Simple quality assurance method of dynamic tumor tracking with the gimbaled linac system using a light field.
We proposed a simple visual method for evaluating the dynamic tumor tracking (DTT) accuracy of a gimbal mechanism using a light field. A single photon beam was set with a field size of 30 × 30 mm2 at a gantry angle of 90°. The center of a cube phantom was set up at the isocenter of a motion table, and 4D modeling was performed based on the tumor and infrared (IR) marker motion. After 4D modeling, the cube phantom was replaced with a sheet of paper, which was placed perpen-dicularly, and a light field was projected on the sheet of paper. The light field was recorded using a web camera in a treatment room that was as dark as possible. Calculated images from each image obtained using the camera were summed to compose a total summation image. Sinusoidal motion sequences were produced by moving the phantom with a fixed amplitude of 20 mm and different breathing periods of 2, 4, 6, and 8 s. The light field was projected on the sheet of paper under three conditions: with the moving phantom and DTT based on the motion of the phantom, with the moving phantom and non-DTT, and with a stationary phantom for comparison. The values of tracking errors using the light field were 1.12 ± 0.72, 0.31 ± 0.19, 0.27 ± 0.12, and 0.15 ± 0.09 mm for breathing periods of 2, 4, 6, and 8s, respectively. The tracking accuracy showed dependence on the breath-ing period. We proposed a simple quality assurance (QA) process for the tracking accuracy of a gimbal mechanism system using a light field and web camera. Our method can assess the tracking accuracy using a light field without irradiation and clearly visualize distributions like film dosimetry.
Hiroshima High-Precision Radiotherapy Cancer Center. miura@hiprac.jp.
Hideharu
H
Miura
Shuichi
S
Ozawa
Masahiro
M
Hayata
Shintaro
S
Tsuda
Kiyoshi
K
Yamada
Yasushi
Y
Nagata
D006801:Humans; D009068:Movement; D009369:Neoplasms / Q000532:radiotherapy*; D010315:Particle Accelerators / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care / Q000592:standards*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000592:standards*
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