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.
Zhang
Lifei
L
Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Garden
Adam S
AS
Lo
Justin
J
Ang
K Kian
KK
Ahamad
Anesa
A
Morrison
William H
WH
Rosenthal
David I
DI
Chambers
Mark S
MS
Zhu
X Ronald
XR
Mohan
Radhe
R
Dong
Lei
L
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*