When performing lung cancer treatments using volumetric modulated arc therapy (VMAT) technique, dose error related to respiratory motion of tumors and multi leaf collimator (MLC) movement may occur. The dose error causes daily dose variation in multiple fractionations irradiation. The purpose of this study is to verify the influence of the respiratory motion and the MLC movement on the daily dose variation, and to confirm the feasibility of deciding robust planning parameter against the dose variation. We prepared 5 VMAT plans for imitating lung tumor in thorax dynamic phantom. Dose calculations of these plans were done taking into account the respiratory motions. We examined the relation between dose variation and two parameters that were number of respiration in an arc and MLC gap width. We presented the relationship between the dose variation and each parameters using regression analysis, and we could derive the approximation formula for estimating the dose variation using these parameters. We could estimate dose variation in another VMAT plans using the approximation formula and another plans parameters. By confirming dose variation in planning procedure using this estimation method, we may decide planning parameter taking the dose variation into account. So, we could establish the estimation method to decide adequate planning parameters in VMAT.
Purpose: The aim of this study was to reduce the exposed dose of radiotherapy treatment planning computed tomography (CT) by using low tube voltage technique. Materials and Methods: We used tube voltages of 80 kV, 100 kV, and 120 kV, respectively. First, we evaluated exposure dose with CT dose index (CTDI) for each voltage. Second, we compared image quality indexes such as modulation transfer function (MTF), noise power spectrum (NPS), and contrast to noise ratio (CNR) of phantom images with each voltage. Third, CT to electron density tables were measured in three voltages and monitor unit value was calculated along with clinical cases. Finally, CT surface exposed dose of chest skin was measured by thermoluminescent dosimeter (TLD). Results: In image evaluation MTF and NPS were approximately equal; CNR slightly decreased, 2.0% for 100 kV. We performed check radiation dose accuracy for each tube voltage with each model phantom. As a result, the difference of MU value was not accepted. Finally, compared with 120 kV, CTDIvol and TLD value showed markedly decreased radiation dose, 60% for 80 kV and 30% for 100 kV. Conclusion: Using a technique with low tube voltages, especially 100 kV, is useful in radiotherapy treatment planning to obtain 20% dose reduction without compromising 120 kV image quality.
Purpose: The purpose of this study was to validate the reduction of dark band (DB) artifact using iterative reconstruction (IR) of abdomen CT. Methods: Phantoms were arranged with and without small phantom assuming arm position at the body side (Phantom-A, -B). Image reconstruction methods were derived by the following four methods: filtered back projection (FBP), IR [adaptive iterative dose reduction using three-dimensional processing: AIDR-3D (MILD)], organ specific reconstruction (OSR), and Boost-3D (Boost). We evaluated DB artifact with CT values, standard deviation (SD) values, and profile curves using the four reconstruction methods. Results: CT values of artifact decreased with low tube current in Phantom-A. CT values of artifact were significantly increased (15–23 HU) in OSR and Boost compared to FBP and MILD (Phantom-A). SD values of artifact improved by IR method. However, IR method was not improved to CT values decreased by artifact (Phantom-A). CT values were not changed by the difference in image reconstruction methods in Phantom-B. Conclusion: IR method has an effect to reduce statistical noise, but reduced the CT value for DB artifact. On the other hand, the OSR and Boost methods are effective for the improvement of CT value in the DB artifact.
Purpose: Aim of this study was to investigate optimal threshold of Z score when evaluating statistics image of Alzheimer's disease visually. Method: We classified 53 clinical patients in control and target group, and evaluated the distribution of Z score calculated with statistical brain image analysis for magnetic resonance and perfusion single photon emission computed tomography (SPECT). The optimal Z score threshold was determined from statistical significance that compared previously mentioned groups. Results: Target group was able to classify significantly Z score at 1.25 from control group in wide region of parietal lobe with statistical brain image analysis for perfusion SPECT. Discussion: The optimal threshold is equal or less than 2.0, in the case of Z score variance is close to the standard normal distribution. In contrast, the threshold is over 2.0 in the case of Z score variance is more than 1.0, and then by using ordinary threshold 2.0, it cannot point out abnormality.
The purpose of our study was to investigate radiation dose for lower tube voltage CT using automatic exposure control (AEC). An acrylic body phantom was used, and volume CT dose indices (CTDIvol) for tube voltages of 80, 100, 120, and 135 kV were investigated with combination of AEC. Average absorbed dose in the abdomen for 100 and 120 kV were also measured using thermoluminescence dosimeters. In addition, we examined noise characteristics under the same absorbed doses. As a result, the exposure dose was not decreased even when the tube voltage was lowered, and the organ absorbed dose value became approximately 30% high. And the noise was increased under the radiographic condition to be an equal absorbed dose. Therefore, radiation dose increases when AEC is used for lower tube voltage CT under the same standard deviation (SD) setting with 120 kV, and the optimization of SD setting is crucial.
The purpose of this study is to decide the optimum exposure condition of Guthmann-method by the fuzzy measure theory. The samples for the fuzzy measure theory were created using the pelvis-phantom irradiated with various tube voltages (90–120 kV) and additional filters (0.5 mmAl+0.05 mmCu, 0.5 mmAl+0.1 mmCu). And we selected 6 samples on each exposure condition. The measuring points of Guthmann-method were specified as primary objective points. Sharpness, graininess and contrast were evaluated in each point. The fuzzy numerical integration was calculated with the rating score of each quality factor and the fuzzy measure. We set threshold to the fuzzy numerical integration and extracted the threshold sample which was able to visually recognize the measuring points on each exposure condition. We selected a sample which had the lowest entrance surface dose in the extracted images. And the exposure condition of this sample (110 kV, 5 mAs, 0.5 mmAl+0.05 mmCu) was adopted. The visual evaluation using the fuzzy measure theory may be useful as an examination method of the exposure condition for Guthmann-method.
This is the eighth investigation which has been carried out every 5 years since 1974 for the purpose of grasping the trend of X-ray devices and the radiographic condition. We gathered it up mainly on a radiographic condition, in this report. As for the chest radiography and double contrast gastrography, introduction of the flat panel detector (FPD) advanced in comparison with the last survey. Ratio of the imaging system at chest radiography was 65% for computed radiography (CR), 33% for FPD, 1% for screen/film (S/F), and 1% for others. The radiographic condition of FPD was current time product less than CR. Ratio of the imaging system at gastrography was 3% for CR, 48% for FPD, 34% for image intensifier-digital radiography (I.I.-DR), and 15% for S/F. The tube voltage and the exposure time were similar to the last survey time, but the tube current became lower. Through this survey, the change of the radiographic condition was seen in the radiography part where introduction of the FPD advanced. We think the continuous survey is necessary in future.
Diagnostic imaging has been shifted rapidly from film to monitor diagnostic. Consequently, Japan medical imaging and radiological systems industries association (JIRA) have recommended methods of quality control (QC) for medical imaging display systems. However, in spite of its need by majority of people, executing rate is low. The purpose of this study was to validate the problem including check items about QC for medical imaging display systems. We performed acceptance test of medical imaging display monitors based on Japanese engineering standards of radiological apparatus (JESRA) X-0093*A-2005 to 2009, and performed constancy test based on JESRA X-0093*A-2010 from 2010 to 2012. Furthermore, we investigated the cause of trouble and repaired number. Medical imaging display monitors had 23 inappropriate monitors about visual estimation, and all these monitors were not criteria of JESRA about luminance uniformity. Max luminance was significantly lower year-by-year about measurement estimation, and the 29 monitors did not meet the criteria of JESRA about luminance deviation. Repaired number of medical imaging display monitors had 25, and the cause was failure liquid crystal panel. We suggested the problems about medical imaging display systems.