SU-F-J-120: Evaluation of the Combined Effect of Body Orientation and Breathing On Organ Movement in Thorax Using Multi-Step Deformable Image Registration.

PURPOSE: Use deformable registration to map more complex anatomies that include changes associated with both different body positions and breathing, and evaluate the resultant respiratory excursions for tumors and relevant organs at risk.

METHODS: Same-day exhale and inhale datasets from prone and supine 4D CT scans of lung cancer patients have been registered using the Elastix software package through a 3 step process: (1) rigid registration for bony alignment (2) deformable multiresolution B-Spline registration of entire anatomy (3) deformable multiresolution B-Spline registration of lung parenchyma (to improve lung vasculature alignment).Manual contours were propagated from the supine-inhale phase to supine-exhale, prone-exhale and prone-inhale, via the resulting registration transformations. Motion excursions between exhale and inhale for both body orientations were computed for tumors, heart, esophagus, vertebrae (T2, T5, T12).

RESULTS: The registration accuracy was evaluated by visual inspection of the deformed contours by physicians and minimal contour adjustments were made where deemed appropriate. The average supine [mm] / prone [mm] motion amplitudes for the initial 5-patient sample are as follows: Tumor - 5.8/6.5, T5 - 1.4/2.0, T2 - 0.5/1.6, T12 - 1.7/2.9, Heart- 4.9/9.0, Upper esophagus - 1.6/3.8, Middle esophagus - 3.8/5.0, Lower esophagus - 4.1/6.7. Differences between prone and supine excursions for heart, esophagus, T2 and T12 were significant at 95% level (one-sided Wilcoxon Mann-Whitney test).On average, the right and left lung volumes increased by 10% at inhale prone and by 5% at exhale prone from their respective values in supine position.

CONCLUSION: A multi-step deformable registration sequence was implemented and successfully used for supine-prone image registration of thorax. In prone position, lungs are larger, likely owing to increased pulmonary compliance and decreased compressive force of the heart on lungs when prone. Breathing motion excursion is enhanced in prone, possible consequence of rib cage stabilization and increased diaphragmatic motion. Elisabeth Weiss: Research support from Philips Healthcare and National Institutes of Health; Licensing agreement with Varian Medical Systems, UpToDate royalties.