The real-time tumor-tracking radiotherapy system includes two sets of fluoroscopes that detect the fiducial markers in or near the tumor constantly during radiotherapy. The treatment beam is irradiated to the tumor only when fiducial markers are located in the target position. Treatment time is extended in case of large respiratory tumor motion. A high-power fluoroscopic X-ray is required in the case of fiducial markers in parenchymal organs with heavy X-ray attenuation. It was a concern that radiodermatitis was caused by an increasing entrance skin dose from the fluoroscopic X-ray. In order to estimate the entrance skin dose from the fluoroscopic X-ray, we measured the entrance skin dose rate through the use of a method recommended by the Japanese Society of Radiological Technology. We applied sine wave simulation to resemble the respiratory motion of the tumor. In conclusion, we confirm that entrance skin dose from fluoroscopy during RTRT is lower than the threshold dose for radiodermatitis.
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