Institut de Física Corpuscular (IFIC), CSIC-UV, València, Spain.
Phys Med Biol. 2023 Jul 5;68(14). doi: 10.1088/1361-6560/ace024.
. Background events are one of the most relevant contributions to image degradation in Compton camera imaging for hadron therapy treatment monitoring. A study of the background and its contribution to image degradation is important to define future strategies to reduce the background in the system.. In this simulation study, the percentage of different kinds of events and their contribution to the reconstructed image in a two-layer Compton camera have been evaluated. To this end, GATE v8.2 simulations of a proton beam impinging on a PMMA phantom have been carried out, for different proton beam energies and at different beam intensities.. For a simulated Compton camera made of Lanthanum (III) Bromide monolithic crystals, coincidences caused by neutrons arriving from the phantom are the most common type of background produced by secondary radiations in the Compton camera, causing between 13% and 33% of the detected coincidences, depending on the beam energy. Results also show that random coincidences are a significant cause of image degradation at high beam intensities, and their influence in the reconstructed images is studied for values of the time coincidence windows from 500 ps to 100 ns.. Results indicate the timing capabilities required to retrieve the fall-off position with good precision. Still, the noise observed in the image when no randoms are considered make us consider further background rejection methods.
背景事件是康普顿相机成像中导致图像退化的最主要因素之一，对于强子治疗监测用康普顿相机成像而言，研究背景及其对图像退化的贡献非常重要，这有助于确定未来减少系统背景的策略。
在这项模拟研究中，评估了两层康普顿相机中不同类型事件的比例及其对重建图像的贡献。为此，针对不同质子束能量和不同束流强度，利用 GATE v8.2 对质子束撞击 PMMA 体模进行了模拟。
对于由镧（III）溴化物整体晶体制成的模拟康普顿相机，来自体模的中子引发的符合事件是康普顿相机中次级辐射产生的最常见的背景类型，其造成的符合事件约占总符合事件的 13%至 33%，具体取决于束流能量。结果还表明，在高束流强度下，随机符合事件是图像退化的一个重要原因，研究了时间符合窗口为 500 ps 到 100 ns 时对重建图像的影响。
结果表明，为了精确地恢复下降位置，需要具备一定的定时能力。然而，当不考虑随机事件时，图像中观察到的噪声使我们考虑进一步的背景抑制方法。
