Normal lung tissue response following hypofractionated radiation based on radiological parameters
2019
Objective
To study dose-response relationships of fractionated irradiation induced pulmonary fibrosis in mice according to radiological imaging changes of lung.
Methods
A total of 8-10 week old-female C57BL6 mice were randomized into different groups for whole thoracic irradiation. The prescribed doses were 0, 2.0, 4.0, 6.0, 7.0, 8.5 Gy per fraction in a total of 5 fractions. CT imaging was performed at 24 weeks post irradiation. The averaged lung density and volume changes were obtained by the three-dimensional segmentation algorithm, and further analyzed in Boltzmann regression modeling.
Results
At the endpoint of 24 weeks, the dose-dependent pulmonary radiological alternations were revealed by coronal view of CT images. Translational analysis of fibrosis-related gene-signatures as well as histological collagen stainings further corroborated the radiological findings. According to Boltzmann modeling, the E50 of radiation-induced lung density changes was found to be (30.80±0.80)Gy (adjusted R2=0.97); whereas the E50 for radiation-induced lung volume reduction was determined as (31.31±7.07)Gy (adjusted R2=0.92). Both outcomes indicated a remarkable enhancement of tolerance to normal lung tissues after exposure with 5-fraction versus single fraction scheme.
Conclusions
The radiation-induced lung density and volume changes depend not only on total dose, but also the number and dose of fractions.
Key words:
Radiation fractionation; Radiation induced lung fibrosis; Boltzmann model; Radiobiological modeling
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