Establishing a Relationship Between Radiosensitivity of Lung Tissue and Ventilation

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Purpose/Objective(s)

Radiation therapy (RT) induced symptomatic pneumonitis is a significant problem for patients with tumors of the thorax; predicting RT-induced pulmonary toxicity remains elusive. The purpose of this study was to determine if the radiosensitivity of lung tissue is greater in regions with increased ventilation.

Materials/Methods

Eight subjects from a prospective IRB approved clinical trial were analyzed. 6-10 MV X-ray treatments were prescribed for doses between 61.2 to 70 Gy in 2 Gy fractions. Pulmonary function was derived for each voxel of the lung from 4DCT scans using deformable image registration techniques. The Jacobian determinant of the deformation map yielded the spatial distribution of ventilation for each subject. Patient specific changes in ventilation maps from 4DCT scans acquired prior to and 3 months

Results

Subjects showed a clear relationship between regions irradiated and a decline in pulmonary function. In univariate analysis a strong correlation was found (r2 = 0.92) between calculated radiation dose to a voxel and the PFC observed 3 months post-RT. PFC correlated strongly with the initial pulmonary function of the lung tissue (r2 = 0.97); dose differences in those tissues were negligible (<1 Gy mean dose). The DRC for regions of lung with minimal lung function had a linear regression line

Conclusions

Regions of increasing pre-RT lung function show greater fractional reduction in function post-RT. Our data reveals the increased sensitivity of high functioning lung, providing direct support for the hypothesis that improved oxygenation via ventilation increases the radiosensitivity of lung tissue.

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Author Disclosure: J. Bayouth: None. K. Du: None. G. Christensen: None. B. Smith: None. J. Buatti: None. J. Reinhardt: None.

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