WE‐C‐204B‐07: Real‐Time MRI for Soft‐Tissue‐Based IGRT of Moving and Deforming Lung Tumors

A. Sawant, k. Butts Pauly, M. Alley, S. Vasanawala, B. Loo, S. Joshi, J. Hinkle, P. Keall

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Purpose: Integrated MRI+Linacs can potentially provide real‐time soft‐tissue‐based image‐guidance for lung cancer IGRT. Towards this, we investigate guidance strategies using prospective rapid lung MRI coupled with deformable image registration. Method and Materials: All experiments were performed on a 1.5 T MRI scanner, using a 4‐channel cardiac coil, under free‐breathing conditions, without extrinisic contrast. A balanced steady‐state free precession (b‐SSFP) imaging sequence was optimized for prospective imaging and reconstruction. Two lung cancer patients (Pt#l: 4 cm tumor, right lower lobe, Pt#2: 6 cm tumor, left upper lobe) were imaged. A viscous fluid‐flow‐based deformable registration was applied to each MRI time series in order to determine motion trajectories of voxels within the field of view. These trajectories were used to characterize: (i) motion of the tumor centroid. (ii) relative trajectories of the tumor centroid and the diaphragmrelative trajectories of different points on the tumor — characterizing tumor rotation/deformation. Results: The modified b‐SSFP sequence yielded acquisition times of ∼0.16s and ∼1.5s for 2D and 3D acquisition, respectively. Tumor trajectory analysis: (i) significant cycle‐to‐cycle variation in tumor motion was observed in both patients (ii) For Pt#l, the tumor centroid showed good correlation with diaphragmatic motion. For Pt#2, this correlation was relatively poor (iii) Pt#l did not exhibit significant tumor rotation/deformation. In Pt.#2, the trajectories of two points on the tumor showed maximum deviations of ∼8 mm (superior‐inferior) and 3.4 mm (anterior‐posterior), indicating non‐negligible rotation/deformation likely due to the influence of the adjacent cardiac wall. Conclusion: To our knowledge, this is the first demonstration of MRI for real‐time imaging of lung cancer. The incorporation of these strategies into MRI+Linacs offers image‐guidance capabilities that are not possible using current techniques: (i) soft‐tissue‐based rather than surrogate‐based monitoring (ii) no fiducial implantation or imaging dose (iii) arbitrary slice selection and (iv) ability to monitor complex motion.

Original languageEnglish (US)
Number of pages1
JournalMedical physics
Issue number6
StatePublished - Jun 2010

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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