Feasibility Study on Imaging of Scattered High-Energy Photons for Detecting Changes in Void Size
Abstract
In external beam radiation therapy, it is crucial to deliver adequate radiation dose to the tumor while minimizing radiation exposure to surrounding normal tissues. However, the internal tissues within the human body constantly change their position due to breathing and cardiac pulsation, making it important to monitor tumor position externally during exposure. There are no established methods for detecting position changes of the tumor non-invasively caused especially by the movement of internal cavities (such as gas in the intestines) within the body. Therefore, this study investigated whether it is possible to monitor the behavior of internal cavities located between the tumor and a gamma camera by capturing the scattered high-energy X-rays emitted during radiation therapy. A 20 cm square acrylic block was irradiated by a beam of gamma rays from a Co-60 source that was collimated into a square column shape. A void was set at the position where direct gamma rays were not irradiated. Scattered gamma rays passing through the void were captured using a gamma camera consisting of a pinhole collimator and a phosphor plate. An increase in the amount of scattered gamma rays in the captured images was observed when the size of the void was changed from 1 cm square to 3 cm square. Experiments were also carried out with scattered gamma ray with angles of 45 degrees, 90 degrees, and 135 degrees relative to the incident gamma ray beam. The experimental results confirmed that the…
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