[Evaluation of the Image Registration Program for Portal Images Using CR and DRR Images in Radiation Therapy].

In this study, computer simulations and experiments were used to verify the accuracy of a two-dimensional image registration program (program) for portal images that we previously developed. The program used a computed radiography cassette system and digitally reconstructed radiography images as planning images for external beam radiation therapy. Using this program, we also investigated the reason two-dimensional automatic image registration images experienced large misregistration in clinical practice using commercial image registration systems. Mutual information and normalized mutual information were used as the registration criteria. To investigate the influence of image background with or without a region of interest (ROI), results of image registrations were compared. Parameters of image registration were defined as translation in the horizontal and vertical directions (x and y, respectively) and rotation (θ) around the axis perpendicular to the x-y plane. There was no significant difference in image registration arising from the difference between mutual information and normalized mutual information. Image registration was improved with a ROI. Regardless of the registration criteria, errors in image registration with a ROI in the experimental study were ≤1.2 mm in directions x and y and ≤1.0 degree in rotation θ. We found that image registration required setting up as close to the planned position as possible.

[Failure analysis of medical linear accelerator with reliability analyses].

We analyzed a number of cases about the Linac troubles in our hospital and have examined the effect of preventive maintenance with Weibull analysis and exponential distribution from April 2001 to March 2012. The total failure by irradiation disabled was 1, 192. (1) Medical linear accelerator (MLC) system was 24.0%, (2) radiation dosimetry system 13.1%, and the (3) cooling-water system was 26.5%. It accounts for 63.6% of the total number of failures. Each parameter value m, which means the shape parameter, and the failure period expectancy of parts µ were (1) 1.21, 1.46/3.9, 3.8 years. 3.7, 3.6 years. (2) 2.84, 1.59/6.6, 4.3 years. 6.7, 5.9 years. (3) 5.12, 4.16/6.1, 8.5 years. 6.1, 8.5 years. Each shape parameter was m>1. It is believed that they are in the worn-out failure period. To prevent failure, MLC performance should be overhauled once every 3 years and a cooling unit should be overhauled once every 7 years. Preventive maintenance is useful in assessing the failure of radiation therapy equipment. In a radiation dosimetry part, you can make a preemptive move before the failure by changing the monitor's dosimeter board with a new part from the repairs stockpiled every 6 months for maintenance.

[Effect of changing into slippers on the pollution situation in the nuclear medicine management district].

Changing into slippers when entering the nuclear medicine management district prevented pollution expansion. Accidents involving patients falling occurred in university facilities. It was thought that changing slippers was the cause. The pollution situation was measured in three facilities by using the smear method and the direct technique to examine the effect of changing slippers. The current state was measured. After pollution prevention guidance was continuously done, pollution expansion was measured; three weeks of measurements were compared. Pollution was detected in the first period of weeks at a frequency of 19 times. For the latter period, it was detected 6 times. Half the pollution was in the restroom. Pollution was reduced by doing pollution prevention guidance for the restroom. Patients' falls occur even if they change slippers. Falling accidents can be decreased.

[Improvement of method of determining fluoroscopy loading factor in digital angiographic x-ray system with a flat panel detector].

A catheterization study and treatment of coronary arteriopathy are performed by investigating the coronary artery from different angles to find the region to be treated. In doing so, our system always started from the initial value of the loading factor, using this only for the first time, and the system started from the last loading factor the second time and later, at all angles. Therefore, depending on the angle, the loading factor at the start of fluoroscopy sometimes became unstable, and it took time to stabilize. This made the starting image too dark (undershoot x-ray condition) or fogged by halation (overshoot x-ray condition). With the system manufacturer, we developed a tube voltage and tube current setting method for the initial value of the loading factor. We installed software which preset the loading factor at the start of fluoroscopy depending on the angle, and an auto memory function of the last loading factor for each angle. This function allows the system to control the tube voltage and tube current for any angle. As a result, the system can acquire a more stabilized image from the start of fluoroscopy. This method of determining the initial loading factor is an effective way to stabilize the fluoroscopy image quickly.

[CT scanners with automatic focus alteration capability].

Heat accumulation in X-ray tubes results in disarrangement of focus owing to heat expansion of the anode. CT scanners with automatic focus alteration capability have been developed to counteract this problem. We compared CT scanners with and without focus alteration capabilities and discuss the effect of focus disarrangement on the CT images. Images were obtained when heat accumulation was high and low. Subtraction images were made to define the disarrangement of focus. A comparison was made between CT scanners with and without automatic focus alteration capability. ROI was selected and changes in CT values, SD, and slice thickness were observed under changing anode heat accumulation. Results indicated that images from both scanners showed disarrangement of the focus and elevation of CT values as anode heat accumulated. However, the scanner with automatic focus alteration produced images with less focus disarrangement from the center of the slice and less elevation of CT values. Scanners with automatic focus alteration are less prone to the focus disarrangement and elevation of CT values caused by anode heat accumulation and enable reproducible images to be obtained.