Estimation of setup uncertainty using planar and MVCT imaging for gynecologic malignancies.
OBJECTIVE
This prospective study investigates gynecologic malignancy online treatment setup error corrections using planar kilovoltage/megavoltage (KV/MV) imaging and helical MV computed tomography (MVCT) imaging.


METHODS
Twenty patients were divided into two groups. The first group (10 patients) was imaged and treated using a conventional linear accelerator (LINAC) with image-guidance capabilities, whereas the second group (10 patients) was treated using tomotherapy with MVCT capabilities. Patients treated on the LINAC underwent planar KV and portal MV imaging and a two-dimensional image registration algorithm was used to match these images to digitally reconstructed radiographs (DRRs). Patients that were treated using tomotherapy underwent MVCT imaging, and a three-dimensional image registration algorithm was used to match planning CT to MVCT images. Subsequent repositioning shifts were applied before each treatment and recorded for further analysis. To assess intrafraction motion, 5 of the 10 patients treated on the LINAC underwent posttreatment planar imaging and DRR matching. Based on these data, patient position uncertainties along with estimated margins based on well-known recipes were determined.


RESULTS
The errors associated with patient positioning ranged from 0.13 cm to 0.38 cm, for patients imaged on LINAC and 0.13 cm to 0.48 cm for patients imaged on tomotherapy. Our institutional clinical target volume-PTV margin value of 0.7 cm lies inside the confidence interval of the margins established using both planar and MVCT imaging.


CONCLUSIONS
Use of high-quality daily planar imaging, volumetric MVCT imaging, and setup corrections yields excellent setup accuracy and can help reduce margins for the external beam treatment of gynecologic malignancies.
Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, St. Louis, MO 63110-1093, USA. lsantanam@radonc.wustl.edu
Lakshmi
L
Santanam
Jacqueline
J
Esthappan
Sasa
S
Mutic
Eric E
EE
Klein
S Murty
SM
Goddu
Summer
S
Chaudhari
Sasha
S
Wahab
Issam M
IM
El Naqa
Daniel A
DA
Low
Perry W
PW
Grigsby
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D016889:Endometrial Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery; D005260:Female; D006801:Humans; D008875:Middle Aged; D009068:Movement; D011187:Posture; D011446:Prospective Studies; D011832:Radiation Injuries / Q000517:prevention & control; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D036542:Tomography, Spiral Computed / Q000379:methods; D035501:Uncertainty; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery