Using in vivo respiratory-gated micro-computed tomography imaging to monitor pulmonary side effects in 10 MV FLASH and conventional radiotherapy

This study demonstrated a method that can characterize the development of FLASH and conventional radiotherapy-induced pulmonary complications with in vivo respiratory-gated micro-CT imaging methods in free-breathing mice. Thirty C57BL/6 mice were selected for this research project. Baseline respiratory-gated micro-CT images of individuals were collected a week before receiving treatments. During each imaging session, we collected two images for the end-expiration and peak-inspiration phases. Mice were equally distributed into five groups after baseline respiratory-gated micro-CT imaging sessions to receive different radiation treatments. Treatments administered included no irradiated, 10 MV photon ultra-high dose-rate radiotherapy (FLASH-RT) and conventional radiotherapy at two dose levels 15 Gy and 30 Gy targeting on lungs. Mice received repeated respiratory-gated micro-CT scans up to 24 weeks post treatment. For data analysis, regions of interest were drawn starting 2 mm above the carina and covering the entire lung. After selecting threshold numbers, we did semi-manual lung segmentation. The lung's morphological, structural, and functional information was measured to evaluate injuries in pulmonary tissues. Statistics analysis were performed using ANOVA repeated measurement. We monitored the development of lung inflammation, radiation pneumonitis, and fibrosis through respiratory-gated micro-CT images at different timelines, which were also confirmed with histogram analysis. We found significant differences between high-dose conventional and the control groups. Our study showed that the respiratory-gated imaging method can identify the development of pulmonary inflammation and radiation. The murine model suggested that conventional radiation treatment had more severe complications than the FLASH group. This experimental work is the first study using the in vivo respiratory-gated imaging method to monitor the progression of 10 MV photon FLASH-RT-induced pulmonary complications in free-breathing mice.Science, Faculty ofPhysics and Astronomy, Department ofGraduat