Comparison of pediatric lens scattered dose measurements between axial 40-mm and helical 160-mm detector width computed tomography scan modes.

BACKGROUND: Reports comparing field lens doses between helical scans with a 40-mm detector width and axial scans with a 160-mm detector width using different computed tomography (CT) scanners are currently scarce. OBJECTIVE: To compare scatter doses for lenses between a helical scan with a 40-mm detector width and an axial scan with a 160-mm detector width when using different CT scanners in the context of pediatric chest examinations. MATERIALS AND METHODS: Two different CT machines were used: Revolution CT (GE Healthcare, Waukesha, WI) with a 256-row, 0.625-mm multidetector; and Aquilion ONE GENESIS Edition (Canon Medical Systems, Otawara, Japan) with a 320-row, 0.5-mm multidetector. Three pediatric anthropomorphic phantoms were used, with optically stimulated luminescence dosimeters (OSLDs) placed on the left and right lenses. The scatter dose values measured by the OSLDs were compared between a helical scan with a 40-mm detector width and an axial scan with a 160-mm detector width during pediatric chest CT examinations. RESULTS: Median equivalent doses for the helical and axial scans were 0.12 and 0.12 mSv/mGy for the newborn, 0.17 and 0.16 mSv/mGy for the 1-year-old, and 0.18 and 0.15 mSv/mGy for the 5-year-old, respectively, when using the Revolution CT. With the Revolution CT, no significant differences were observed in the scatter doses between helical and axial scans in the newborn and 1-year-old phantoms. However, the lens scatter dose for the helical scan was approximately 20-35% higher than that for the axial scan in the 5-year-old phantom (P<0.01). The median equivalent doses of eye lenses for the helical and axial scans were 0.12 and 0.07 mSv/mGy for the newborn, 0.07 and 0.05 mSv/mGy for the 1-year-old, and 0.14 and 0.12 mSv/mGy for the 5-year-old, respectively, when using the Aquilion ONE. With the Aquilion ONE, lens scatter doses for the helical scan were approximately 70%, 40%, and 30% higher in the newborn, 1-year-old, and 5-year-old phantoms, respectively, than those for the axial scan (P<0.01). CONCLUSIONS: When using the Aquilion ONE, lens scatter doses for the helical scan were significantly higher in all three phantoms than those for the axial scan. In contrast, when using the Revolution CT, the lens scatter dose for the helical scan was significantly higher in the 5-year-old phantom than that for the axial scan. These results suggest that although scattered doses may vary with respect to the CT scanner and body size, they are generally lower in the case of axial scans.

Impact of beam collimation of z-overscanning on dose to the lens and thyroid gland in paediatric thoracic computed tomography imaging.

BACKGROUND: Adaptive collimation reduces the dose deposited outside the imaged volume along the z-axis. An increase in the dose deposited outside the imaged volume (to the lens and thyroid) in the z-axis direction is a concern in paediatric computed tomography (CT). OBJECTIVE: To compare the dose deposited outside the imaged volume (to the lens and thyroid) between 40-mm and 80-mm collimation during thoracic paediatric helical CT. MATERIALS AND METHODS: We used anthropomorphic phantoms of newborns and 5-year-olds with 40-mm and 80-mm collimation during helical CT. We compared the measured dose deposited outside the imaged volume using optically stimulated luminescence dosimeters (OSLD) at the surfaces of the lens and thyroid and the image noise between the 40-mm and 80-mm collimations. RESULTS: There were significant differences in the dose deposited outside the imaged volume (to the lens and thyroid) between the 40-mm and 80-mm collimations for both phantoms (P < 0.01). CONCLUSION: Compared with that observed for 80-mm collimation in helical CT scans of the paediatric thorax, the dose deposited outside the imaged volume (to the lens and thyroid) was significantly lower in newborns and 5-year-olds with 40-mm collimation.

Effectiveness of low tube voltage scan in the exposure dose for lenses during paediatric thoracic CT examination: anthropomorphic phantoms study.

To determine whether using lower-tube voltage reduces the scattered dose for the lens during paediatric thoracic computed tomography (CT). Two paediatric anthropomorphic phantoms (ATOM Phantom, CIRS, Norfolk, Virginia, USA) representing a newborn and 5-year-old were placed on the gantry of CT scanner, and optically stimulated luminescence dosemeters were placed on the left and right lenses, in front of the left and right thyroid glands, in front of the left and right mammary glands, and in front of and behind the mammary gland level and we measured scattered dose of the optically stimulated luminescence dosemeter was compared for each phantom between 80 and 120 kVp. Significant differences were observed in the scatter doses for the lens between 80 and 120 kVp (p < 0.01). Compared with the 120 kVp scan, the scatter doses for the lens were ~15-40% lower in newborn and 5-year-olds using the 80 kVp scan during paediatric CT.

Quantitative Analysis of the Clinical Reasons Influencing the Frequency of Pediatric Head CT Examinations: A Single-Center Observation Study.

Epidemiological studies on radiation exposure from pediatric CT scans have attracted attention in terms of radiological protection. These studies have not taken into account the reasons why CT examinations were performed. It is presumed that there are clinical reasons that justify more frequent CT examinations in children. The purpose of this study was to characterize the clinical reasons why relatively high numbers of head CT examinations (NHCT) are frequently performed and to conduct a statistical analysis to determine the factors governing the NHCT. Patient information, the date of examination, and medical conditions for examination data stored on the radiology information system were used to investigate the reasons for undergoing CT examinations. The target facility was National Children's Hospital; data were obtained from March 2002 to April 2017, and the age of the study population was less than 16 years old. Quantitative analysis of the factors associated with frequent examinations was conducted by Poisson regression analysis. Among all patients who had a CT scan, 76.6% had head CT examinations, and 43.4% of children were under 1 year old at the time of the initial examination. There were marked differences in the number of examinations depending on the disease. The average NHCT was higher for children younger than 5 days of age. Among children less than 1 year of age with surgery, there was a marked difference between hydrocephalus, with a mean = 15.5 (95% CI 14.3,16.8), and trauma, with a mean = 8.3 (95% CI 7.2,9.4). In conclusion, this study revealed that NHCT was significantly higher in children who had undergone surgery than in those who had not been to the hospital. The clinical reasons behind patients with higher NHCT should be considered in investigating a causal relationship between CT exposure and brain tumors.

Computed tomography of the head and the risk of brain tumours during childhood and adolescence: results from a case-control study in Japan.

To clarify whether medical radiation exposure, especially from head computed tomography (CT), increases the risk of brain tumours in young patients in Japan, which ranks the second highest in the world in the number of paediatric CT examinations following the US. From 2011 to 2015, we performed a case-control study of 120 brain tumour patients and 360 appendicitis patients as controls. Reasons, the number of brain and head CT scans date were available from interviews. A cumulative radiation dose to the brain was calculated as a sum of doses received from head CT scans and from conventional X-rays and estimated using a reference table derived from a literature review of published studies. We performed conditional logistic regression to assess the risk of brain tumours from brain and head CT, and from conventional head X-ray procedures. The case group received on average 1.8 CTs to the brain area and 2.2 CTs to the whole head, with a mean estimated brain dose of 32 ±13 mGy. The odds ratio for developing a brain tumour from having a brain CT was 0.93 (95% confidence interval: 0.38-1.82). This was hardly altered when adjusting for parental educational history and for other diseases (history of neurological disease and attention-deficit disorder/attention-deficit hyperactivity disorder). Neither whole head CT nor cumulative brain dose to the brain increased the risk of glioma or of all brain tumours. Although this study conducted in Japan, where ranks second in the number of CT scans conducted in the world, did not show an increased risk of brain tumours related to CT scans, it should be taken with caution due to a case-control study with limited sample size.

Clinical indications for the use of computed tomography in children who underwent frequent computed tomography: a near-13-year follow-up retrospective study at a single institution in Japan.

Recent studies suggest a causal link of childhood leukemia and brain tumor with repeated computed tomography (CT) scans. The reasons why frequent CT scans are taken in a specific child remain unclear. The present study aimed to clarify the medical reasons why frequent CT examinations in children, and the characteristics of the diseases of those children that required multiple CT scans. A long-term follow-up retrospective study was conducted over a 12.75-year period at a single institution. Radiological reports were investigated that contained the indications for the CT scans. The clinical indications were classified for the examination of children under 16 years of age who underwent more than three CT scans into trauma, tumor, inflammation, and others. This study showed that 8.5% of CT examinations were done three times or more. The numbers of patients by indication were 23.3% for trauma, 5.3% for hydrocephalus, and 2.3% for appendicitis. The frequencies of trauma and inflammation decreased rapidly with an increasing number of CT scans. In particular, hydrocephalus brought high frequency more than ten scans. Regarding the frequencies of clinical indications by age groups, there was a significant difference (p<0.05). The near-13-year follow-up study indicated the main clinical indications for frequent CT scans in children were trauma and hydrocephalus. Multiple follow-up CT scans in children with hydrocephalus would be traded off against the resultant increase in brain tumor risk associated with CT exposure.

AUTOMATIC ACQUISITION OF CT RADIATION DOSE DATA: USING THE DIAGNOSTIC REFERENCE LEVEL FOR RADIATION DOSE OPTIMIZATION.

The present work describes that we try to construct a system that collects dose information that performed CT examination from multiple facilities and unified management. The results of analysis are compared with other National diagnostic reference level (DRL), and the results are fed back to each facility and the cause of the abnormal value is investigated for dose optimization. Medical information collected 139 144 tests from 33 CT devices in 13 facilities. Although the DRL of this study is lower than that of Japan DRL, it was higher than the DRL of each country. When collecting all the examination, it is thought that the variation of the dose due to the error other than the intended imaging site is large. In future, we should continue to collect information in order to DRL renewal and we also think that it is desirable to collect information on physique and detailed scan region as well.

Numerical Analysis of Organ Doses Delivered During Computed Tomography Examinations Using Japanese Adult Phantoms with the WAZA-ARI Dosimetry System.

A dosimetry system for computed tomography (CT) examinations, named WAZA-ARI, is being developed to accurately assess radiation doses to patients in Japan. For dose calculations in WAZA-ARI, organ doses were numerically analyzed using average adult Japanese male (JM) and female (JF) phantoms with the Particle and Heavy Ion Transport code System (PHITS). Experimental studies clarified the photon energy distribution of emitted photons and dose profiles on the table for some multi-detector row CT (MDCT) devices. Numerical analyses using a source model in PHITS could specifically take into account emissions of x rays from the tube to the table with attenuation of photons through a beam-shaping filter for each MDCT device based on the experiment results. The source model was validated by measuring the CT dose index (CTDI). Numerical analyses with PHITS revealed a concordance of organ doses with body sizes of the JM and JF phantoms. The organ doses in the JM phantoms were compared with data obtained using previously developed systems. In addition, the dose calculations in WAZA-ARI were verified with previously reported results by realistic NUBAS phantoms and radiation dose measurement using a physical Japanese model (THRA1 phantom). The results imply that numerical analyses using the Japanese phantoms and specified source models can give reasonable estimates of dose for MDCT devices for typical Japanese adults.

Calculating patient-specific organ doses from adult body CT scans by Monte Carlo analysis using male-individual voxel phantoms.

Computed tomography (CT) dose calculators such as the WAZA-ARI are useful for estimating the radiation dose from CT examination. This study determined correction coefficients for estimating organ doses to patients of any size attended to in daily clinical practice. To this end, the authors constructed voxel phantoms based on the CT images of patients of different size and simulated radiation transport in CT examinations to obtain organ doses using Monte Carlo simulation. The results show that the linear relationship between effective diameter and organ dose can predict patient-specific organ doses. The effective diameter-based prediction can provide accuracy within an error of ±10%, whereas an error of >20% was observed only in the liver and bladder. These results may contribute to practical irradiation dose calculation from a CT examination depending on individual patient size within a certain degree of accuracy.

WAZA-ARI: computational dosimetry system for X-ray CT examinations II: development of web-based system.

A web-based dose computation system, WAZA-ARI, is being developed for patients undergoing X-ray CT examinations. The system is implemented in Java on a Linux server running Apache Tomcat. Users choose scanning options and input parameters via a web browser over the Internet. Dose coefficients, which were calculated in a Japanese adult male phantom (JM phantom) are called upon user request and are summed over the scan range specified by the user to estimate a normalised dose. Tissue doses are finally computed based on the radiographic exposure (mA s) and the pitch factor. While dose coefficients are currently available only for limited CT scanner models, the system has achieved a high degree of flexibility and scalability without the use of commercial software.

WAZA-ARI: computational dosimetry system for X-ray CT examinations. I. Radiation transport calculation for organ and tissue doses evaluation using JM phantom.

A web system of WAZA-ARI is being developed to assess radiation dose to a patient in a computed tomography examination. WAZA-ARI uses one of organ dose data sets corresponding to the options selected by a user to describe examination conditions. The organ dose data have been derived by the Particle and Heavy Ion Transport code system, combined with Japanese male (JM) phantom. The configuration of JM phantom is adjusted to the averaged JM adult. In addition, a new phantom is introduced by removing arms from JM phantom to take into account for dose calculations in torso examinations. Some of the organ doses by JM phantom without arms are compared with results obtained by using a MIRD-type phantom, which was applied in some previous dosimetry systems.