Multiple regions-of-interest analysis of setup uncertainties for head-and-neck cancer radiotherapy.
OBJECTIVE
To analyze three-dimensional setup uncertainties for multiple regions of interest (ROIs) in head-and-neck region.


METHODS
In-room computed tomography (CT) scans were acquired using a CT-on-rails system for 14 patients. Three separate bony ROIs were defined: C2 and C6 vertebral bodies and the palatine process of the maxilla. Translational shifts of 3 ROIs were calculated relative to the marked isocenter on the immobilization mask.


RESULTS
The shifts for all 3 ROIs were highly correlated. However, noticeable differences on the order of 2-6 mm existed between any 2 ROIs, indicating the flexibility and/or rotational effect in the head-and-neck region. The palatine process of the maxilla had the smallest right-left shifts because of the tight lateral fit in the face mask, but the largest superior-inferior movement because of in-plane rotation and variations in jaw positions. The neck region (C6) had the largest right-left shifts. The positioning mouthpiece was found effective in reducing variations in the superior-inferior direction. There was no statistically significant improvement for using the S-board (8 out of 14 patients) vs. the short face mask.


CONCLUSIONS
We found variability in setup corrections for different regions of head-and-neck anatomy. These relative positional variations should be considered when making setup corrections or designing treatment margins.
Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Lifei
L
Zhang
Adam S
AS
Garden
Justin
J
Lo
K Kian
KK
Ang
Anesa
A
Ahamad
William H
WH
Morrison
David I
DI
Rosenthal
Mark S
MS
Chambers
X Ronald
XR
Zhu
Radhe
R
Mohan
Lei
L
Dong
D000465:Algorithms; D019583:Dose Fractionation, Radiation; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008397:Masks; D009064:Mouth Protectors; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D012149:Restraint, Physical / Q000295:instrumentation / Q000379:methods; D012399:Rotation; D014057:Tomography, X-Ray Computed / Q000379:methods*