Refinement of treatment setup and target localization accuracy using three-dimensional cone-beam computed tomography for stereotactic body radiotherapy.
OBJECTIVE
To quantitatively compare two-dimensional (2D) orthogonal kV with three-dimensional (3D) cone-beam CT (CBCT) for target localization; and to assess intrafraction motion with kV images in patients undergoing stereotactic body radiotherapy (SBRT).


METHODS
A total of 50 patients with 58 lesions received 178 fractions of SBRT. After clinical setup using in-room lasers and skin/cradle marks placed at simulation, patients were imaged and repositioned according to orthogonal kV/MV registration of bony landmarks to digitally reconstructed radiographs from the planning CT. A subsequent CBCT was registered to the planning CT using soft tissue information, and the resultant "residual error" was measured and corrected before treatment. Posttreatment 2D kV and/or 3D CBCT images were compared with pretreatment images to determine any intrafractional position changes. Absolute averages, statistical means, standard deviations, and root mean square (RMS) values of observed setup error were calculated.


RESULTS
After initial setup to external marks with laser guidance, 2D kV images revealed vector mean setup deviations of 0.67 cm (RMS). Cone-beam CT detected residual setup deviations of 0.41 cm (RMS). Posttreatment imaging demonstrated intrafractional variations of 0.15 cm (RMS). The individual shifts in three standard orthogonal planes showed no obvious directional biases.


CONCLUSIONS
After localization based on superficial markings in patients undergoing SBRT, orthogonal kV imaging detects setup variations of approximately 3 to 4 mm in each direction. Cone-beam CT detects residual setup variations of approximately 2 to 3 mm.
Wang
Zhiheng
Z
Department of Radiation Oncology, Duke University Medical Center, Durham, NC, USA.
Nelson
John W
JW
Yoo
Sua
S
Wu
Q Jackie
QJ
Kirkpatrick
John P
JP
Marks
Lawrence B
LB
Yin
Fang-Fang
FF
D054893:Cone-Beam Computed Tomography / Q000379:methods* / Q000592:standards; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging / Q000601:surgery; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods