Daily alignment results of in-room computed tomography-guided stereotactic body radiation therapy for lung cancer.
OBJECTIVE
To determine the extent of interfractional setup errors and day-to-day organ motion errors by assessing daily bone alignment results and changes in soft tissue tumor position during hypofractionated, in-room computed tomography (CT)-guided stereotactic body radiation therapy (SBRT) of lung cancer.


METHODS
Daily alignment results during SBRT were analyzed for 117 tumors in 112 patients. Patients received 40-50 Gy of SBRT in four to five fractions using an integrated CT-LINAC system. The free-breathing CT scans acquired during treatment setup were retrospectively realigned to match with each of the bony references and the gross tumor volume (GTV) defined on the reference CT by rigid-body registration, and the daily deviations were calculated.


RESULTS
The mean magnitude (± SD) three-dimensional shift from the initial skin marks to the final bone-aligned positions was 9.4 ± 5.7 mm. The mean daily GTV deviation from the bone position was 0.1 ± 3.8 mm in the anterior-posterior direction, -0.01 ± 4.2 mm in the superior-inferior direction, and 0.2 ± 2.5 mm in the lateral direction. A clinically noteworthy trend (net change >5 mm in any direction) in GTV position relative to the bone was observed in 23 cases (20%).


CONCLUSIONS
Soft tissue target position can change significantly beyond the motion envelope defined in the original internal target volume in four-dimensional CT-based treatment planning for SBRT of lung cancer. Additional margin should be considered for adequate coverage of interfractional changes.
Ikushima
Hitoshi
H
Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Balter
Peter
P
Komaki
Ritsuko
R
Hunjun
Sandeep
S
Bucci
M Kara
MK
Liao
Zhongxing
Z
McAleer
Mary F
MF
Yu
Zhiqian H
ZH
Zhang
Yongbin
Y
Chang
Joe Y
JY
Dong
Lei
L
D001842:Bone and Bones / Q000000981:diagnostic imaging; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D009068:Movement; D016634:Radiosurgery / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden