Purpose: The purpose of this study was to quantify mid‐and post‐treatment changes in 4D‐CT ventilation and test the hypothesis: temporal changes of 4D‐CT ventilation in lung regions receiving high doses are greater than those in regions receiving low or no doses. Methods: In an IRB‐approved clinical trial, repeat 4D‐CT scans were acquired for eight thoracic cancer patients treated with conventionally‐fractionated or hypo‐fractionated radiotherapy at the following time points: pre‐treatment (8 patients), mid‐treatment (6) and post‐treatment (7). Ventilation images were created for each time point using deformable registration for spatial mapping of the peak‐exhale 4D‐CT image to the peak‐inhale image and computation of Jacobian‐based ventilation metric. To quantify the ventilation change between pre‐treatment (baseline) and mid‐or post‐treatment, rigid registration was performed and the ventilation values were normalized by the mean value in high‐functional (>50th percentile ventilation value) lung regions receiving low doses (biologically effective dose <30 Gy). Statistical significance was tested using a Wilcoxon test. Results: Absolute ventilation changes in the high dose ROI were found to be greater than those in the low dose ROI consistently for all patients at all time points, except for one case. Overall, the mean absolute ventilation change in the high dose ROI was 22.6±17.7%, which was significantly greater than that in the low dose ROI (5.0±3.7%) (p<0.01). Several patients showed clear correlations between 4D‐CT ventilation changes and anatomic changes observed in CT images. For example, patient 3 demonstrated increased ventilation, which was correlated with central airway re‐opening and tumor regression. Conclusion: An 8‐patient study demonstrated significantly greater changes of 4D‐CT ventilation in lung regions receiving high doses than those in regions receiving low or no doses, providing a validation for 4D‐CT ventilation imaging. Future studies will focus on detailed analysis of correlations between 4D‐CT ventilation changes and anatomic changes. National Lung Cancer Partnership Young Investigator Research Grant; NIH/NCI2 R01 CA 093626.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging