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Impact of Partial Volume Effect From Air in Pulmonary 18F-FDG PET as An Imaging Biomarker for Pulmonary Toxicity After Radiotherapy

L Sensoy1*, M E Daly1, T Yamamoto1, (1) UC Davis Medical Center, Sacramento, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Evidence indicates an association between increased (18)F-FDG uptake in the lungs before radiotherapy (RT) and pulmonary toxicity after RT. However, there are conflicting data on the effect of spatial overlap between lung regions with increased (18)F-FDG uptake and dose. Correction for partial volume averaging due to air within each voxel may allow a better localization of increased uptake regions. In this study we quantified the effect of tissue-fraction correction in (18)F-FDG-PET in lung cancer patients.

Methods:
Patients with stage I and III non-small cell lung cancer underwent standard-of-care staging (18)F-FDG-PET with low-dose CT prior to RT. CT images were resampled to match the resolution of PET images, and regions of interest (ROIs) were generated for both lungs so as to only include voxels with values between -1024 and -600 Hounsfield units (HUs). PET images were then masked by those ROIs and each voxel value was reassigned an (18)F-FDG uptake corrected for its tissue-fraction estimated using HUs in the corresponding CT. Finally, the original and corrected PET images were compared using the Spearman’s rank voxel-wise correlation coefficient.

Results:
The Spearman’s rank voxel-wise correlation between the original and tissue-fraction corrected PET images ranged from mild (0.436) to strong (0.929) (standard deviation: 0.218) for the whole lung, where the correlations for the right and left lungs were similar for each patient. Two patients who also had chronic obstructive pulmonary disease (COPD) had the lowest Spearman rank correlations (0.436 and 0.498), which can be explained by spatial heterogeneity of lung tissue fractions in those patients.

Conclusion:
The effect of tissue-fraction correction in pulmonary (18)F-FDG-PET varied widely between the five lung cancer patients, suggesting that the spatial location of high uptake regions may change after correction in some cases. This correction method may improve the predictive value of (18)F-FDG-PET for pulmonary toxicity following RT.

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