Quantification of regional ventilation from treatment planning CT.
OBJECTIVE
We describe a method of quantifying regional ventilation from the radiotherapy treatment planning computed tomography (CT) images, with the goal of developing functional images for treatment planning and optimization.


METHODS
A series of exhalation breath-hold (eBH-CT) and inhalation breath-hold (iBH-CT) CT images obtained using a feedback-guided breath-hold technique for radiotherapy treatment planning was selected. The eBH-CT was mapped on a voxel-by-voxel basis to the iBH-CT using a deformable image registration algorithm. By using the average CT number over a 3 mm(3) region surrounding each pair of mapped voxels, the change in fraction of air per voxel (i.e., regional ventilation) was calculated. This methodology was applied to a series of 22 patients. The calculated total ventilation was compared to the change in contoured lung volumes between the exhalation and inhalation CTs (measured tidal volume).


RESULTS
A significant correlation was found between the calculated and measured tidal volumes for the left (R = 0.982) and right (R = 0.985), and for both lungs combined (R = 0.985). In the resulting images, the regional ventilation was highly variable and corresponded with the spatial distribution of differences in the CT values (Hounsfield units) between the eBH-CT and the iBH-CT images.


CONCLUSIONS
A method of quantifying regional ventilation from radiotherapy treatment planning CT data sets was demonstrated. The ventilation images can be used in plan optimization to minimize injury to functioning lung.
Guerrero
Thomas
T
Division of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. tguerrero@mdanderson.org
Sanders
Kevin
K
Noyola-Martinez
Josue
J
Castillo
Edward
E
Zhang
Yin
Y
Tapia
Richard
R
Guerra
Rudy
R
Borghero
Yerko
Y
Komaki
Ritsuko
R
D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008176:Lung Volume Measurements; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration; D014057:Tomography, X-Ray Computed