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Comparison of 4D-CT Ventilation Imaging with SPECT Ventilation Imaging for Thoracic Cancer Patients

T Yamamoto

T Yamamoto1,2*, S Kabus3, C Lorenz3, E Mittra1, M Goris1, J Hong1, M Chung1, C Barquero1, N Eclov1, M Diehn1, B Loo1, P Keall4, (1) Stanford University, Stanford, CA, (2) University of California Davis, Sacramento, CA, (3) Philips Research, Hamburg, Germany, (4) University of Sydney, Sydney, Australia

WE-C-WAB-4 Wednesday 10:30AM - 12:30PM Room: Wabash Ballroom

Purpose: A novel lung ventilation imaging technique based on 4D-CT can be used for functional avoidance to spare high-functional lung regions, and early prediction or assessment of pulmonary toxicity in radiotherapy. However, there has been minimal validation showing inconsistent results in human subjects. The purpose of this study was to compare 4D-CT ventilation images with SPECT ventilation images as clinical reference.

Methods: In an IRB-approved clinical trial, 4D-CT ventilation and SPECT ventilation images were acquired in the supine position for 12 thoracic cancer patients. 4D-CT ventilation was calculated by deformable image registration of 4D-CT images, followed by analysis of the resultant displacement vector field to quantify regional volume change (Jacobian), a surrogate for ventilation. SPECT ventilation scans were performed by inhalation of 99mTc-DTPA aerosols. We evaluated the physiologic accuracy of 4D-CT ventilation by: (1) comparing 4D-CT ventilation values in SPECT ventilation defect regions with those in non-defect regions; (2) quantifying Dice similarity coefficients (DSCs) for the spatial overlap of low-functional lung regions determined by 4D-CT ventilation and SPECT ventilation; (3) comparing a ventral-to-dorsal gradient of 4D-CT ventilation with that of SPECT ventilation.

Results: Five patients showed severe depositions of SPECT DTPA aerosols in central airways, and hence were excluded from the analysis. The 4D-CT ventilation value in SPECT ventilation defect regions was found to be significantly lower than that in non-defect regions (0.14±0.06 vs. 0.19±0.07, p=0.01). The DSC for the spatial overlap of low-functional lung regions was weak (0.29±0.11). 4D-CT ventilation demonstrated a ventral-to-dorsal gravitational gradient, which was consistent with SPECT ventilation.

Conclusion: A 12-patient study demonstrated reasonable correlations between 4D-CT ventilation and SPECT ventilation as clinical reference, indicating the potential for 4D-CT ventilation imaging to achieve high physiologic accuracy. However, poor DSCs suggest the need for further studies to improve 4D-CT ventilation imaging and/or a validation study design.

Funding Support, Disclosures, and Conflict of Interest: National Lung Cancer Partnership Young Investigator Research Grant; NIH/NCI 2 R01 CA 093626

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