Analysis of Long-Term 4-Dimensional Computed Tomography Regional Ventilation After Radiation Therapy.
OBJECTIVE
To determine whether regional ventilation, as measured using 4-dimensional computed tomography (4D-CT), declines after radiation therapy (RT).


METHODS
We analyzed pretreatment 4D-CT scans associated with 2 RT courses. We quantified regional pulmonary function over equivalent dose in 2 Gy (EQD2α/β=3) intervals of 0 to 5 Gy, 5 to 20 Gy, 20 to 40 Gy, and >40 Gy using percentile-normalized intensity-based (VentInt) and Jacobian-based (VentJac) ventilation metrics. We modeled the impact of dose on mean ventilation (Vent¯) 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 (ΔVent¯ and ΔrTV) after RT for the >20 Gy dose interval.


RESULTS
After RT, Vent¯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¯Jac exhibited a declining trend after RT only for the >40 Gy interval (-4.6%; P=.07). Factors associated with ΔVent¯Int for the >20 Gy dose interval included airway stenosis progression (P=.03) and gross tumor volume (P=.09). Both rTVInt and rTVJac were associated with small (<2%) but significant declines after RT for 20 to 40 Gy and >40 Gy intervals. Factors associated with declining rTVInt (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.
Department of Radiation Oncology, Stanford University, Stanford, California. Electronic address: mking1@stanford.edu.
Martin T
MT
King
Department of Radiation Oncology, Stanford University, Stanford, California.
Peter G
PG
Maxim
Department of Radiation Oncology, Stanford University, Stanford, California.
Maximilian
M
Diehn
Department of Radiation Oncology, Stanford University, Stanford, California.
Billy W
BW
Loo
Department of Radiation Oncology, Stanford University, Stanford, California.
Lei
L
Xing
D000368:Aged; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000532:radiotherapy*; D008297:Male; D029424:Pulmonary Disease, Chronic Obstructive; D017564:Radiation Pneumonitis / Q000000981:diagnostic imaging; D011879:Radiotherapy Dosage; D012044:Regression Analysis; D012119:Respiration / Q000528:radiation effects*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D013990:Tidal Volume / Q000502:physiology / Q000528:radiation effects