Potential of image-guidance, gating and real-time tracking to improve accuracy in pulmonary stereotactic body radiotherapy.
OBJECTIVE
To evaluate the potential of image-guidance, gating and real-time tumor tracking to improve accuracy in pulmonary stereotactic body radiotherapy (SBRT).


METHODS
Safety margins for compensation of inter- and intra-fractional uncertainties of the target position were calculated based on SBRT treatments of 43 patients with pre- and post-treatment cone-beam CT imaging. Safety margins for compensation of breathing motion were evaluated for 17 pulmonary tumors using respiratory correlated CT, model-based segmentation of 4D-CT images and voxel-based dose accumulation; the target in the mid-ventilation position was the reference.


RESULTS
Because of large inter-fractional base-line shifts of the tumor, stereotactic patient positioning and image-guidance based on the bony anatomy required safety margins of 12 mm and 9 mm, respectively. Four-dimensional image-guidance targeting the tumor itself and intra-fractional tumor tracking reduced margins to <5 mm and <3 mm, respectively. Additional safety margins are required to compensate for breathing motion. A quadratic relationship between tumor motion and margins for motion compensation was observed: safety margins of 2.4mm and 6mm were calculated for compensation of 10 mm and 20 mm motion amplitudes in cranio-caudal direction, respectively.


CONCLUSIONS
Four-dimensional image-guidance with pre-treatment verification of the target position and online correction of errors reduced safety margins most effectively in pulmonary SBRT.
Department of Radiation Oncology, Julius-Maximilians University, Wuerzburg, Germany. guckenberger_m@klinik.uni-wuerzburg.de
Matthias
M
Guckenberger
Thomas
T
Krieger
Anne
A
Richter
Kurt
K
Baier
Juergen
J
Wilbert
Reinhart A
RA
Sweeney
Michael
M
Flentje
D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000601:surgery*; D011857:Radiographic Image Interpretation, Computer-Assisted; D015641:Radiography, Interventional / Q000379:methods*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*