Residual Post-Treatment FDG Avidity in Regional Lymph Nodes Impacts Local-Regional Control in Patients Receiving Definitive Chemoradiation for Non-small Cell Lung Cancer: A Secondary Analysis of ACRIN 6668/RTOG 0235

Abstract

difficult to validate due to the lack of ground truth. This study aims to investigate a novel method, 3D Hyperpolarized Helium-3 (HP He3) tagging MRI, for evaluating lung ventilations and strains from direct measurements of lung deformation during breathing. Materials/Methods: A three-dimensional (3D) HP He-3 tagging MRI technique was developed for direct measurement of regional lung respiratory motion. Two healthy subjects were imaged under IRB-approved protocol at the end-of-inhalation (EOI) and end-of-exhalation (EOE) phases in a single scan using the HP He-3 MRI tagging technique. The 3D displacement vector field (DVF) of the lung between the EOI and EOE phases was determined by tracking the movements of the center of mass (CM) of the tagging grids in the HP He-3 MR tagging images. The strain tensor, which characterizes the 3D deformation of the grid, was computed from the relative displacements between the CM of each grid and its six nearest neighbors. Ventilations were then calculated using the principal strains (i.e., the eigenvalues of the strain tensor). Results: DVFs and volumetric maps of lung principal strains and ventilation were successfully generated for both subjects. Although Subject #1 had much larger respiratory motion amplitude than Subject #2 (5.8 0.5 cm vs. 3.6 0.5 cm), the first and second principal strains of the two subjects were found to be comparable (e1Z -0.45 0.03, e2Z -0.38 0.03, and e3Z -0.1 0.3 for Subject #1, and e1Z -0.41 0.02, e2Z -0.38 0.01, and e3Z -0.32 0.04 for Subject #2). The average ventilations in the left and the right lungs of two subjects were -73% 6% (left)/-62% 16% (right) and -72% 2% (left)/-71% 1% (right), respectively. Lung fissures were identifiable in the principal strain maps by larger values of e1 (-0.49 0.02), which results from the significant relative motions between lung lobes. Conclusions: A systematic approach was developed to generate 3D functional maps of ventilation and principal strains using HP He-3 tagging MR images obtained at different respiratory phases. This method holds great promise for revealing ground truth information about lung ventilation and strain, which may be applied to validate DIR based calculation, as well as for studying lung biomechanics. Author Disclosure: T. Cui: None. Q. Huang: None. W.G. Miller: None. X. Zhong: None. F. Yin: None. J. Cai: None.