Effect of breathing motion on radiotherapy dose accumulation in the abdomen using deformable registration.
OBJECTIVE
To investigate the effect of breathing motion and dose accumulation on the planned radiotherapy dose to liver tumors and normal tissues using deformable image registration.


METHODS
Twenty-one free-breathing stereotactic liver cancer radiotherapy patients, planned on static exhale computed tomography (CT) for 27-60 Gy in six fractions, were included. A biomechanical model-based deformable image registration algorithm retrospectively deformed each exhale CT to inhale CT. This deformation map was combined with exhale and inhale dose grids from the treatment planning system to accumulate dose over the breathing cycle. Accumulation was also investigated using a simple rigid liver-to-liver registration. Changes to tumor and normal tissue dose were quantified.


RESULTS
Relative to static plans, mean dose change (range) after deformable dose accumulation (as % of prescription dose) was -1 (-14 to 8) to minimum tumor, -4 (-15 to 0) to maximum bowel, -4 (-25 to 1) to maximum duodenum, 2 (-1 to 9) to maximum esophagus, -2 (-13 to 4) to maximum stomach, 0 (-3 to 4) to mean liver, and -1 (-5 to 1) and -2 (-7 to 1) to mean left and right kidneys. Compared to deformable registration, rigid modeling had changes up to 8% to minimum tumor and 7% to maximum normal tissues.


CONCLUSIONS
Deformable registration and dose accumulation revealed potentially significant dose changes to either a tumor or normal tissue in the majority of cases as a result of breathing motion. These changes may not be accurately accounted for with rigid motion.
Velec
Michael
M
Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, Canada. michael.velec@rmp.uhn.on.ca
Moseley
Joanne L
JL
Eccles
Cynthia L
CL
Craig
Tim
T
Sharpe
Michael B
MB
Dawson
Laura A
LA
Brock
Kristy K
KK
D000465:Algorithms; D004386:Duodenum / Q000000981:diagnostic imaging; D004947:Esophagus / Q000000981:diagnostic imaging; D045853:Exhalation; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D001239:Inhalation; D007422:Intestines / Q000000981:diagnostic imaging; D007668:Kidney / Q000000981:diagnostic imaging; D008099:Liver / Q000000981:diagnostic imaging; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D009068:Movement; D011829:Radiation Dosage; D016634:Radiosurgery; D012119:Respiration; D013270:Stomach / Q000000981:diagnostic imaging