Analysis of Long-Term 4-Dimensional Computed Tomography Regional Ventilation After Radiation Therapy

Purpose: To determine whether regional ventilation, as measured using 4-dimensional computed tomography (4D-CT), declines after radiation therapy (RT). Methods and Materials: We analyzed pretreatment 4D-CT scans associated with 2 RT courses. We quantified regional pulmonary function over equivalent dose in 2 Gy (EQD2(alpha/beta=3)) intervals of 0 to 5 Gy, 5 to 20 Gy, 20 to 40 Gy, and >40 Gy using percentile-normalized intensity-based (Vent(Int)) and Jacobian-based (Vent(Jac)) ventilation metrics. We modeled the impact of dose on mean ventilation ((Vent) over bar) and regional tidal volume (rTV: tidal volume [TV] within a dose interval normalized to total lung TV). We also identified clinical and dosimetric factors that affected regional ventilation changes (Delta(Vent) over bar and Delta rTV) after RT for the >20 Gy dose interval. Results: After RT, (Vent) over bar (Int) exhibited statistically significant dose-dependent declines within the 20 to 40 Gy (-5.0%; P=.03) and >40 Gy (-6.8%; P<.01) intervals. <(Vent)over bar>(Jac) exhibited a declining trend after RT only for the >40 Gy interval (-4.6%; P=.07). Factors associated with Delta(Vent) over bar (Int) for the >20 Gy dose interval included airway stenosis progression (P=.03) and gross tumor volume (P=.09). Both rTV(Int) and rTV(Jac) were associated with small (<2%) but significant declines after RT for 20 to 40 Gy and >40 Gy intervals. Factors associated with declining rTV(Int) (P<.05) for the >20 Gy dose interval included airway stenosis progression, greater V20 (volume of lung receiving >20 Gy), and smaller fraction of emphysema in V20. The association between the absence of chronic obstructive pulmonary disease and declining rTV trended toward significance (P=.09). Conclusions: Regional ventilation, as measured using 4D-CT, demonstrates a dose-dependent decline after RT. Our results support the use of 4D-CT ventilation imaging for monitoring regional pulmonary function change after RT. (C) 2015 Elsevier Inc. All rights reserved.