A Study On The Strategies Of Optimizing CT Radiation Protection In Guangdong Province

Research Background and SignificanceComputed Tomography, or CT, refers to the reconstruction of tomography image a measured object, using computer technology, to obtain3D scanning tomographic images. The scan is based on a single axial plane of the ray running through the measured object. Based on the different ray absorption and transmittance of various parts of the measured object, computer collects the ray that come through and reconstructs a three-dimensional image.CT is featured by a high resolution image and the absence of overlapping images, and it plays an increasingly important role in body check and early diagnosis of diseases. CT makes a great contribution to the clinical diagnosis of specific diseases, but it also increases the radiation dose of subjects. United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR, reported in Sources and effects of ionizing radiation. Vol. I:Sources, Vol.:Effects,2000.8-10, that the CT examination is the main reason for increase in radiation dose; its share accounted for34%of the medical radiation dose. Therefore, the Ministry of Health requires the local health administrative departments to strengthen supervision of medical institutions to carry out the work of radiology. The medical institutions shall abide by the principle of justified amount of radioactive exposure and optimization of radiological protection. Diagnostic radiology examination should weight the advantages and disadvantages to ensure the diagnosis effect. Given the diagnostic effects, the diagnostic technology with smaller effect on human health should be adopted. Exposure doses should be strictly controlled and sensitive organs and tissues of the near radiation field should be protected by shielding.Radiological protection optimization can be carried out from two aspects of the equipment and technology. As far as equipment is concerned, the technical specifications and the performance of the safety of the radiology equipments and related equipments shall comply with the relevant standards and requirements. After the installation, repair or replacement of important parts of the equipment, it shall be examined by qualification testing organizations, approved by the provincial-level (or above) health administrative departments. Upon the compliance of the examination and qualify assured, the equipment could be deployed. In terms of technology, we should improve our radiography technology, in order to reasonably reduce patient exposure doses. Lungs, sinuses, bone tissue and other high-contrast tissues, during the CT scan, could be examined in this way:keep the tube voltage constant, lower tube current low-dose. This CT scan has little impact on the image quality, and thus the impact on the clinical value is also smaller. Therefore, in recent years, low-dose lung scanning technology has been increasingly adopted in clinical practice, which is widely reported in the literature. But how much is the X-ray dose in the Low-dose X-ray CT scan? How much is the reduction compared with the conventional-dose scan? How much did it impact on the adjacent tissues? These questions remain unanswered. This research adopts the imported human body model, and try to answer the above-mentioned questions. This research studies the dose of the body’s major organs subject to X-slice CT and compare its dose with the conventional CT doses. It scientifically and objectively points out that multi-slice low-dose CT scanning, on the basis of access to high-quality images, is able to reduce the exposure doses of patients’ major organs. The study helps promote the use of low-dose CT scanning technique in clinical practice by providing evidence for the health sector to develop new national standards on the inspection and testing of the CT images.Objective:To study the different doses of low-dose CT scan and conventional CT scan in chest CT examination, and to provide evidence for radiological protection and supervision.Materials and Methods1The Survey and Analysis of the diagnostic radiology equipment applications and Radiation Protection in our Province1.1subjects and contentThree cities of Guangzhou, Zhaoqing and Chaozhou are the surveyed.16hospitals are selected (six Level-three hospitals, five Level-two hospitals and5Level-one hospital) to carry out the investigation about radiology protection. The survey includes:the status quo of X-ray diagnostic equipment safety and quality, safety control tests, and the status quo of the radiology protection. In the survey,46diagnostic radiology equipments were examined, among which there are*X-ray cameras,*X-ray fluoroscopy,*CT machine,*breast X-ray screen film camera and*CR.1.2MethodsThe methods of this investigation are on-site surveys, on-site testing of the radiology equipment safety and quality and safety control and the laboratory monitoring.1.3Results46diagnostic radiology equipments were detected.13were unqualified, which meant that the pass rate was72%. Among them, mammography and CR all failed. the overall pass rate of Level-Two and Level-three hospital equipments was over80%, and the overall pass rate of the Level-one hospital equipment was33%. Six medical institutions were not equipped with protective equipments for patients, including one Level-two hospitals and remaining five Level-one hospitals.2The dose assessment of the main organs in low-dose CT scanning2.1Instruments and equipmentsPhilips16-slice spiral CT, single-row CT (Carino,);standard human body model (U.S. ART);FJ377thermo-luminescence dosimeters (Beijing261);individual dose components for LiF (Mg, Cu, P) powder (self-filling).2.1.1U.S. ART standards body modelIn this study, the use of the ART body model to examine the CT scan dose is advanced in measurement. The model is made up of tissue-equivalent material, in line with the requirements of No.44technical report by International Committee of Radiation Units and Measurement (ICRU). Besides, the model is simple to use and the data it produces in the measurement are precise.Standard human body model consists of32layers, each of which has small holes for placing the pyroelectric photo-detector. The experiment of this study used13layers, from the10th layer to the22nd layer. Before the scanning and positioning, dose components (recommended by ICRP60Publication No.60) were inserted into the pinpointed holes in the main organs or tissues within the body model. A number of measurement points were positioned and numbered in each layer. 2.2Technical Parameters of Conventional Scanning and Low-dose ScanningGroup Ⅰ:Philips16-slice spiral CT scannerThe conventional scanning conditions:120Kv,200mAs, slice thickness:5mm, scanning parts:Chest Lung and its neighboring organs.low-dose scanning Conditions:90Kv,124mAs, slice thickness:5mm, scanning parts:Chest Lung and its neighboring organs.2.3Quality ControlGroup Ⅱ:Carino single-slice CTThe conventional scanning conditions:120Kv,300mAs, slice thickness:10mm, scanning parts:Chest Lung and its neighboring organs.Low-dose CT scanning conditions of:120Kv,135mAs, thickness:10mm, scanning parts:Chest Lung and its neighboring organs.The models, specifications and technical indicators of all the equipments are in line with national standards and pass the regular inspection by the metrology department. Individual dose components of LiF (Mg, Cu, P) powder are consistent, with a precision range of within±5%. Dose components with consistency are subject to the same scale factor. TLD dosimeters, provided by the Chinese Academy of Medical Sciences Institute of Radiation Medicine, are placed in the scanned organs where the TLD powder dosimeters are also placed, to be used as a comparison to ensure the accuracy of the data.2.4Experimental MethodsBefore the scanning, dose components are placed into the target holes in the left and right lung, sternum and liver of the body. In accordance with a set of exposure conditions, single-slice CT and16-slice CT are conducted, respectively, on the phantom scan. Then the dose components are removed, and inserted in the number plate slot, placed into the lead box and taken back to the laboratory for measurements.Powders in the TLD tube are divided into three equal parts, and read respectively. The mean of three readings multiplied by the scale factor is the actual exposure dose value.2.5Image quality judgmentCritical analysis is conducted by two physicians each with more than10years CT work experience. Without knowing the scanning parameters of the scanning (blinded method), they are required to judge the image quality of the80low-dose scan and80high-dose scan. They are supposed to mark good, fair, or poor about the image quality.2.6Statistical methodsSPSS13.0statistical software is used to process the data. The dose is represented by the mean±standard deviation. Repeated measures analysis of variance and independent sample t test are adopted. Prior to the repeated measures analysis, data are subject to spherically symmetric test. If the data are not spherically symmetric, Greenhouse-Geisser is adopted for s correction factor to correct the degrees of freedom. P<0.05is considered statistically significant.ResultA comparison of the absorbed dose in different lung points scanned.Because in Spherical test statistic W＜0.001, P<0.001, we refused spherical assumption, and adopt the ε correction factor to correct the degrees of freedom. The Greenhouse-Geisser correction coefficient is adopted. The results show the significant differences exist between different parts of the points scanned (P＜0.001). Interaction effect exists (P＜0.001) between the body parts scanned and the high and low doses of scanning. Interaction effect also exists between the dose component location and the equipment (P left lung=0.002, P right lung=0.006). A comparison of the absorbed dose in different bone marrow points scanned. Because in Spherical test statistic W＜0.001, P＜0.001, we refused spherical assumption, and adopt the ε correction factor to correct the degrees of freedom. The Greenhouse-Geisser correction coefficient is adopted. The results show the significant differences exist between different parts of the points scanned (P＜0.001). Interaction effect exists (P=0.021) between the body parts scanned and the high and low doses of scanning. Interaction effect also exists between the dose component location and the equipment (P=0.005).A comparison of the absorbed dose in different lower-lung points scanned.Because in Spherical test statistic W＜0.001, P＜0.001, we refuse spherical assumption, and adopt the ε correction factor to correct the degrees of freedom. The Greenhouse-Geisser correction coefficient is adopted. The results show the significant differences exist between different parts of the points scanned (P＜0.001). The lower-liver dose exposure was significantly reduced. Interaction effect does not exist (P=0.086) between the body parts scanned and the high and low doses of scanning. Interaction effect exists between the dose component location and the equipment (P=0.02).Image qualityThe image quality of low-dose scan all met the diagnostic requirements. A double-blind judgment by the two physicians shows that the images are all of the good or fair quality, which meet the diagnostic requirements.ConclusionIn the medical institutions of our province, the radiology protection situation is worrying. There are some salient issues. For example, the annual radiology equipment protection and quality control detection rate is not high; the devices failed in re-examination; personal protective equipment is not readily equipped or improperly applied. In the grass-root level, the radiological protection is particularly unqualified and in a serious non-compliance situation. The overall pass rate in Level-one hospital was merely33%. The radiological health regulation is not fully in place.Both single-slice CT and16-slice CT, with reasonable scanning parameters, can produce low dose scanning, which produces the desired image quality required in diagnostic.In the low-dose scanning of single-slice CT or16-slice CT scan, patients are subject to significantly lower exposure than in the conventional scanning method, which is worthy of clinical practice.In single-slice CT, the dose of low-dose scan is about half of the conventional scanning method. In16-slice CT, the dose of low-dose scan is about one-third of the conventional scanning method. Therefore, in16-slice CT scans, low-dose scan enable patients to be more protective.In the lung CT scan, bone marrow would be subject to inevitable exposure. Besides, adjacent organs such as the liver would also be fairly exposed, and its biological effects need further study.Radiation Health regulatory authorities should strengthen supervision and inspection on the work of radiology. They should stipulate that given the ensured image quality, the CT scan dose should be reasonably reduced, so as to promote the low-dose scanning. This will reduce the exposed dose of the subjects from the source. They should also stipulate that radiology unit is equipped with a sufficient number of radiological protection products, which are properly deployed in the radiology activities in order to reduce the exposure doses of sensitive organs and tissues, adjacent to the radiation field. The health sector should also develop a new CT operating standards and testing specifications, system and technical specifications to ensure the safety of medical exposure in a CT examination.