Tou-Rong Chen

Population dose from medical exposure in Taiwan for 2008

PURPOSE The largest contribution to the population dose from man-made ionizing radiation sources is the medical exposure. Exposure to patients from medical examinations is of interest because it is a global indicator for the quality of radiology practice. Due to the different healthcare systems and the considerable variations in the equipment and manpower in radiology, the population dose from medical exposure varies by a large extent in different countries. This dose from different diagnostic procedures provides information that can be used to establish national reference levels. It is also useful to determine the priority in terms of dose reduction so as to optimize the protection of patients in a cost-effective manner. In the present work, the collective effective doses due to different medical modalities were estimated for the Taiwan population in 2008. METHODS The collective effective dose from medical exposure was calculated using information on the number of procedures and the average effective dose per procedure. The frequency of procedures was extracted from the National Health Insurance (NHI) research database. The enrollment of Taiwan population in the NHI program was 99.48% in 2008. The average effective dose per procedure was derived from hospital surveys, measured data, and published results. RESULTS Estimates of the collective effective dose were made for different medical modalities, i.e., the conventional radiography and fluoroscopy, computed tomography, interventional fluoroscopy, nuclear medicine, and dental radiography. Each modality was further divided into relevant classes by the body part or organ system. Among 23 037 031 Taiwan population in 2008, the annual examination frequencies per 1000 population were 550, 55.1, 15.6, 13.6, and 112 for the conventional radiography and fluoroscopy, computed tomography, interventional fluoroscopy, nuclear medicine, and dental radiography, respectively. The corresponding collective effective doses were 3277, 8608, 2743, 2303, and 28 man-Sv, respectively. Thus, the average effective dose per caput was 0.74 mSv, which was in the range of 0.3-1.5 mSv for the 12 European countries estimated for 2008. CONCLUSIONS In the period from 1997 to 2008, the procedure frequency per 1000 population increased by a factor of 2.3 for computed tomography, 2.2 for interventional fluoroscopy, 1.8 for conventional radiography and fluoroscopy, and 1.5 for nuclear medicine. It demonstrated that the medical utilization of imaging facilities raised rapidly.

Gait Speed Measure: The Effect of Different Measuring Distances and the Inclusion and Exclusion of Acceleration and Deceleration

The purposes of this study were to examine the effects of different distances and the inclusion and exclusion of acceleration and deceleration distances on the measurement of self-paced and fastest gait speeds in younger and older adults. The self-paced and fastest gait speeds of younger and older adults were measured over 4-m and 10-m walkways with the acceleration and deceleration distances included and excluded in the measuring distance. The results indicated gait speeds (both self-paced and fastest) measured over different distances were comparable only if a distance for acceleration and deceleration was excluded from the measuring distance to obtain stable and comparable gait speeds. Similar results were found for younger and older groups.

Dose reconstruction for residents living in 60Co-contaminated rebar buildings

The first 60Co-contaminated rebar building was discovered in Taipei city in 1992. As of 18 July 1997, 144 buildings with 1,327 housing units were confirmed to contain 60Co-contaminated rebars. All these reinforced concrete buildings were constructed between 1982 and 1984. Thousands of residents have been exposed to ionizing radiation of various degrees. Preliminary assessments by the Atomic Energy Council showed that the accumulated maximal doses ranged from a few mSv to several Sv. The purpose of this work was to reconstruct more reliable individual doses for epidemiologic and medical uses. This reconstruction provided the best estimated doses as well as conceivable upper and lower bounds. The variation of residential day-life activities by individual members in a family was considered according to their sex, age, profession, etc. Intensive data on exposure rates were collected using thermoluminescent dosimeters positioned at 1 m height and 1 m x 1 m intersections with additional measurements at special locations such as bed, sofa, dining table, etc. Thermoluminescent dosimeter measurements were performed in all 24 residences studied in this work. This showed that the Atomic Energy Council maximal doses were 2-6 times higher than the present best estimated doses. Among all family members, elders and housewives received the highest doses; children received the lowest doses. The difference in doses among all family members belonging to different cohort categories is within a factor of two.

Radon and Radon Progeny in the Carlsbad Caverns

ABSTRACT Measurements were made in July 1994 to determine air exchange rate, aerosol characteristics, radon concentrations, and radon progeny activity size distributions in the Carlsbad Caverns. The measured radon concentrations were stable at a level of 1821 ± 55 Bq m−3 (mean ±SD). Using a SF6 trace gas method, it was determined that stagnant air in the Caverns was exchanged once every 18 days. The stagnant air was a key factor in maintaining stable environmental conditions and radon concentration. The low air exchange and few aerosol sources inside the Caverns also contributed to the low aerosol concentrations of between 200 and 400 cm −3—orders of magnitude lower than mining, indoor, and outdoor environments. The alpha spectrum showed radon progeny but no thoron progeny, which may be a result of the long transport time for radioactive gases to diffuse from the deep rock to the cave. The activity size distribution of radon progeny showed typical bimodal distributions with higher unattached fractions [69...

Ambient and personal dose assessment of a container inspection site using a mobile X-ray system.

Ambient monitor and phantom studies of absorbed and effective doses by TLDs were carried out in a non-intrusive inspection station for containers, Terminal I, of Taichung harbor, Taiwan. The doses from the X-ray scan in the control room and driver waiting room, located outside of the radiation control area, were quite small and could not be distinguished from the natural background radiation. The doses in the driver cab and the inspector cab of the X-ray scan car were also within background radiation levels. The protection wall, a 40-cm thick concrete barrier, can effectively attenuate the intensity of the primary X-ray scan. The possible effective dose of a person in the container or trailer is about 3.15 ± 0.23 μSv/scan and 2.31 ± 0.38 μSv/scan. This dose is below the annual background dose. If someone was to be scanned by the X-ray, the effective dose would be at an acceptable level.

POPULATION DOSE FROM MEDICAL DIAGNOSTIC EXPOSURE IN TAIWAN

Medical exposure showed a continuous increasing trend. This trend was due to the growth of diagnostic procedures such as computed tomography (CT) and interventional fluoroscopy (IVF). In the present work, results of a recent study on medical exposure in Taiwan are reported. This study analysed data from the National Health Insurance Research Database. Surveyed data on the dose indices, including the entrance surface dose in radiography, dose area product in fluoroscopy, CT dose index in CT and mean glandular dose in mammography, were applied. Using programmes and databases, dose indices were converted to the effective dose. For the year 2008, individual effective doses in Taiwan were estimated as 0.16, 0.37, 0.12 and 0.12 mSv for conventional radiography and fluoroscopy, CT, IVF and nuclear medicine, respectively. The total collective effective dose and the effective dose per individual for medical exposure were 17 788 person-Sv and 0.77 mSv, respectively.

A Reliability Study for Standing Functional Reach Test Using Modified and Traditional Rulers

The purposes of the study were (1) to estimate the standing reach distance, test-retest, and interrater reliability of the functional reach test using traditional and modified rulers and (2) to evaluate the difference in the scores based on one trial, the mean of two or of three trials. Sixty-four individuals (M age = 36.3 yr., SD = 19.5, range = 19 to 70 years; 24 men, 40 women) volunteered to participate. Differences in measurements were examined. The intraclass correlation coefficient (ICC) was used to assess the test-retest and interrater reliability. Analysis indicated that the reach score measured by the rulers were not statistically significantly different, but the three measurements were significantly different. Reliability estimates were similar for the two mean scores, the mean of two trials (ICC2,2 = 0.87–1.00) or three trials (ICC2,3 = 0.89–1.00). The standard error of measurement (SEM) was always smaller when the modified ruler was used than when the traditional ruler was used. Performance with the modified ruler is an alternative to that with a traditional ruler. The mean of two trials as a measure of performance of reach distance when standing is recommended with either ruler.

The Population Effective Dose of Medical Computed Tomography Examinations in Taiwan for 2013

Purpose To evaluate the annual effective dose per capita attributed to computed tomography (CT) examinations in 2013 and to predict the population effective dose from 2000 to 2013 in Taiwan. Methods A CT examination database collected from 30 hospitals was divided into 22 procedures and classified into six regions: head, neck, chest, abdomen, pelvis, and other, respectively. The effective doses in different regions were evaluated by dose-length product (DLP) multiplied by conversion factors. Results The CT scan dose parameters were collected from 4,407 patients. For the six scanned regions, the percentages of patients scanned were: head (39.8%), neck (3.9%), chest (23.3%), abdomen (26.7%), pelvis (4.8%), and other (1.6%), respectively. The DLPs per patient (mGy·cm/patient) were head (1,071±225), neck (1,103±615), chest (724±509), abdomen (1,315±550), pelvis (1,231±620) and other (1,407±937), respectively. The number of CT examinations increased rapidly, with an average annual growth rate of 7.6%. The number of CT examinations in 2013 was 2.6 times that in 2000. The population effective dose was 0.30 mSv per capita in 2000 and increased to 0.74 mSv per capita in 2013, with an annual growth rate of 7.2%. The growth trend indicates that the effective dose will continue to rise in Taiwan. Conclusion Some strategies should be applied to cope with this growth. Defining the CT dose reference level stipulated in official recommendations and encouraging the use of iterative reconstruction imaging instead of filtered back-projection imaging could be a useful method for optimizing the effective dose and image quality.

Nanometer Particle Size and Concentration from Thoron Radiolysis

ABSTRACT The activity and number size distributions of 212Pb- and 212Bi-borne nanometer particles have been measured by the diffusion battery. Bimodal peaks associated with molecular clusters and coagulation particles were found. The activity median thermodynamic diameter and the geometric standard deviation were determined. It showed that both the activity median thermodynamic diameter and the geometric standard deviation increased with decreasing total flow rate. This was attributed to the longer mean residence time of thoron progeny in the sampling chamber for smaller total flow rate. Consequently, thoron progeny ions had better chance to collide, combine, and grow to a larger size. It also indicated that at constant flow rates the number concentration measured by the ultrafine condensation particle counter was greater for lower humidity. A lower humidity suggested less electron scavengers or smaller neutralization rates and thus larger cluster sizes. A comparison between the activity and number size d...

Surveyed data for structural shielding calculations of radiographic x-ray installations in Taiwan.

AbstractThe use of surveyed data on the x-ray tube workloads and clinical exposure parameters was suggested in NCRP Report No. 147 for the structural shielding design of medical x-ray installations. To guide the shielding design of radiographic x-ray rooms in Taiwan, a large-scale survey was conducted to collect information required for the computations of the transmissions from broad x-ray beams through shielding materials. Surveyed data were collected during one week from 10,750 projections of 6,657 examinations in 13 radiographic rooms from nine hospitals. This survey was the first time that this type of clinical data has been collected in Taiwan on a large scale. The surveyed total workload was divided into separate contributions from x-ray projections directed at the floor, the wall bucky, and all barriers (used for secondary barriers). Based on the surveyed workload distributions, the unshielded air kerma per patient at 1 m from the source was calculated by the PCXMC program using surveyed x-ray tube parameters on the generator waveform, anode material, target angle, and filtration. Subsequently, the transmissions of x-rays through different barrier materials were computed by considering the average workloads and the average workloads plus one standard deviations. The latter computations were for a sensitivity study to find the influence of workload variations in different hospitals on the shielding requirements. All surveyed data and calculated results were compared with corresponding values given in NCRP 147 to analyze the radiographic imaging differences between Taiwan and U.S.