Pitch, roll, and yaw variations in patient positioning.
OBJECTIVE
To use pretreatment megavoltage-computed tomography (MVCT) scans to evaluate positioning variations in pitch, roll, and yaw for patients treated with helical tomotherapy.


METHODS
Twenty prostate and 15 head-and-neck cancer patients were selected. Pretreatment MVCT scans were performed before every treatment fraction and automatically registered to planning kilovoltage CT (KVCT) scans by bony landmarks. Image registration data were used to adjust patient setups before treatment. Corrections for pitch, roll, and yaw were recorded after bone registration, and data from fractions 1-5 and 16-20 were used to analyze mean rotational corrections.


RESULTS
For prostate patients, the means and standard deviations (in degrees) for pitch, roll, and yaw corrections were -0.60 +/- 1.42, 0.66 +/- 1.22, and -0.33 +/- 0.83. In head-and-neck patients, the means and standard deviations (in degrees) were -0.24 +/- 1.19, -0.12 +/- 1.53, and 0.25 +/- 1.42 for pitch, roll, and yaw, respectively. No significant difference in rotational variations was observed between Weeks 1 and 4 of treatment. Head-and-neck patients had significantly smaller pitch variation, but significantly larger yaw variation, than prostate patients. No difference was found in roll corrections between the two groups. Overall, 96.6% of the rotational corrections were less than 4 degrees.


CONCLUSIONS
The initial rotational setup errors for prostate and head-and-neck patients were all small in magnitude, statistically significant, but did not vary considerably during the course of radiotherapy. The data are relevant to couch hardware design for correcting rotational setup variations. There should be no theoretical difference between these data and data collected using cone beam KVCT on conventional linacs.
Kaiser
Adeel
A
Department of Radiation Oncology, University of California Irvine, Orange, CA, USA.
Schultheiss
Timothy E
TE
Wong
Jeffrey Y C
JY
Smith
David D
DD
Han
Chunhui
C
Vora
Nayana L
NL
Pezner
Richard D
RD
Chen
Yi-Jen
YJ
Radany
Eric H
EH
D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal; D012399:Rotation; D014057:Tomography, X-Ray Computed / Q000379:methods*