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

在癌症治疗的高能x射线照射过程中，没有既定的方法可以实时测量患者体内的规定剂量。我们提出了一种利用正电子产生的新型PEV方法。本文的研究就是要实现这种方法。以下是调查结果的摘要。高能x射线是光子。光子能产生一对电子和正电子。我们得出了生产点的分布与辐照面积相对应的观点，并对这一观点进行了理论研究。用Geant4代码模拟计算的结果表明，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，在辐照区域湮灭为光子。我们发现放射治疗室的背景辐射非常高。我们利用自制的无机闪烁传感器（YAP(Ce)）组成望远镜，成功探测到湮灭光子。(3)通过用准直器定义望远镜的视场，可以测量出辐照区域的大小，位置分辨率约为1mm。(4)本研究结果表明，采用本文提出的PEV方法可以实时监测x射线照射过程中照射区域的剂量传递情况。我们在本研究中所取得的成功，在该领域的实时监测方面，甚至在全世界范围内取得的成果都是遥遥领先的。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。实时处理来自摄像机的信号将有可能在显示器上显示放射肿瘤学家的结果，这将避免不幸的误照射。

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.