Measurement of interfraction variations in position and size of target volumes in stereotactic body radiotherapy for lung cancer.
OBJECTIVE
To investigate the interfraction variations in volume, motion range, and position of the gross tumor volume (GTV) in hypofractionated stereotactic body radiotherapy (SBRT) for lung cancer using four-dimensional computed tomography.


METHODS
Four-dimensional computed tomography scans were acquired for 8 patients once at treatment planning and twice during the SBRT period using a stereotactic body frame. The image registration was performed to correct setup errors for clinical four-dimensional computed tomography. The interfraction variations in volume, motion range, and position of GTV were computed at end-inhalation (EI) and end-exhalation (EE).


RESULTS
The random variations in the GTV were 0.59 cm(3) at EI and 0.53 cm(3) at EE, and the systematic variations were 3.04 cm(3) at EI and 3.21 cm(3) at EE. No significant variations in GTV were found during the SBRT sessions (p = .301 at EI and p = .081 at EE). The random variations in GTV motion range for the upper lobe in the craniocaudal direction were within 1.0 mm and for the lower lobe was 3.4 mm. The interfraction variations in the GTV centroid position in the anteroposterior and craniocaudal directions were mostly larger than in the right-left direction; however, no significant displacement was observed among the sessions in any direction.


CONCLUSIONS
For patients undergoing hypofractionated SBRT, interfraction variations in GTV, motion range, and position mainly remained small. An additional approach is needed to assess the margin size.
Matsugi
Kiyotomo
K
Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Narita
Yuichiro
Y
Sawada
Akira
A
Nakamura
Mitsuhiro
M
Miyabe
Yuki
Y
Matsuo
Yukinori
Y
Narabayashi
Masaru
M
Norihisa
Yoshiki
Y
Mizowaki
Takashi
T
Hiraoka
Masahiro
M
D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D019583:Dose Fractionation, Radiation; D045853:Exhalation; D005260:Female; D006801:Humans; D001239:Inhalation; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009068:Movement; D019047:Phantoms, Imaging; D016634:Radiosurgery / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden