Translational and rotational localization errors in cone-beam CT based image-guided lung stereotactic radiotherapy.
OBJECTIVE
Accurate localization is crucial in delivering safe and effective stereotactic body radiation therapy (SBRT). The aim of this study was to analyse the accuracy of image-guidance using the cone-beam computed tomography (CBCT) of the VERO system in 57 patients treated for lung SBRT and to calculate the treatment margins.


METHODS
The internal target volume (ITV) was obtained by contouring the tumor on maximum and mean intensity projection CT images reconstructed from a respiration correlated 4D-CT. Translational and rotational tumor localization errors were identified by comparing the manual registration of the ITV to the motion-blurred tumor on the CBCT and they were corrected by means of the robotic couch and the ring rotation. A verification CBCT was acquired after correction in order to evaluate residual errors.


RESULTS
The mean 3D vector at initial set-up was 6.6±2.3mm, which was significantly reduced to 1.6±0.8mm after 6D automatic correction. 94% of the rotational errors were within 3°. The PTV margins used to compensate for residual tumor localization errors were 3.1, 3.5 and 3.3mm in the LR, SI and AP directions, respectively.


CONCLUSIONS
On-line image guidance with the ITV-CBCT matching technique and automatic 6D correction of the VERO system allowed a very accurate tumor localization in lung SBRT.
Unit of Radiation Research, European Institute of Oncology, Milano, Italy. Electronic address: cristina.garibaldi@ieo.it.
Cristina
C
Garibaldi
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Gaia
G
Piperno
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Annamaria
A
Ferrari
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Alessia
A
Surgo
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Matteo
M
Muto
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy.
Sara
S
Ronchi
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Alessia
A
Bazani
Unit of Medical Physics, European Institute of Oncology, Milano, Italy.
Floriana
F
Pansini
Unit of Radiation Research, European Institute of Oncology, Milano, Italy.
Marta
M
Cremonesi
Department of Radiation Oncology, European Institute of Oncology, Milano, Italy; Department of Health Sciences, Università degli Studi di Milano, Milano, Italy.
Barbara Alicja
BA
Jereczek-Fossa
Department of Health Sciences, Università degli Studi di Milano, Milano, Italy; Scientific Director, European Institute of Oncology, Milano, Italy.
Roberto
R
Orecchia
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted; D061106:Radiotherapy Setup Errors; D061089:Radiotherapy, Image-Guided; D012399:Rotation
Image-guided radiotherapy; Lung SBRT; Translational and rotational localization error