Detection of lung tumor movement in real-time tumor-tracking radiotherapy.
OBJECTIVE
External radiotherapy for lung tumors requires reducing the uncertainty due to setup error and organ motion. We investigated the three-dimensional movement of lung tumors through an inserted internal marker using a real-time tumor-tracking system and evaluated the efficacy of this system at reducing the internal margin.


METHODS
Four patients with lung cancer were analyzed. A 2.0-mm gold marker was inserted into the tumor. The real-time tumor-tracking system calculates and stores three-dimensional coordinates of the marker 30 times/s. The system can trigger the linear accelerator to irradiate the tumor only when the marker is located within the predetermined "permitted dislocation." The value was set at +/-1 to +/-3 mm according to the patient's characteristics. We analyzed 10,413-14,893 data sets for each of the 4 patients. The range of marker movement during normal breathing (beam-off period) was compared with that during gated irradiation (beam-on period) by Student's t test.


RESULTS
The range of marker movement during the beam-off period was 5.5-10.0 mm in the lateral direction (x), 6.8-15.9 mm in the craniocaudal direction (y) and 8.1-14.6 mm in the ventrodorsal direction (z). The range during the beam-on period was reduced to within 5.3 mm in all directions in all 4 patients. A significant difference was found between the mean of the range during the beam-off period and the mean of the range during the beam-on period in the x (p = 0.007), y (p = 0.025), and z (p = 0.002) coordinates, respectively.


CONCLUSIONS
The real-time tumor-tracking radiotherapy system was useful to analyze the movement of an internal marker. Treatment with megavoltage X-rays was properly given when the tumor marker moved into the "permitted dislocation" zone from the planned position.
Shimizu
S
S
Department of Radiation Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
Shirato
H
H
Ogura
S
S
Akita-Dosaka
H
H
Kitamura
K
K
Nishioka
T
T
Kagei
K
K
Nishimura
M
M
Miyasaka
K
K
D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003199:Computer Systems; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008875:Middle Aged; D009068:Movement; D010315:Particle Accelerators; D020266:Radiotherapy, Conformal / Q000379:methods; D014057:Tomography, X-Ray Computed