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

在癌症治疗的高能X射线束照射期间，没有建立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PEV方法，利用正电子生产。本研究就是为了实现该方法。以下是结果的摘要。(1)高能X射线是光子。光子能产生一对电子和正电子。提出了生产点的分布与照射面积相对应的思想，并从理论上对这一思想进行了研究。用Geant 4程序模拟计算结果表明，在辐照区产生了大量的电子-正电子对，每个正电子在体内与电子结合湮灭成光子。(2)我们在放射治疗室发现了一个非常高的背景。我们利用原先制作的无机闪烁（雅普（Ce））传感器组成望远镜，成功地探测到了湮没光子。(3)利用准直器确定望远镜的视场，可以测量出位置分辨率约为1 mm的照射面积大小。(4)研究结果表明，利用PEV方法可以对X射线辐照过程中的剂量传递进行实时监测，我们在该领域的实时监测方面所取得的成就在国际上也是遥遥领先的。作为未来的计划，我们建议制作一个具有100个传感器的PEV相机用于临床使用。实时处理来自摄像机的信号，将有可能显示在显示器上的放射肿瘤学家的结果，这将避免不幸的错过照射。

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.