Accuracy and Utility of Deformable Image Registration in (68)Ga 4D PET/CT Assessment of Pulmonary Perfusion Changes During and After Lung Radiation Therapy.
OBJECTIVE
Measuring changes in lung perfusion resulting from radiation therapy dose requires registration of the functional imaging to the radiation therapy treatment planning scan. This study investigates registration accuracy and utility for positron emission tomography (PET)/computed tomography (CT) perfusion imaging in radiation therapy for non-small cell lung cancer.


METHODS
(68)Ga 4-dimensional PET/CT ventilation-perfusion imaging was performed before, during, and after radiation therapy for 5 patients. Rigid registration and deformable image registration (DIR) using B-splines and Demons algorithms was performed with the CT data to obtain a deformation map between the functional images and planning CT. Contour propagation accuracy and correspondence of anatomic features were used to assess registration accuracy. Wilcoxon signed-rank test was used to determine statistical significance. Changes in lung perfusion resulting from radiation therapy dose were calculated for each registration method for each patient and averaged over all patients.


RESULTS
With B-splines/Demons DIR, median distance to agreement between lung contours reduced modestly by 0.9/1.1 mm, 1.3/1.6 mm, and 1.3/1.6 mm for pretreatment, midtreatment, and posttreatment (P < .01 for all), and median Dice score between lung contours improved by 0.04/0.04, 0.05/0.05, and 0.05/0.05 for pretreatment, midtreatment, and posttreatment (P < .001 for all). Distance between anatomic features reduced with DIR by median 2.5 mm and 2.8 for pretreatment and midtreatment time points, respectively (P = .001) and 1.4 mm for posttreatment (P > .2). Poorer posttreatment results were likely caused by posttreatment pneumonitis and tumor regression. Up to 80% standardized uptake value loss in perfusion scans was observed. There was limited change in the loss in lung perfusion between registration methods; however, Demons resulted in larger interpatient variation compared with rigid and B-splines registration.


CONCLUSIONS
DIR accuracy in the data sets studied was variable depending on anatomic changes resulting from radiation therapy; caution must be exercised when using DIR in regions of low contrast or radiation pneumonitis. Lung perfusion reduces with increasing radiation therapy dose; however, DIR did not translate into significant changes in dose-response assessment.
Department of Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia. Electronic address: nick.hardcastle@gmail.com.
Nicholas
N
Hardcastle
Molecular Imaging, Centre for Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia.
Michael S
MS
Hofman
Molecular Imaging, Centre for Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia; Department of Medicine, University of Melbourne, Melbourne, Australia.
Rodney J
RJ
Hicks
Molecular Imaging, Centre for Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia.
Jason
J
Callahan
Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia; The Sir Peter MacCallum Department of Oncology, Melbourne University, Victoria, Australia.
Tomas
T
Kron
Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, East Melbourne, Australia; The Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia.
Michael P
MP
MacManus
Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, East Melbourne, Australia; The Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia.
David L
DL
Ball
Department of Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne, Australia.
Price
P
Jackson
Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, East Melbourne, Australia.
Shankar
S
Siva
D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000098:blood supply / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D005710:Gallium Radioisotopes; D006801:Humans; D008168:Lung / Q000098:blood supply / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000098:blood supply / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy; D010865:Pilot Projects; D049268:Positron-Emission Tomography / Q000379:methods*; D011446:Prospective Studies; D017564:Radiation Pneumonitis; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012680:Sensitivity and Specificity; D014692:Ventilation-Perfusion Ratio
D005710:Gallium Radioisotopes