230 - Quantifying Changes in Lung Function Using 4DCT-Based Ventilation Imaging for Patients Undergoing Functional Avoidance Radiation Therapy

Purpose/Objective(s): Functional avoidance radiation therapy has emerged as an innovative technique that utilizes functional imaging to optimize treatment by minimizing radiation dose to functional lung regions, thereby reducing pulmonary toxicity. This study aims to evaluate the correlation between imaging-based functional changes throughout treatment, radiation dose, and the development of radiation pneumonitis (RP) in patients undergoing functional avoidance radiation therapy (RT) using 4DCT-based ventilation imaging.

Materials/Methods: 50 patients from a prospective functional avoidance clinical trial treated with intensity-modulated radiotherapy at 2 institutions were included. Two 4DCT scans were acquired before RT and 3 months after RT. The pre-treatment and post-treatment lung ventilation imaging were derived from 4DCT scans and converted to percentile images. Dose maps were registered to the pre- and post-ventilation images via rigid registration. The voxels inside the lung region were stratified into nine regions of interest (ROIs) based on dose bins (5Gy-10Gy, 10Gy-15Gy, 15Gy-20Gy, 20Gy-25Gy, etc). Average ventilation change in each ROI was compared as a function of dose and radiation pneumonitis. In addition, linear regression was applied to correlate the ventilation change with the dose for each patient, and the slope was calculated. An unpaired T-test compared the ventilation changes between patients with grade = 2 (G2+) RP and grade 0 (G0) RP.

Results: Using the dose ROI data, lung regions receiving 15Gy-20 Gy and 20Gy -25Gy exhibited a significant decrease in function of -7.40% and -7.49% for G2+ RP patients, compared with G0 RP patients with function change of 1.00% and 1.29% (p=0.042 and p=0.026), respectively. The slope of G2+ RP patients exhibited a decline in function of -0.18±0.30% per Gy, while G0 RP patients produced a slope of 0.02± 0.40% per Gy (p=0.17).

Conclusion: The pattern of ventilation change as a function of radiation doses varies for patients undergoing functional avoidance therapy. A significant reduction in ventilation for lung regions receiving 15Gy-25Gy was observed for G2+ RP patients. The novelty of this work is that it shows that imaging-based functional changes can be an early predictive image biomarker for clinical toxicity.

Abstract 230 - Table 1