Abstract
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 perpendicularly, 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 8 s, respectively. The tracking accuracy showed dependence on the breathing 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.PACS number(s): 87.56 Fc, 87.55.Qr
Highlights
178 Miura et al.: Verification of infrared tracking using a light fieldsurrogates or an internally implanted marker
An overview of the management of respiratory motion in radiotherapy was summarized in the report of the American Association of Physicists in Medicine (AAPM) Task Group (TG) 76.(1)
Several investigators reported a high tracking accuracy of dynamic tumor tracking (DTT) through the Vero4DRT system using chamber and film measurements, even for rapidly moving patterns.[6,7,8] Indirect DTT using the Vero4DRT system using the gimbal reduced the blurring effect of respiratory motion with high accuracy
Summary
178 Miura et al.: Verification of infrared tracking using a light fieldsurrogates (indirect DTT) or an internally implanted marker (direct DTT). The accuracy of indirect DTT should be verified by the model predicting the internal target position based on surrogate measurements before clinical use. Several investigators reported a high tracking accuracy of DTT through the Vero4DRT system using chamber and film measurements, even for rapidly moving patterns.[6,7,8] Indirect DTT using the Vero4DRT system using the gimbal reduced the blurring effect of respiratory motion with high accuracy. The accuracy of the model predicting the internal target position based on surrogate measurement, verification of the gimbal mechanism, and patient dose verification QA, is important. AAPM-TG report 40/142 recommends testing the radiation and light field agreement on a monthly basis with a tolerance of 2 mm or 1% on any side.[11,12] Here, we propose a simple visual method for evaluating the DTT accuracy of the gimbal mechanism using a light field
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