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

Abstract

Despite magnetic resonance imaging (MRI) being a mainstay in the oncologic care for many disease sites, it has not routinely been used in early lung cancer diagnosis, staging, and treatment. While MRI provides improved soft tissue contrast compared to computed tomography (CT), an advantage in multiple organs, the physical properties of the lungs and mediastinum create unique challenges for lung MRI. Although multi-detector CT remains the gold standard for lung imaging, advances in MRI technology have led to its increased clinical relevance in evaluating early stage lung cancer. Even though positron emission tomography is used more frequently in this context, functional MR imaging, including diffusion-weighted MRI and dynamic contrast-enhanced MRI, are emerging as useful modalities for both diagnosis and evaluation of treatment response for lung cancer. In parallel with these advances, the development of combined MRI and linear accelerator devices (MR-linacs), has spurred the integration of MRI into radiation treatment delivery in the form of MR-guided radiotherapy (MRgRT). Despite challenges for MRgRT in early stage lung cancer radiotherapy, early data utilizing MR-linacs shows potential for the treatment of early lung cancer. In both diagnosis and treatment, MRI is a promising modality for imaging early lung cancer.

Keywords: Diffusion magnetic resonance imaging; Image-guided; Lung neoplasms; Magnetic resonance imaging; Radiotherapy.

Fig. 1

Overview of challenges and advantages for the use of lung MRI in early lung cancer diagnosis and radiotherapy. CT = computed tomography; PET = positron-emission tomography; MRI = magnetic resonance imaging.

Fig. 2

Lung tumor delineation and treatment with MR-guided radiotherapy. A TRUFI sequence obtained on the MRIdian system (Mountain View, CA) for a central non-small cell lung cancer (NSCLC). MR-guided radiotherapy allows for daily adaptive therapy to decrease dose to nearby organs at risk (Aorta-Yellow; Esophagus-Blue; Spinal Cord-Green) while maintaining dose to the tumor (GTV (Gross Tumor Volume)-Orange). This patient was treated with stereotactic body radiotherapy (SBRT) 60 Gy in 8 fractions and has no evidence of progression of disease at 6 months. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Comparison between CT (a) and diffusion-weighted MR (b) images of the lungs (b-value = 200 smm⁻²). DWI detected hypointense intratumor vasculature (red arrow) and hyperintense small volume pleural effusion (green arrow), which were not discernible on CT. From the CT images it is unclear if the observed mediastinal lymph node was affected. Nevertheless, its increased signal intensity on DWI (yellow arrow) suggests its involvement. (Adapted from Kaza E. et al. Lung tumor radiotherapy treatment response assessment using Active Breathing Coordinated (ABC) Diffusion-Weighted Magnetic Resonance Imaging. Poster presentation at ISMRM 2016.) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

MRI CINE and gating for MR-guided stereotactic body radiotherapy. A MRI CINE via the MRIdian System (Mountain View, CA) of a patient undergoing stereotactic body radiotherapy (SBRT) to a tumor in the right lower lobe. The CINE runs at 4 frames/second and the tumor (green) is tracked by the MRIdian system. Treatment is not triggered until the tumor moves into the gating structure (red). We typically set the threshold of 95% of the tumor within the gating structure to activate treatment. There may be significant motion of lower lobe tumors when comparing expiration (A) to mid-breath (B) to inspiration (C). We perform the majority of treatments with deep inspiratory breath hold secondary to patient comfort and reproducibility. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)