TU‐G‐BRA‐04: Changes in Regional Lung Function Measured by 4D‐CT Ventilation Imaging for Thoracic Radiotherapy

Abstract

Purpose:To test the hypothesis: 4D‐CT ventilation imaging can show the known effects of radiotherapy on lung function: (1) radiation‐induced ventilation reductions, and (2) ventilation increases caused by tumor regression.Methods:Repeat 4D‐CT scans (pre‐, mid‐ and/or post‐treatment) were acquired prospectively for 11 thoracic cancer patients in an IRB‐approved clinical trial. A ventilation image for each time point was created using deformable image registration and the Hounsfield unit (HU)‐based or Jacobian‐based metric. The 11 patients were divided into two subgroups based on tumor volume reduction using a threshold of 5 cm3. To quantify radiation‐induced ventilation reduction, six patients who showed a small tumor volume reduction (<5 cm3) were analyzed for dose‐response relationships. To investigate ventilation increase caused by tumor regression, two of the other five patients were analyzed to compare ventilation changes in the lung lobes affected and unaffected by the tumor. The remaining three patients were excluded because there were no unaffected lobes.Results:Dose‐dependent reductions of HU‐based ventilation were observed in a majority of the patient‐specific dose‐response curves and in the population‐based dose‐response curve, whereas no clear relationship was seen for Jacobian‐based ventilation. The post‐treatment population‐based dose‐response curve of HU‐based ventilation demonstrated the average ventilation reductions of 20.9±7.0% at 35–40 Gy (equivalent dose in 2‐Gy fractions, EQD2), and 40.6±22.9% at 75–80 Gy EQD2. Remarkable ventilation increases in the affected lobes were observed for the two patients who showed an average tumor volume reduction of 37.1 cm3 and re‐opening airways. The mid‐treatment increase in HU‐based ventilation of patient 3 was 100.4% in the affected lobes, which was considerably greater than 7.8% in the unaffected lobes.Conclusion:This study has demonstrated that 4D‐CT ventilation imaging shows the known effects of radiotherapy on lung function: radiation‐induced ventilation reduction and ventilation increase caused by tumor regression, providing validation for 4D‐CT ventilation imaging.This study was supported in part by a National Lung Cancer Partnership Young Investigator Research grant.