Assessment of intrafractional movement and internal motion in radiotherapy of rectal cancer using megavoltage computed tomography.
OBJECTIVE
The aim of this study was to provide estimates of setup and internal margins of patients treated for rectal carcinoma using helical tomotherapy and to assess possible margin adaptations. Using helical tomotherapy, highly conformal dose distributions can be created, and the integrated megavoltage computed tomography (MVCT) modality allows very precise daily patient positioning. In clinical protocols, however, margins originating from traditional setup procedures are still being applied. This work investigates whether this modality can aid in redefining treatment margins.


METHODS
Ten patients who were treated with tomotherapy underwent MVCT scanning before and after 10 treatments. Using automatic registration the necessary setup margin was investigated by means of bony landmarks. Internal margins were assessed by delineating and describing the mesorectal movement.


RESULTS
Based on bony landmarks, movement of patients during treatments was limited to 2.45 mm, 1.99 mm, and 1.09 mm in the lateral, longitudinal, and vertical direction, respectively. Systematic errors were limited to <1 mm. Measured movement of the mesorectal space was -1.6 mm (+/- 4.2 mm) and 0.1 mm (+/- 4.0 mm) for left and right lateral direction. In the antero-posterior direction, mean shifts were -2 mm (+/- 6.8 mm) and -0.4 mm (+/- 3.8 mm). Mean shifts in the cranio-caudal direction were respectively -3.2 mm (+/- 5.6 mm) and -3.2 mm (+/- 6.8 mm).


CONCLUSIONS
The use of the integrated MVCT on the tomotherapy system can minimize the setup margin for rectal cancer, and can also be used to adequately describe the internal margin allowing for direct treatment margin adaptation.
Tournel
Koen
K
UZ Brussel, Oncologisch Centrum, Department of Radiotherapy, Brussels, Belgium. Koen.Tournel@uzbrussel.be
De Ridder
Mark
M
Engels
Benedikt
B
Bijdekerke
Paul
P
Fierens
Yves
Y
Duchateau
Michael
M
Linthout
Nadine
N
Reynders
Truus
T
Verellen
Dirk
D
Storme
Guy
G
D016477:Artifacts; D006801:Humans; D009068:Movement; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*