminates the need for invasive implantation of fiducial markers as well as the application of internal target volumes (ITV) in order to account for intrafractional motion, and thereby offers the potential for margin reduction and hence a lower risk of ensuing toxicity [18].…”

Real‐time 4DMRI‐based internal target volume definition for moving lung tumors

“…The acquisition time of the 4DMRI was limited to 80 s due to technical reasons, which is shorter than 2D cine-MR imaging studies reported in literature. [33][34][35] However, the proposed method could be easily extended to longer acquisition times in the future to improve statistics to assure that the representative target motion of the day is captured. 22 The DIR steps introduce uncertainties that are difficult to quantify but that are expected to be counterbalanced by the higher representativity of the target motion description compared to a 4D-CT-based ITV definition.…”

“…5,6 Several studies have investigated intrafractional and interfractional changes with 2D cine-MRI. 6,[30][31][32][33][34][35] Cai et al 36 showed that the characterization of lung tumor motion with temporally resolved MRI is more representative than with 4D-CT, mainly due to improved statistics through longer acquisition times. 22 Hence, temporally resolved MRI can help to refine the ITV definition for treatment planning.…”