Positron emission tomography imaging of large medical equipment / X-ray tomography (Positron Emission Tomography /Computed Tomography, PET/CT) application, more and more people begin to contact and accept PET/CT detection and cancer screening, even for health check. With the media of a nuclear accident or foreign military knowledge, to accept public radiation safety knowledge more, and also focus on other portrait ray, began to realize the radiation problem of PET/CT examination, raises questions about the radiation safety of PET/CT examination, PET/CT examination "really safe? How long two inspection interval good time?" Such problems become the most important consulting questions that are ready to be checked, and even fear. PET/CT in China started in 2002, with the PET/CT equipment unceasing renewal, the nuclide dose using the PET more and more small, CT scan faster, radiation dose control is getting better, it must recognize the PET/CT examination and PET/CT examination of radiation safety.

       Radiation dose source PET/CT in the two part, radionuclide and X-CT, radiation PET most of the sources of fluoride in -18 (18F), 18F positron emission, high-energy gamma rays, some radiation on the human body, the radiation dose is about 2.1 * 10-2mSv/MBq, a general check using 222 ~ 296 MBq. The patients received a PET/CT scan, PET scan which required radiation dose of radionuclides produced about 4.6 ~ 6.2 mSv, but with the upgrading of equipment, the third generation of PET/CT products, radionuclide doses can be reduced to about 185 MBq, the radiation dose decreased to about 3.8mSv. The radiopharmaceuticals used are analogues of physiological metabolites, such as 18F-FDG commonly used as glucose analogues, which are not allergenic, and are harmless to human body. The radioactive nuclide is an isotope of an ultra short half-life, which decays quickly and is completely removed from the body within a few hours. By drinking more water and accelerating the excretion of drugs, the total dose of radionuclide radiation in patients can also be reduced.

       The radiation dose of the PET/CT was mainly derived from the CT scan, but the CT used by PET/CT was lower than that of the conventional CT. The Japanese Medical Association investigated the average radiation dose of CT by X-ray CT at 10.1 + 7.85 mSv when the body tumor health examination was investigated. The greater the radiation dose past old generation CT produced, generally in the 18mSv above, and the CT scan PET/CT is generally used in lower power flow collection, radiation dose to radiation dose in conventional CT scanning of 1/2, University of Hong Kong. The study results showed that the effective radiation dose PET/CT examination in CT were 7.22mSv and 7.42mSv on women and men. However, with the update of PET/CT, PET/CT is also equipped with a more advanced CT, the scanning time is shortened, and the radiation dose will also be significantly reduced. The radiation dose of a whole body examination of PET/CT was reduced from about 15mSv to about 7.5mSv (7 ~ 10.2). But if the use of high Ma scanning mode or enhanced scan mode, CT dose can be as high as 14.1 ~ 18.6mSv, so the PET/CT scan dose increase mainly depends on the CT scan mode, conventional CT scanning PET/CT imaging in general recommended low dose (low MA) scan mode, then the local organs suspected by diagnostic dose try to reduce the radiation dose, the subjects of the.

       After all, PET/CT examination has certain radiation dose, and other medical examination and treatment, such as medicine, can cure the disease, but also have certain side effects, when used to weigh the pros and cons of such as surgery can be effective treatment; and disease, but may also bring some tissues and organs of the structure or function of the injury. Therefore, any medical behavior should be benefit from patients, that is to find the best node in cost benefit, strictly grasp the indication of PET/CT inspection, and use the PET/CT inspection based on the principle of justification and optimization, so that the benefit of the examinees is obviously greater than the risk.

       For the active prevention of tumors, early detection of early treatment, 70% of malignant tumors can be avoided, 90% can be cured. A survey in the United States showed that 87% of the respondents approved the regular cancer screening, and 68% of the women thought that screening could prevent or reduce the risk of breast cancer. The National Cancer Association of the United States estimates that 30% to 35% of cancer patients can be prevented from premature death by proper screening. The screening data for lung cancer showed that 80% of the lung positive results of PET/CT imaging were stage I of lung cancer. Because PET/CT improves the accuracy of early diagnosis, staging and identification of benign and malignant nodules, PET/CT is probably the best method for early diagnosis of lung cancer and even whole body tumors. Some scholars also showed that the median survival time of patients with non-small cell lung cancer who received radical radiotherapy or chemotherapy before treatment was 18F- FDG PET and the median survival time was almost twice that.

       PET/CT in the diagnosis and differential diagnosis of tumor; tumor staging and re staging, degree of differentiation; differentiating tumor recurrence; tumor therapy guidance; evaluating therapeutic effect; assess the prognosis of the tumor; blood tumor markers for such compounds increased continuously, tumor tumor family of high risk patients with primary and metastatic tumor focus, and diagnosis and treatment of neuropsychiatric disorders, cardiovascular disease assessment, the subjects can get more benefit. Although PET/CT examination has a certain radiation, the benefit of PET/CT examination for patients with indications is significantly greater than that of radiation risk, and even the chance to save lives. For checking suspicious patients or changing the condition of patients, it can be determined according to the needs of disease and treatment decisions.