Measuring interfractional and intrafractional motion with cone beam computed tomography and an optical localization system for lower extremity soft tissue sarcoma patients treated with preoperative intensity-modulated radiation therapy.
OBJECTIVE
To evaluate inter- and intrafractional motion and rotational error for lower extremity soft tissue sarcoma patients by using cone beam computed tomography (CBCT) and an optical localization system.


METHODS
Thirty-one immobilized patients received CBCT image-guided intensity-modulated radiation therapy. Setup deviations of >3 mm from the planned isocenter were corrected. A second CBCT acquired before treatment delivery was registered to the planning CT to estimate interfractional setup error retrospectively. Interfractional error and rotational error were calculated in the left-right (LR), superoinferior (SI), and anteroposterior (AP) dimensions. Intrafractional motion was assessed by calculating the maximum relative displacement of optical localization system reflective markers placed on the patient's surface, combined with pre- and postfraction CBCT performed for 17 of the 31 patients once per week. The overall systematic error (SE) and random error (RE) were calculated for the interfractional and intrafractional motion for planning target volume margin calculation.


RESULTS
The standard deviation (SD) of the interfractional RE was 1.9 mm LR, 2.1 mm SI, and 1.8 mm AP, and the SE SD was 0.6 mm, 1.2 mm, and 0.7 mm in each dimension, respectively. The overall rotation (inter- and intrafractional) had an RE SD of 0.8° LR, 1.7° SI, and 0.7° AP and an SE SD of 1.1° LR, 1.3° SI, and 0.3° AP. The SD of the overall intrafractional RE was 1.6 mm LR, 1.6 mm SI, and 1.4 mm AP, and the SE SD was 0.7 mm AP, 0.6 mm SI, and 0.6 mm AP.


CONCLUSIONS
A uniform 5-mm planning target volume margin was quantified for lower extremity soft tissue sarcoma patients and has been implemented clinically for image-guided intensity-modulated radiation therapy.
Dickie
Colleen I
CI
Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario, Canada. Colleen.dickie@rmp.uhn.on.ca
Parent
Amy L
AL
Chung
Peter W M
PW
Catton
Charles N
CN
Craig
Tim
T
Griffin
Anthony M
AM
Panzarella
Tony
T
Ferguson
Peter C
PC
Wunder
Jay S
JS
Bell
Robert S
RS
Sharpe
Michael B
MB
O'Sullivan
Brian
B
D054893:Cone-Beam Computed Tomography; D006801:Humans; D035002:Lower Extremity / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D009068:Movement; D011300:Preoperative Care; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D012399:Rotation; D012509:Sarcoma / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000601:surgery