Delivery of magnetic resonance-guided single-fraction stereotactic lung radiotherapy

Abstract

Background and purpose: Single-fraction stereotactic ablative radiotherapy (SABR) is an effective treatment for early-stage lung cancer, but concerns remain about the accurate delivery of SABR in a single session. We evaluated the delivery of single-fraction lung SABR using magnetic resonance (MR)-guidance. Materials and methods: An MR-simulation was performed in 17 patients, seven of whom were found to be unsuitable, largely due to unreliable tracking of small tumors. Ten patients underwent single-fraction SABR to 34 Gy on a 0.35 T MR-linac system, with online plan adaptation. Gated breath-hold SABR was delivered using a planning target volume (PTV) margin of 5 mm, and a 3 mm gating window. Continuous MR-tracking of the gross tumor volume (GTV t) was performed in sagittal plane, with visual patient feedback provided using an in-room monitor. The real-time MR images were analyzed to determine precision and efficiency of gated delivery. Results: All but one patient completed treatment in a single session. The median total in-room procedure was 120 min, with a median SABR delivery session of 39 min. Review of 7.4 h of cine-MR imaging revealed a mean GTV t coverage by the PTV during beam-on of 99.6%. Breath-hold patterns were variable, resulting in a mean duty cycle efficiency of 51%, but GTV t coverage was not influenced due to real-time MR-guidance. On-table adaptation improved PTV coverage, but had limited impact on GTV doses. Conclusions: Single-fraction gated SABR of lung tumors can be performed with high precision using MR-guidance. However, improvements are needed to ensure MR-tracking of small tumors, and to reduce treatment times.

Single-Fraction Stereotactic Body Radiation Therapy: A Paradigm During the Coronavirus Disease 2019 (COVID-19) Pandemic and Beyond?

“…Future studies should evaluate whether such an approach is feasible for central lesions using novel image guidance modalities such as magnetic resonance imaging (MRI), which provides superior soft tissue visualization compared with computed tomography, continuous intrafraction visualization, and daily online adaptive replanning to achieve optimal target and normal organ doses. 30 , 31 …”

Influence of beam quality on reference dosimetry correction factors in magnetic resonance guided radiation therapy

“…Magnetic resonance-guided radiation therapy (MRgRT) is a new modality in image guided radiotherapy where the target position is determined by magnetic resonance imaging (MRI) in real-time before and during the irradiation. Because of the good MRI soft tissue contrast, this leads to an improved patient positioning and therefore also potentially to improved tumor conformity [1] , [2] , [3] , [4] .…”

A review of the role of MRI in diagnosis and treatment of early stage lung cancer

“…More recent reports have demonstrated the utility of adaptive MRgSBRT for high risk lung tumors, including central lesions, reirradiation, and in patients with interstitial lung disease, resulting in low rates of acute toxicity and promising initial local control [61]. Single fraction MRgSBRT to a total dose of 34 Gy has also been shown to be feasible, with a median delivery time of 39 minutes and a median in-room procedure time of 120 minutes [62].…”