The Verification Method of Deposite Dose Area with Positrons for External Photon Radiotherapy

在癌症治疗的高能X射线照射期间，还没有确定的方法可用于实时测量患者体内的处方剂量。我们提出了一种新的利用正电子产生的PEV方法。本研究就是为了实现这一方法。以下是研究结果的总结：(1)高能X射线是光子。光子可以产生一对电子和正电子。我们得出了生产点的分布与受照面积相对应的思想，并从理论上对这一思想进行了研究。用Geant4程序模拟计算的结果表明，在照射区域内产生了大量的电子-正电子对，每个正电子与体内的电子结合，湮没成光子。(2)在放疗室内发现了极高的背景。我们利用自制的无机闪烁(YAP(Ce))传感器组成了一个望远镜，成功地探测到了湮没光子。(3)通过定义带有准直器的望远镜的视角，我们可以测量出受照射区域的大小，位置分辨率约为1 mm。(4)作为本研究的结果，我们可以利用所提出的PEV方法来实时监测X射线照射过程中受照射区域的剂量分布。我们在实时监测该区域方面取得的成功远远领先于甚至在全球范围内的研究成果。作为未来的计划，我们建议制造一台带有100个传感器的PEV相机用于临床。实时处理来自摄像机的信号将有可能在放射肿瘤学家的显示器上显示结果，这将避免不幸的漏照射。

No established method is available for real-time measurements of prescribed dose in the patient body during high-energy X-ray beam irradiation in cancer therapy. We proposed a novel PEV method that utilizes positron production. This research is to realize the method. Here is the summary of the results.(1) High-energy X-rays are photons. The photon can produce a pair of electron and positron. We reached to an idea that the distribution of production points corresponds to the irradiated area, and theoretically studied the idea. The results of simulation calculations with the Geant4 code showed that many number of electron-positron pairs were produced and each of the positrons were combined with electrons in the body to annihilate into to photons in the irradiated area.(2) We found an extremely high background in the radiotherapy room. We managed the circumstance by using the originally fabricated sensors with inorganic scintillation (YAP(Ce)) to form a telescope, and detected annihilation photons successfully.(3) We could measure the size of irradiated area with the position resolution of about 1mm by defining the view of the telescope with collimators.(4) As the result of this research, we conclude that one can carry out real-time monitoring of the irradiated area for dose delivery during X-ray irradiation with the proposed PEV method.Our success obtained in this research in the real-time monitoring of the area is far ahead to the achievements for the purpose even in the scope of the whole world. As a future plan, we recommend to make a PEV camera with one hundred sensors for the clinical use. Real-time processing of the signals from the camera will make possible to show the result on the display for radiation oncologist, and this will avoid unfortunate miss-irradiation.