Respiratory gating during stereotactic body radiotherapy for lung cancer reduces tumor position variability.
OBJECTIVE
We evaluated the effects of respiratory gating on treatment accuracy in lung cancer patients undergoing lung stereotactic body radiotherapy by using electronic portal imaging device (EPID) images.


METHODS
Our study population consisted of 30 lung cancer patients treated with stereotactic body radiotherapy (48 Gy/4 fractions/4 to 9 days). Of these, 14 were treated with- (group A) and 16 without gating (group B); typically the patients whose tumors showed three-dimensional respiratory motion ≧5 mm were selected for gating. Tumor respiratory motion was estimated using four-dimensional computed tomography images acquired during treatment simulation. Tumor position variability during all treatment sessions was assessed by measuring the standard deviation (SD) and range of tumor displacement on EPID images. The two groups were compared for tumor respiratory motion and position variability using the Mann-Whitney U test.


RESULTS
The median three-dimensional tumor motion during simulation was greater in group A than group B (9 mm, range 3-30 mm vs. 2 mm, range 0-4 mm; p<0.001). In groups A and B the median SD of the tumor position was 1.1 mm and 0.9 mm in the craniocaudal- (p = 0.24) and 0.7 mm and 0.6 mm in the mediolateral direction (p = 0.89), respectively. The median range of the tumor position was 4.0 mm and 3.0 mm in the craniocaudal- (p = 0.21) and 2.0 mm and 1.5 mm in the mediolateral direction (p = 0.20), respectively.


CONCLUSIONS
Although patients treated with respiratory gating exhibited greater respiratory tumor motion during treatment simulation, tumor position variability in the EPID images was low and comparable to patients treated without gating. This demonstrates the benefit of respiratory gating.
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Tetsuo
T
Saito
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Tomohiko
T
Matsuyama
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Ryo
R
Toya
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Yoshiyuki
Y
Fukugawa
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Takamasa
T
Toyofuku
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Akiko
A
Semba
Department of Radiation Oncology, Kumamoto University Hospital, Kumamoto, Japan.
Natsuo
N
Oya
D056973:Four-Dimensional Computed Tomography / Q000379:methods; D006801:Humans; D008168:Lung / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008175:Lung Neoplasms / Q000503:physiopathology / Q000601:surgery*; D015588:Observer Variation; D016634:Radiosurgery / Q000379:methods*; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D012143:Respiratory Physiological Phenomena