PATIENT-SPECIFIC ORGAN DOSE EVALUATION BASED ON MONTE CARLO SIMULATION AND DOSE METRICS IN PAEDIATRIC CHEST-ABDOMEN-PELVIS CT EXAMINATIONS.

This study aimed to determine organ doses based on Monte Carlo (MC) simulations for individual paediatric patients undergoing chest-abdomen-pelvis computed tomography (CT) examinations and to evaluate correlations of organ doses with dose metrics. MC simulations were performed by inputting detailed descriptions of a CT scanner, scanning parameters and CT images of 51 paediatric patients aged from 0 to 10 years into the simulation software. Organ doses for six radiosensitive organs were determined from dose distribution images obtained as the simulation results. The correlations of organ doses with dose metrics such as volume CT dose index, size-specific dose estimates (SSDEs), and organ-specific SSDEs were evaluated from the corresponding coefficients of determination. Organ doses for ages of 0-1 and 1-5 years were 22%-32% lower than those for ages of 5-10 years. Organ doses exhibited higher linear correlations with SSDEs and organ-specific SSDEs, and can be easily estimated using the linear regression.

Radiation Dose Reduction for Computed Tomography Localizer Radiography Using an Ag Additional Filter.

OBJECTIVE: This study aimed to assess the potential of an Ag additional filter attached to the bow tie filter of a computed tomography (CT) scanner to reduce the radiation dose in CT localizer radiography. METHODS: Radiation doses in CT localizer radiography with Cu and Ag additional filters were evaluated based on dose measurements and Monte Carlo simulations. Image quality evaluations of an adult torso phantom were performed, and the automatic exposure control performance was evaluated in terms of the water-equivalent thickness estimated from CT localizer radiographs. RESULTS: With the Ag additional filter, effective doses were approximately 72% to 75% lower than those with the Cu additional filter. The image quality and water-equivalent thickness with the Ag additional filter were similar to those with the Cu additional filter. CONCLUSIONS: The Ag additional filter helped significantly reduce radiation doses in CT localizer radiography while maintaining image quality and performance.

Correlation analysis of organ doses determined by Monte Carlo simulation with dose metrics for patients undergoing chest-abdomen-pelvis CT examinations.

OBJECTIVES: This study aimed to determine organ doses based on Monte Carlo (MC) simulations for individual patients undergoing routine adult chest abdomen-pelvis computed tomography (CT) examinations and to evaluate the correlations of organ doses with patient size and dose metrics. METHODS: MC simulations were performed by reading detailed descriptions of the CT scanner, scanning parameters, and CT images of phantoms and patients into the simulation software. The simulation models were validated by comparing the simulated doses with the doses measured by in-phantom dosimetry using radiophotoluminescent glass dosimeters and an adult anthropomorphic phantom, and organ doses for 80 patients were determined from the simulation results. To obtain patient size and dose metrics, body mass index and volume computed tomography dose index (CTDIvol) data were collected. Water equivalent diameter (WED) was calculated from the CT images of each patient. Size-specific dose estimates (SSDE) were calculated using CTDIvol and average WED over the scan range, and organ specific SSDE were calculated using the average CTDIvol and WED over each organ position. The correlations of organ doses with dose metrics were evaluated using coefficients of determination. RESULTS: Organ doses increased with patient size, and the doses for obese were approximately two to three times higher than those for underweight patients. Organ doses exhibited stronger linear relationships with organ specific SSDE (R2 ≥ 0.82) than other dose metrics. CONCLUSIONS: The linear regression fits between organ doses determined by MC simulation and organ-specific SSDE are valuable for simplified and accurate organ dose estimation for individual patients undergoing CT examinations.

Influence of seasonal variations on physical activity in older people living in mountainous agricultural areas.

Objectives: Increasing activity levels in older people is important for maintaining quality of life and ameliorating the risks of morbidity related to falls, depression, and dementia. This study aimed to clarify the seasonal variation effects on total energy expenditure, number of steps, time spent in low- and moderate- or high-intensity physical activities, and daily activities performed. Patients and Methods: This was a cross-sectional study of 22 community-dwelling older individuals (3 men, 19 women; mean age, 75.1 ± 7.3 years) living in three districts of Gero, Gifu, who participated in the Gero Salon Project hosted by the Social Welfare Councils. Evaluations were conducted in each season from September 2016 to August 2017. We used a uniaxial accelerometer, the Lifecorder device, which measures physical activity, and the Physical Activity Scale for the Elderly to evaluate activities of daily living. Data were analyzed using the multiple comparisons (Bonferroni correction) method. Results: Total energy expenditure and time spent in moderate- or high-intensity activities did not show seasonal variations. However, the lowest number of steps was taken during the winter, and the number of steps increased significantly from winter to spring. The time spent in low-intensity physical activities was significantly longer in the spring and summer than in the winter. There was no significant seasonal difference in total Physical Activity Scale for the Elderly score, leisure activities, domestic activities, or work-related activities. However, there was a significant difference between the summer and winter scores in "outdoor gardening," with the lowest score observed during the winter. Conclusions: With climate changes in the winter months, "outdoor gardening" becomes difficult, thus decreasing the number of steps taken. Therefore, it is necessary to identify other ways for older people to maintain physical activity during the winter season.