Yuta Matsunaga

Evaluation of organ doses and effective dose according to the ICRP Publication 110 reference male/female phantom and the modified ImPACT CT patient dosimetry.

We modified the Imaging Performance Assessment of CT scanners (ImPACT) to evaluate the organ doses and the effective dose based on the International Commission on Radiological Protection (ICRP) Publication 110 reference male/female phantom with the Aquilion ONE ViSION Edition scanner. To select the new CT scanner, the measurement results of the CTDI100,c and CTDI100,p for the 160 (head) and the 320 (body) mm polymethylmethacrylate phantoms, respectively, were entered on the Excel worksheet. To compute the organ doses and effective dose of the ICRP reference male/female phantom, the conversion factors obtained by comparison between the organ doses of different types of phantom were applied. The organ doses and the effective dose were almost identical for the ICRP reference male/female and modified ImPACT. The results of this study showed that, with the dose assessment of the ImPACT, the difference in sex influences only testes and ovaries. Because the MIRD‐5 phantom represents a partially hermaphrodite adult, the phantom has the dimensions of the male reference man including testes, ovaries, and uterus but no female breasts, whereas the ICRP male/female phantom includes whole‐body male and female anatomies based on high‐resolution anatomical datasets. The conversion factors can be used to estimate the doses of a male and a female accurately, and efficient dose assessment can be performed with the modified ImPACT. PACS number: 87.53.LY, 87.57.Q‐, 87.57.‐s

Effective radiation doses of CT examinations in Japan: a nationwide questionnaire-based study

OBJECTIVE The aims of this study were to estimate the effective radiation doses from CT examinations of both adults and children in Japan and to study the impact of various scan parameters on the effective doses. METHODS A questionnaire, which contained detailed questions on the CT scan parameters employed, was distributed to 3000 facilities throughout Japan. For each scanner protocol, the effective doses for head (non-helical and helical), chest and upper abdomen acquisitions were estimated using ImPACT CT Patient Dosimetry Calculator software v. 1.0.4 (St Georges Hospital, London, UK). RESULTS The mean effective doses for chest and abdominal examinations using 80-110 kV were significantly lower than those using 120 kV. However, there was no statistically significant difference in the mean effective doses for head scans between facilities employing 80-110 kV and 120 kV. In chest and abdominal examinations, the mean effective doses using CT scanners from Western manufacturers [Siemens (Forchheim, Germany), Philips (Eindhoven, Netherlands) and GE Medical Systems (Milwaukee, WI)] were significantly lower than those of examinations using Japanese scanners [Hitachi (Kashiwa, Japan) and Toshiba (Otawara, Tochigi, Japan)], except for in paediatric chest examinations. CONCLUSION The mean effective doses for adult head, chest and abdominal CT examinations were 2.9, 7.7 and 10.0 mSv, respectively, whereas the corresponding mean effective doses for paediatric examinations were 2.6, 7.1 and 7.7 mSv, respectively. ADVANCES IN KNOWLEDGE Facilities using CT scanners by Western manufacturers commonly adopt low-tube-voltage techniques, and low-tube-voltage CT may be useful for reducing the radiation doses to the patients, particularly for the body region.

Effect of tube current modulation for dose estimation using a simulation tool on body CT examination

The purpose of this study was to evaluate the effect of tube current modulation for dose estimation of a body computed tomography (CT) examination using a simulation tool. The authors also compared longitudinal variations in tube current values between iterative reconstruction (IR) and filtered back-projection (FBP) reconstruction algorithms. One hundred patients underwent body CT examinations. The tube current values around 10 organ regions were recorded longitudinally from tube current information. The organ and effective doses were simulated by average tube current values and longitudinal modulated tube current values. The organ doses for the bladder and breast estimated by longitudinal modulated tube current values were 20 % higher and 25 % lower than those estimated using the average tube current values, respectively. The differences in effective doses were small (mean, 0.7 mSv). The longitudinal variations in tube current values were almost the same for the IR and FBP algorithms.

Dose evaluation for foetal computed tomography with a 320-row unit in wide-volume mode and an 80-row unit in helical scanning mode: a phantom study

The purpose of this study was to evaluate the maternal and foetal effective doses during foetal computed tomography (CT) and to compare the radiation dose, dose profile and image noise on 80-row CT in helical scanning mode and 320-row CT in wide-volume scanning mode. The radiation doses were measured using thermoluminescent dosemeters implanted at various organ sites of an anthropomorphic pregnant phantom. The foetal doses in the 320-row multi-detector CT (MDCT) and 80-row MDCT units were higher than the volume CT dose index (CTDIvol). The dose profile in the 320-row MDCT overlapped in two places but showed no overlap in the 80-row MDCT. There were no significant differences in image noise between the two scanning modes. The foetal dose evaluation by CTDIvol may underestimate the foetal radiation risk. When using the wide-volume mode, operators must take into account the number of scans and overlap between volumetric sections.

EVALUATION OF THE CT DOSE INDEX FOR SCANS WITH AN ECG USING A 320-ROW MULTIPLE-DETECTOR CT SCANNER

The relationship between heart rate (HR) and computed tomography dose index (CTDI) was evaluated using an electrocardiogram (ECG) gate scan for scan applications such as prospective triggering, Ca scoring, target computed tomography angiography (CTA), prospective CTA and retrospective gating, continuous CTA/CFA (cardiac functional analysis) and CTA/CFA modulation. Even in the case of a volume scan, doses for the multiple scan average dose were similar to those for CTDI. Moreover, it was found that the ECG gate scan yields significantly different doses. When selecting the optimum scan, the doses were dependent on many factors such as HR, scan rotation time, active time, prespecified cardiac phase and modulation rate. Therefore, it is necessary to take these results into consideration when selecting the scanning parameters.

SWALLOWING COMPUTED TOMOGRAPHY: DOSE ESTIMATION IN A PHANTOM STUDY CONDUCTED AT VARIOUS PATIENT RECLINING ANGLES

Swallowing computed tomography (SCT) is a relatively new technique for the morphological and kinematic analyses of swallowing. However, no optimal scan protocols are available till date. We conducted the present SCT study to estimate the patient dose at various patient reclining positions. A RANDO phantom with a thermoluminescent dosemeter was placed on a hard Table board in a semi-reclining position at the centre and off-centre. According to predetermined scan protocols, irradiation was performed to acquire scanograms at reclining angles of 55° and 65°. The effective dose was the lowest at the centre 45° (3.8 mSv) reclining angle. Comparison between the off-centre (4.6 mSv at 55°, 6.8 mSv at 65°) and centre (4.5 mSv, 5.8 mSv) values suggested that the off-centre position is undesirable with regard to the patient dose. Accordingly, we believe that SCT methods must be revised on the basis of these factors.

Diagnostic reference levels and achievable doses for common computed tomography examinations: Results from the Japanese nationwide dose survey

OBJECTIVE: To propose a new set of Japanese diagnostic reference levels (DRLs) and achievable doses (ADs) for 2017 and to verify the usefulness of Japanese DRLs (DRLs 2015) for CT, by investigating changes in the volume CT dose index (CTDIvol) from 2014 to 2017. METHODS: Detailed information on the CT scan parameters used throughout Japan were obtained by questionnaire survey. The CTDIvol and dose-length product for the 11 commonest adult and 6 commonest paediatric CT examinations were surveyed and compared with 2014 data and DRLs 2015. RESULTS: Evaluations of adult head (helical), and abdomen and pelvis without contrast agent, paediatric chest without contrast agent, and abdomen and pelvis without contrast agent showed a slightly lower mean CTDIvol in 2017 than in 2014 (t-test, p < 0.05). The interquartile range of CTDIvol for all 2017 examinations was lower than in 2014. CONCLUSIONS: This study verified the lower mean, 75th percentile, and interquartile range by investigating changes in the CTDIvol from 2014 to 2017. The DRLs 2015 contributed to CT radiation dose reduction. ADVANCES IN KNOWLEDGE: The widespread implementation of iterative reconstruction algorithms and low-tube voltage in CT scanners is likely to facilitate further reduction in the CT radiation dose used in Japan. Although radiological technologists may require further education on appropriate CTDIvol and DLP usage, the DRLs 2015 greatly contributed to the reduction of the CT radiation dose used in Japan.

PATIENT EXPOSURE DURING PLAIN RADIOGRAPHY AND MAMMOGRAPHY IN JAPAN IN 1974–2014

We investigated changes in the entrance skin dose (ESD) and the mean glandular dose (MGD) during plain radiography or mammography in Japan from 1974 to 2014. Surveys regarding the conditions used for plain radiography and mammography were performed throughout Japan in 1974, 1979, 1989, 1993, 1997, 2001, 2003, 2007, 2011 and 2014. The anatomical regions considered were categorised as follows: skull anteroposterior (AP), lumbar AP, lumbar lateral (LAT), pelvis (AP), ankle, chest posteroanterior (PA), Guthmann (lateral pelviography for pregnant women), infant hip joint and mammography. The doses for all anatomical regions decreased from 1974 to 1993. The MGD for mammography remained low from 1993 to 2014, and the ESDs for chest (PA) radiography trended upward. After the 2000s, the use of digital imaging increased in Japan. This is the first long-term study to examine changes in ESDs and MGDs in Japan.

Fetal dose conversion factor for fetal computed tomography examinations: A mathematical phantom study

Abstract This study aimed to examine the relationship between fetal dose and the dose–length product, and to evaluate the impact of the number of rotations on the fetal doses and maternal effective doses using a 320‐row multidetector computed tomography unit in a wide‐volume mode. The radiation doses for the pregnant woman and the fetus were estimated using ImPACT CT Patient Dosimetry Calculator software for scan lengths ranging from 176 to 352 mm, using a 320‐row unit in a wide‐volume mode and an 80‐row unit in a helical scanning mode. In the 320‐row unit, the fetal doses in all scan lengths ranged from 3.51 to 6.52 mGy; the maternal effective doses in all scan lengths ranged from 1.05 to 2.35 mSv. In the 80‐row unit, the fetal doses in all scan lengths ranged from 2.50 to 3.30 mGy; the maternal effective doses in all scan lengths ranged from 0.83 to 1.68 mSv. The estimated conversion factors from the dose–length product (mGy・cm) to fetal doses (mGy) for the 320‐row unit in wide‐volume mode and the 80‐row unit in helical scanning mode were 0.06 and 0.05 (cm−1) respectively. While using a 320‐row MDCT unit in a wide‐volume mode, operators must take into account the number of rotations, the beam width as automatically determined by the scanner, the placement of overlap between volumetric sections, and the ratio of overlapping volumetric sections.

Energy dependence and angular dependence of an optically stimulated luminescence dosimeter in the mammography energy range

&NA; This study aimed to investigate the energy dependence and the angular dependence of commercially available optically stimulated luminescence (OSL) point dosimeters in the mammography energy range. The energy dependence was evaluated to calculate calibration factors (CFs). The half‐value layer range was 0.31–0.60 mmAl (Mo/Mo 22–28 kV, Mo/Rh 28–32 kV, and W/Rh 30–34 kV at 2‐kV intervals). Mo/Rh 28 kV was the reference condition. Angular dependence was tested by rotating the X‐ray tube from −90° to 90° in 30° increments, and signal counts from angled nanoDots were normalized to the 0° signal counts. Angular dependence was compared with three tube voltage and target/filter combinations (Mo/Mo 26 kV, Mo/Rh 28 kV and W/Rh 32 kV). The CFs of energy dependence were 0.94–1.06. In Mo/Mo 26–28 kV and Mo/Rh 28–32 kV, the range of CF was 0.99–1.01, which was very similar. For angular dependence, the most deteriorated normalized values (Mo/Mo, 0.37; Mo/Rh, 0.43; and W/Rh, 0.58) were observed when the X‐ray tube was rotated at a 90° angle, compared to 0°. The most angular dependences of ± 30°, 60°, and 90° decreased by approximately 4%, 14%, and 63% respectively. The mean deteriorated measurement 30° intervals from 0° to ± 30° was 2%, from ± 30° to ± 60° was 8%, and from ± 60° to ± 90° was 40%. The range of energy dependence in typical mammography energy range was not as much as that in general radiography and computed tomography. For accurate measurement using nanoDot, the tilt needs to be under 30°.