Development of a z-axis tilting technique using a chest phantom to reduce radiation exposure during computed tomography coronary angiography.

Japan has the highest estimated exposure frequency of diagnostic X-rays in the world. Furthermore, the volumetric computed tomography dose index (CTDIvol) and dose length product (DLP) of computed tomography coronary angiography are relatively high in Japanese diagnostic reference levels, and it is important to reduce both dose indices. This study proposed a new exposure reduction technique, the vanishing liver position (VLP), where the body is tilted to the right in the z-axis. The VLP advantages include reduction in the scanning range and overlap between the heart and the liver. Three different electrocardiogram protocols were employed, and changes in the tube current in the z-axis were measured during each protocol. Additionally, changes in the radiation exposure caused by z-axis tilting were evaluated. Our results indicate that this technique reduced CTDIvol and DLP by 6.2 and 8.9%, respectively, at most, indicating that this technique can reduce radiation exposure.

SIMPLE METHOD OF MEASURING SSDE FOR HEAD CT: FACILITATING PRE-CT SCAN DOSE CALCULATION USING SPECIALIZED HEAD SCAN BAND.

In this study, scaled scan band was developed to provide size-specific dose estimation (SSDE) values based on head circumference of patients undergoing computed tomography (CT) scans. The scan band was tested in 40 consecutive head CT examinations. The accuracy of the specialized scan band method was determined by comparing SSDEband with SSDE293,forehead, SSDEmean and SSDEcenter. SSDE293,forehead was used as the control value. The results of the linear fit of SSDEband, SSDEmean and SSDEcenter against SSDE293, forehead, were R2 = 0.958, R2 = 0.984 and R2 = 0.936, respectively. There was no significant difference between SSDEband, SSDEmean and SSDEcenter for SSDE293,forehead. Use of the proposed scan band method makes it possible to accurately determine the required radiation dose before a CT examination is performed.

DEVELOPMENT OF A SPECIALISED TAPE MEASURE TO ESTIMATE THE SIZE-SPECIFIC DOSE ESTIMATE.

The risk in computed tomography (CT) examinations is radiation exposure. We aimed to develop a specialised tape measure for determining the size-specific dose estimate (SSDE) for patients undergoing CT scans. The scanning parameters used were those of the abdominal protocol in our institute. With this method, the SSDE220 and standard deviations obtained from CT images for the liver, pelvic and lung areas, corresponded closely to the SSDEtape and standard deviations obtained using the tape measure. We thus devised a new idea that allows the estimation of the SSDE220 using a specialised tape measure before the CT examination, allowing for an informed explanation of the radiation dose to the patient. Although the tape measure developed in this study is specific to one particular CT instrument, the method could be adapted to a wide range of radiography applications.

[Clinical Preparations: Status Quo and Challenges in the Future].

Dispensing clinical preparations requires the professional ability of pharmacists as specialists who understand the physicochemical properties of drugs. Clinical preparations contribute to the support of drug therapy and to commercialization by pharmaceutical companies. The Japanese Society of Hospital Pharmacists published the Guidelines on Hospital Preparations and Use in 2012. Those guidelines were designed to improve the safety and utility of hospital preparations, indicate the standard procedures for treatment in hospitals, and show how to ensure the quality of hospital preparations. The expiration dates for clinical preparations should be determined, although this is not done for most because of the numerous hospitals and differences in their approaches to quality control. Furthermore, the acquisition of informed consent for the use of clinical preparations is inadequate. After the guidelines were released, some problems have occurred, such as the underfilling of prescriptions for progesterone vaginal suppositories and overdoses of selenium injections. It therefore appears necessary to consider the development of a new procedural manual on clinical preparations. In this symposium, I discuss relief or safety measures for clinical preparations.

DEVELOPMENT OF RADIATION DOSE CALCULATION SOFTWARE USING THE SIZE-SPECIFIC DOSE ESTIMATE.

We aimed to develop a software for facilitating absorbed dose per pixel (pixel dose) calculation using a size-specific dose estimate (SSDE). We calculated the pixel dose at nine equal points inserted into the radiophotoluminescence glass dosemeter (RPLD) and compared the pixel dose with the measured doses using RPLD. With this method, the relative errors of average pixel dose was -0.1% for adults and 2.86, 3.36 and 1.17% for those aged 10, 5 and 1 years without tube current modulation, respectively. In contrast, the relative error of SSDE was 17.37% for adults and 20.38, 20.73 and 19.20% for those aged 10, 5 and 1 years, respectively. In other words, the pixel dose was almost equal to the measured doses. Therefore, our software can be useful for determining arbitrary point.

A new shielding calculation method for X-ray computed tomography regarding scattered radiation.

The goal of this study is to develop a more appropriate shielding calculation method for computed tomography (CT) in comparison with the Japanese conventional (JC) method and the National Council on Radiation Protection and Measurements (NCRP)-dose length product (DLP) method. Scattered dose distributions were measured in a CT room with 18 scanners (16 scanners in the case of the JC method) for one week during routine clinical use. The radiation doses were calculated for the same period using the JC and NCRP-DLP methods. The mean (NCRP-DLP-calculated dose)/(measured dose) ratios in each direction ranged from 1.7 ± 0.6 to 55 ± 24 (mean ± standard deviation). The NCRP-DLP method underestimated the dose at 3.4% in fewer shielding directions without the gantry and a subject, and the minimum (NCRP-DLP-calculated dose)/(measured dose) ratio was 0.6. The reduction factors were 0.036 ± 0.014 and 0.24 ± 0.061 for the gantry and couch directions, respectively. The (JC-calculated dose)/(measured dose) ratios ranged from 11 ± 8.7 to 404 ± 340. The air kerma scatter factor κ is expected to be twice as high as that calculated with the NCRP-DLP method and the reduction factors are expected to be 0.1 and 0.4 for the gantry and couch directions, respectively. We, therefore, propose a more appropriate method, the Japanese-DLP method, which resolves the issues of possible underestimation of the scattered radiation and overestimation of the reduction factors in the gantry and couch directions.

Analysis of Image Gently Abdominal CT Protocol With the Use of Body Phantom Adapted to the Japanese Size.

OBJECTIVE: The purpose of this study was to analyze in detail the quality of abdominal CT images obtained using three protocols reported by Image Gently in 2014 (hereafter referred to as Image Gently 2014), with the use of a handmade body phantom adapted to typical body sizes of the Japanese population. Moreover, we converted the findings of Image Gently 2014 to match Japanese body sizes and referred to our converted findings as Image Gently Japan. MATERIALS AND METHODS: We scanned each phantom in a mechanical isocenter in accordance with the Image Gently 2014 abdominal imaging protocol. We changed the tube current-exposure time product per rotation from 25 to 250 mAs. The bowtie filter was set with a minimum FOV for the phantom size. We then analyzed the volume CT dose index (CTDIvol)-measured CT number curve. We then used this CT number curve to calculate the CT number recommended by Image Gently Japan for each of the designated patient ages. RESULTS: The CTDIvol-measured CT number curve showed that, as the CTDIvol increased with each age, image noise decreased. When we assumed that the CTDIvol value for adults was 20 mGy, the measured CT number was 12.5 HU. We then multiplied each reduction coefficient by age (neonate and 1, 5, 10, and 15 years). The measured CT numbers for Image Gently Japan performed to attain limited dose reduction were 3.0, 3.9, 4.9, 6.0, and 9.0 HU, respectively, whereas those for Image Gently Japan performed to achieve moderate dose reduction were 3.3, 4.3, 5.3, 6.3, and 9.3 HU, respectively, and those for Image Gently Japan performed to attain aggressive dose reduction were 4.1, 5.1, 5.8, 6.8, and 9.5 HU, respectively. CONCLUSION: We analyzed the abdominal image quality demanded by Image Gently 2014, and we were able to adapt the results to the Japanese population and present them as our own Image Gently Japan recommendations. If the results of the present study become a foundation for scanning parameters for Japanese patients, we believe that they will eventually lead to a reduction in medical radiation exposure for this patient population.

[Development of computer code PIETAII, for analysis of exposure dose from portable X-ray in neonatal intensive care unit].

The patients in NICU (Neonatal Intensive Care Unit) are more likely to get portable X-ray often while they are in the hospital. These patients potentially may get relatively more exposure dose in total in a short period of time. We developed a software to analyze the exposure dose for the patients in the incubator, which is called PIETAII (Patient Information of Exposure dose Total Analysis in NICU). Then, we compared the accuracy of PIETAII and SDEC (surface dose evaluation code) based on customary method. Using the 5 cm body thickness with exposure setting of 50 kV, 1 mAs, relative error between the customary method and the calculated dose by PIETAII and SDEC were 1.96% and 32.35%, respectively. PIETAII is a useful software to estimate the entrance surface dose using the exposure setting.

[Usefulness of criterion on which to operate coronary computed tomography angiography used dual source computed tomography comparisons with exposure dose of prospective electrocardiogram high-pitch spiral mode, low-pitch spiral mode, and step and shoot mode].

We believe that the patient exposure dose differs by heart rate for a coronary computed tomography angiography (CCTA), and we attempted to reduce patient exposure dose of the CCTA. Specifically, we made a clear difference of exposure dose between heart rate and optimal cardiac phase or some imaging methods. Next, we established criterion of the CCTA in our hospital, and usefulness was discussed. For examination methods, patients with a heart rate below 60 beats per minute (bpm) received a high-pitch spiral scan (Flash Spiral mode), those between 61 to 70 bpm received a step and shoot scan (SAS mode), and those of >70 bpm or an irregular heart rate received low-pitch spiral scan (Helical mode). The results of the clinical study showed that patient exposure dose reduced 87% in Flash Spiral mode (1.93±0.26 mSv) and 66% in SAS mode (4.88±1.24 mSv) compared with Helical mode (14.35±3.42 mSv). In our present study, we proved the usefulness of our criteria using CCTA. If the results of our present study become guidelines of CCTA users, we suggest that total patient exposure dose can be reduced.

[Evaluation of low dose chest expiratory high resolution computed tomography for diagnosis of air trapping].

In our hospital, expiratory high resolution computed tomography (HRCT) is being performed in patients with chronic obstructive pulmonary disease (COPD). Because expiratory HRCT is used in combination with inspiratory HRCT, it can provide less exposure according to diagnostic purposes. In the present study, we tried low-dose expiratory HRCT in terms of visual assessment and analysis software of phantom experiments. As a result, visual assessment in the dose reduction rate was about 50% to 75% against conventional exposure doses. Thoracic examinations are common in organs with high tissue weighting factors, and the present study shows a very effective means for medical exposure reduction.

[Development of a new method to estimate patient surface dose distributions in IVR].

Recently, the angiography system used for interventional radiology (IVR) provides a device for measuring dose-area product (DAP), which is compulsory in European countries. The usefulness of DAP is that one can observe patient dose in real time during IVR and can obtain an integral dose by overall IVR procedure without a dosimeter directly placed on a patient. It is important to know the most irradiated region (hot spot) of the patient's skin and its maximum value in the dose management of IVR, but this information cannot be obtained only in DAP. In this paper, we describe a new method to estimate patient surface dose distributions in IVR. We devised a sheet dubbed the "Number map", which does not obstruct the IVR procedure, to confirm the hot spot, and we developed software (named PIETA "Patient Information on Exposure Total Dose Analysis in IVR") to analyze the data from the Number map. Using this system, dose distributions of patient's skin were easily obtained, and we could easily perform patient dose management in IVR.

[Measurement of patient skin absorbed dose in ablation of paroxysmal atrial fibrillation and examination of treatment protocol].

The ablation for atrial fibrillation minute movement done in our hospital is 250 minutes or less, within an average time of 150 minutes during a fluoroscopic time of about 7 hours, with very large average inspection times numerical values. However, the skin-absorbed dose could be understood only from the numerical value of the area dosimeter. It was considered that the total dose that reached the threshold was sufficient, although radiation injury would not be reported from the ablation currently done at our hospital. Therefore, we aimed to examine the inspection protocol in this hospital, and to request the patient be given an inspection dose that was the average skin-absorbed dose by using the acryl board. The amount of a total dose for an inspection of 150 minutes of fluoroscopic time was about 2.7 Gy. Moreover, a value of 1.5 Gy was indicated in the hot spot as a result of repetition in some exposure fields. However, it was thought that the possibility of exceeding the threshold of 2 Gy depending on the inspection situation in the future and other factors was tolerable because these measurements were done so as not to overvalue it more than the necessary.