Radiological protection in human research ethics using a case study: toward update of the ICRP Publication 62.

The benefits of biomedical research involving humans are well recognised, along with the need for conformity to international standards of science and ethics. When human research involves radiation imaging procedures or radiotherapy, an extra level of expert review should be provided from the point of view of radiological protection. The relevant publication of the International Commission for Radiological Protection (ICRP) is now three decades old and is currently undergoing an update. This paper aims to provoke discussions on how the risks of radiation dose and the benefits of research should be assessed, using a case study of diagnostic radiology involving volunteers for whom there is no direct benefit. Further, the paper provides the current understanding of key concepts being considered for review and revision-such as the dose constraint and the novel research methods on the horizon, including radiation biology and epidemiology. The analysis revisits the perspectives described in the ICRP Publication 62, and considers the recent progress in both radiological protection ethics and medical research ethics.

External Doses Available for Epidemiological Studies Related to the Fukushima Health Management Survey: First 4-month Individual Doses and Municipality-average Doses for the First Year.

BACKGROUND: One of the components of the Fukushima Health Management Survey (FHMS) is the Basic Survey, which estimates individual external doses for the first 4 months after the 2011 nuclear power plant accident. However, external exposure continues long-term. According to estimations by international organizations, the external dose during the first year accounts for a significant part of the long-term dose. Thus, the present study was intended to estimate the first-year doses by extrapolating the Basic Survey results. METHODS: For most municipalities of non-evacuated areas, ambient dose rate had been continuously measured for at least one designated point in each municipality after the accident. In the present study, a municipality-average dose received by residents for a period was assumed to be proportional to the ambient dose measured at the designated point of that municipality during the same period. Based on this assumption, 4-month municipality-average doses calculated from the Basic Survey results were extrapolated to obtain first-year doses. RESULTS: The extrapolated first-year doses for 49 municipalities in the non-evacuated areas had a good correlation with those estimated by UNSCEAR, although the extrapolated doses were generally higher (slope of the regression line: 1.23). The extrapolated municipality-average doses were in reasonable agreement (within 30%) with personal dosimeter measurements, suggesting that the extrapolation was reasonable. CONCLUSION: The present paper reports the first 4-month average doses for all 59 municipalities of Fukushima Prefecture and the extrapolated first-year doses for 49 municipalities. The extrapolated doses will be the basis for future epidemiological studies related to the FHMS.

[Survey of Recognition, Utilization, and Evaluation for Diagnostic Reference Levels in the Field of X-ray Computed Tomography].

A survey on recognition, utilization, and evaluation for diagnostic reference levels (DRLs) after establishing Japan DRLs 2015 in the field of X-ray computed tomography (CT) was conducted for members of Japanese Society of Radiological Technology using web-based questionnaire system. The survey consisted of provincial branches to which respondents belong, their occupation, years of professional experience, years of experience in X-ray CT section, recognition of DRLs, and utilization and evaluation of DRLs in the field of X-ray CT section. Each survey item had one to eight questions. A total of 369 members completed the questionnaire. Among them, 295 out of 369 (79.9%) members knew that DRLs were released in Japan. After establishing the DRLs, 226 of 330 (68.5%) and 123 of 319 (38.6%) members investigated the doses used for adult and pediatric CT at their facilities, respectively. Although 345 of 369 (93.5%) members answered that DRLs are necessary for the field of X-ray CT, only 142 of 369 (38.5%) members thought that the established DRLs are enough to use in the field of X-ray CT. The survey has clarified the current status of recognition, utilization, and evaluation for DRLs in the field of X-ray CT after establishing the DRLs in Japan.

Representativeness of individual external doses estimated for one quarter of residents in the Fukushima Prefecture after the nuclear disaster: the Fukushima Health Management Survey.

After the Fukushima Dai-ichi Nuclear Power Plant accident, the Fukushima Health Management Survey (FHMS) was launched. The Basic Survey, a component of FHMS, is a questionnaire used to survey residents across the Fukushima Prefecture about their behaviour in the first 4 months after the accident. The questionnaire findings are used to determine individual external doses by linking behaviour data to a computer programme with daily gamma ray dose rate maps, drawn after the accident. Through 30 June 2015, the response rate was only 27.2% (558 550 population), indicating that the findings might not be generalisable because of poor representativeness of the population. The objective of this study was to clarify if the data from the FHMS Basic Survey were representative of the entire population, by conducting a new survey to compare the external doses between non-respondents and respondents in the previous survey. A total of 5350 subjects were randomly selected from 7 local regions of Fukushima Prefecture. An interview survey was conducted with the non-respondents to the FHMS Basic Survey. A total of 990 responses were obtained from the previous non-responders by interview survey. For the regions Kempoku, Kenchu, Kennan, Aizu, Minami-Aizu, Soso, and Iwaki, differences in mean effective dose (95% confidence interval) in mSv between the non-responders and previous responders were 0.12 (0.01-0.23), -0.09 (-0.21-0.03), -0.06 (-0.18-0.07), 0.05 (-0.04-0.14), 0.01 (-0.01-0.02), 0.09 (0.01-0.17), 0.09 (0.00-0.17), respectively. The differences fall neither within the interval (-∞, -0.25) nor within the interval (0.25, ∞). These findings imply that mean effective doses between the previous and new respondents were not different, with a significantly indifferent region of 0.25 mSv according to equivalence tests. The present study indicates that the dose distribution obtained from about one-quarter of Fukushima residents represents the dose distribution for the entire Fukushima Prefecture.

Report of IRPA task group on the impact of the eye lens dose limits.

In 2012 IRPA established a task group (TG) to identify key issues in the implementation of the revised eye lens dose limit. The TG reported its conclusions in 2013. In January 2015, IRPA asked the TG to review progress with the implementation of the recommendations from the early report and to collate current practitioner experience. This report presents the results of a survey on the view of the IRPA professionals on the new limit to the lens of the eye and on the wider issue of tissue reactions. Recommendations derived from the survey are presented. This report was approved by IRPA Executive Council on 31 January 2017.

Current situations and discussions in Japan in relation to the new occupational equivalent dose limit for the lens of the eye.

Since the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens of the eye in 2011, there have been extensive discussions in various countries. This paper reviews the current situation in radiation protection of the ocular lens and the discussions on the potential impact of the new lens dose limit in Japan. Topics include historical changes to the lens dose limit, the current situation with occupational lens exposures (e.g., in medical workers, nuclear workers, and Fukushima nuclear power plant workers) and measurements, and the current status of biological studies and epidemiological studies on radiation cataracts. Our focus is on the situation in Japan, but we believe such information sharing will be useful in many other countries.

Nationwide survey of radiation exposure during pediatric computed tomography examinations and proposal of age-based diagnostic reference levels for Japan.

BACKGROUND: Diagnostic reference levels (DRLs) have not been established in Japan. OBJECTIVE: To propose DRLs for CT of the head, chest and abdomen for three pediatric age groups. MATERIALS AND METHODS: We sent a nationwide questionnaire by post to 339 facilities. Questions focused on pediatric CT technology, exposure parameters, CT protocols, and radiation doses for age groups <1 year, 1-5 years, and 6-10 years. RESULTS: For the three age groups in the 196 facilities that responded, the 75th percentile values of volume CT dose index based on a 16-cm phantom (CTDIvol 16 [mGy]) for head, chest and abdominal CT were for infants 39.1, 11.1 and 12.0, respectively; for 1-to 5-year-olds 46.9, 14.3 and 16.7, respectively; and for 6-to 10-year-olds 67.7, 15.0 and 17.0, respectively. The corresponding dose­length products (DLP 16 [mGy・cm]) for head, chest and abdominal CT were for infants 526.1, 209.1 and 261.5, respectively; for 1-to 5-year-olds 665.5, 296.0 and 430.8, respectively; and for 6-to 10-year-olds 847.9, 413.0 and 532.2, respectively. CONCLUSION: The majority of CTDIvol 16 and DLP 16 values for the head were higher than DRLs reported from other countries. For risk reduction, it is necessary to establish DRLs for pediatric CT in Japan.

An influential factor for external radiation dose estimation for residents after the Fukushima Daiichi Nuclear Power Plant accident-time spent outdoors for residents in Iitate Village.

Many studies have been conducted on radiation doses to residents after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Time spent outdoors is an influential factor for external dose estimation. Since little information was available on actual time spent outdoors for residents, different values of average time spent outdoors per day have been used in dose estimation studies on the FDNPP accident. The most conservative value of 24 h was sometimes used, while 2.4 h was adopted for indoor workers in the UNSCEAR 2013 report. Fukushima Medical University has been estimating individual external doses received by residents as a part of the Fukushima Health Management Survey by collecting information on the records of moves and activities (the Basic Survey) after the accident from each resident. In the present study, these records were analyzed to estimate an average time spent outdoors per day. As an example, in Iitate Village, its arithmetic mean was 2.08 h (95% CI: 1.64-2.51) for a total of 170 persons selected from respondents to the Basic Survey. This is a much smaller value than commonly assumed. When 2.08 h is used for the external dose estimation, the dose is about 25% (23-26% when using the above 95% CI) less compared with the dose estimated for the commonly used value of 8 h.

Estimation of Organ and Effective Doses for Neonate and Infant Diagnostic Cardiac Catheterizations.

OBJECTIVE: Radiation exposure to neonates and infants during cardiac catheterizations is an important issue. Smaller patient size and higher heart rate in these patients result in a greater need for magnification modes and higher frame rates, all of which contribute to a significant increase in radiation doses. The aims of our study were to evaluate organ and effective doses for neonates and infants during diagnostic cardiac catheterizations on the basis of in-phantom dosimetry and conversion factors from dose-area product (DAP) to the effective dose. MATERIALS AND METHODS: Organ doses for 0- and 1-year-old children during diagnostic cardiac catheterizations were measured by radiophotoluminescence glass dosimeters implanted in neonate and infant anthropomorphic phantoms. The effective doses were evaluated according to recommendations of the International Commission on Radiologic Protection (ICRP) publication 103. RESULTS: The mean effective doses evaluated according to ICRP 103 were 7.7 mSv (range, 0.1-18.4 mSv) for a neonate and 7.3 mSv (range, 1.9-18.6 mSv) for an infant. Conversion factors from DAP to the effective dose were 2.2 and 4.0 in posteroanterior and lateral cine angiography, respectively, for a neonate and 1.4 and 2.7 in posteroanterior and lateral cine angiography, respectively, for an infant. CONCLUSION: The dose data and conversion factors evaluated in this study could be useful for the estimation of radiation exposure in neonates and infants during diagnostic cardiac catheterization.

[Estimation of Maximum Entrance Skin Dose during Cerebral Angiography].

Using radio-photoluminescence glass dosimeter, we measured the entrance skin dose (ESD) in 46 cases and analyzed the correlations between maximum ESD and angiographic parameters [total fluoroscopic time (TFT); number of digital subtraction angiography (DSA) frames, air kerma at the interventional reference point (AK), and dose-area product (DAP)] to estimate the maximum ESD in real time. Mean (± standard deviation) maximum ESD, dose of the right lens, and dose of the left lens were 431.2 ± 135.8 mGy, 33.6 ± 15.5 mGy, and 58.5 ± 35.0 mGy, respectively. Correlation coefficients (r) between maximum ESD and TFT, number of DSA frames, AK, and DAP were r=0.379 (P<0.01), r=0.702 (P<0.001), r=0.825 (P<0.001), and r=0.709 (P<0.001), respectively. AK was identified as the most useful parameter for real-time prediction of maximum ESD. This study should contribute to the development of new diagnostic reference levels in our country.

[Summary of a survey on radiation exposure during pediatric computed tomography examinations in Japan, focusing on the computed tomography examination environment].

We carried out a nationwide questionnaire survey of pediatric computed tomography (CT) in 339 facilities. Most facilities operated multi detector-row CT (MDCT), and over half operated 64, 128, 256 and 320-slice MDCT. In 32% of facilities, pediatric CT protocols were set taking image quality and dose into consideration. However, in the other facilities, pediatric CT protocols may not be optimized because there is no clear standard for image quality or dosage for pediatric CT examinations in Japan. To promote the optimization of pediatric CT protocols, we regard it as an urgent task to establish diagnostic reference levels for pediatric CT examinations.

Comparison between external and internal doses to the thyroid after the Fukushima Daiichi Nuclear Power Plant accident.

To analyze the association between radiation dose and thyroid cancer after the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, external doses have often been used because of the difficulty to estimate internal thyroid doses individually due to the lack of human data. However, no evaluation has been made as to whether external dose is a good surrogate marker for internal thyroid dose individually. This study aimed at analyzing the relationship between external doses and internal thyroid doses estimated by recently developed methodology. For four municipalities affected by the accident, 200 individuals aged under 20 at the time of the accident per municipality were randomly selected, and their external and internal thyroid doses and their ratios were estimated individually. In a separate analysis, median and arithmetic mean values for external thyroid doses estimated for persons of 16 municipalities that included the above four were compared with those for previously estimated internal thyroid doses. The ratios of the median of internal thyroid dose to that of external thyroid dose in these 16 municipalities ranged from 0.56 to 13.8 for 15-year-old children and 0.91 to 21.1 for 1-year-old children. No consistent relationship between external and internal thyroid doses was found in all 16 municipalities. Thus, thyroid doses from both external and internal exposures should be used to analyze the association between radiation dose and thyroid cancer detection rates for persons who lived in Fukushima Prefecture at the time of the FDNPP accident. (240).

Lessons from past radiation accidents: Critical review of methods addressed to individual dose assessment of potentially exposed people and integration with medical assessment.

The experiences of the Chernobyl and Fukushima nuclear accidents showed that dosimetry was the essential tool in the emergency situation for decision making processes, such as evacuation and application of protective measures. However, at the consequent post-accidental phases, it was crucial also for medical health surveillance and in further adaptation to changed conditions with regards to radiation protection of the affected populations. This review provides an analysis of the experiences related to the role of dosimetry (dose measurements, assessment and reconstruction) regarding health preventive measures in the post-accidental periods on the examples of the major past nuclear accidents such as Chernobyl and Fukushima. Recommendations derived from the review are called to improve individual dose assessment in case of a radiological accident/incident and should be considered in advance as guidelines to follow for having better information. They are given as conclusions.

A multicenter study of radiation doses to the eye lenses of medical staff performing non-vascular imaging and interventional radiology procedures in Japan.

PURPOSE: This study aimed to measure the eye lens doses received by physicians and other medical staff participating in non-vascular imaging and interventional radiology procedures in Japan. MATERIAL AND METHODS: From October 2014 to March 2017, 34 physicians and 29 other medical staff engaged in non-vascular imaging and interventional radiology procedures at 18 Japanese medical facilities. These professionals wore radioprotective lead glasses equipped with small, optically stimulated luminescence dosimeters and additional personal dosimeters at the neck during a 1-month monitoring period. The Hp(3) and the Hp(10) and Hp(0.07) were obtained from these devices, respectively. The monthly Hp(3), Hp(10), and Hp(0.07) for each physician and other medical staff member were then rescaled to a 12-month period to enable comparisons with the revised occupational equivalent dose limit for the eye lens. RESULTS: Among physicians, the average annual Hp(3) values measured by the small luminescence dosimeters on radioprotective glasses were 25.5 ± 38.3 mSv/y (range: 0.4-166.8 mSv/y) and 9.3 ± 16.6 mSv/y (range: 0.3-82.4 mSv/y) on the left and right sides, respectively. The corresponding values for other medical staff were 3.7 ± 3.1 mSv/y (range: 0.4-10.4 mSv/y) and 3.2 ± 2.7 mSv/y (range: 0.5-11.5 mSv/y), respectively. CONCLUSIONS: The eye lens doses incurred by physicians and other medical staff who engaged in non-vascular imaging and interventional radiology procedures in Japan were provided. Physicians should wear radioprotective glasses and use additional radioprotective devices to reduce the amount of eye lens doses they receive.

AGE DEPENDENCE OF INDIVIDUAL EXTERNAL DOSES IN AN EARLY STAGE AFTER THE FUKUSHIMA NUCLEAR ACCIDENT.

Individual external doses for the first 4 months after the Fukushima accident have been estimated by the 'Basic Survey' of the Fukushima Health Management Survey. On the other hand, the UNSCEAR 2013 report presented the first-year effective dose due to external radiation for each municipality in nonevacuated areas of Fukushima Prefecture. In this study, the doses estimated by the Basic Survey were averaged for each of three age groups (infants, 0-5 y; children, 6-15 y; and adults, >16 y), in accordance with the categories adopted by the UNSCEAR report. The average dose ratios (infants/adults and children/adults) obtained from the Basic Survey were 1.08 and 1.06 for nonevacuated areas, respectively. These were smaller than the estimation by the UNSCEAR report (1.7 and 1.4, respectively). Three factors (body size factor, location factor and occupancy factor) were discussed and the location and occupancy factors were likely to be reasons for the difference.

The latest update on individual external doses in an early stage after the Fukushima nuclear accident.

Following the Fukushima Daiichi Nuclear Power Plant accident, a survey for estimating individual external doses for the first 4 months after the accident was started, and it remains ongoing. Since the authors' previous paper, 44 605 new dose estimates have been made. The new dose estimates increase the number of dose estimates to 465 999 and are reported in this note. Since the previous paper, most of the recently collected responses have been gotten through public relations activities to encourage responses across the prefecture. Thus, recent respondents might be biased ('selection bias'). Also, the dose estimates were based on self-administered responses about personal behaviour, which relied on memories of residents. In this respect, incorrect behaviour records possibly resulted as memories have faded over time ('recall bias'). However, the effects of these biases on dose distribution on a whole-prefecture basis seemed to be small.

Effective doses in subjects undergoing computed tomography cardiac imaging with the 256-multislice CT scanner.

BACKGROUND: The 256-multislice CT (256MSCT) obtains volumetric data with 128-mm coverage in a single rotation. This coverage allows satisfactory visualization of the whole heart, allowing the 256MSCT to visualize the cardiac chambers and coronary arteries by cine scan without ECG gating. These characteristics provide a solution to the problems of MSCT. Although a wider beam width provides more efficient imaging over a wider coverage area, patient doses with the 256MSCT are of considerable concern. OBJECTIVE: We assessed potential radiation exposure with the 256MSCT in a cardiac CT protocol and compared the results to those with 16- and 64MSCT (collimated 64x0.5mm using 256MSCT). METHODS: Organ or tissue doses were measured in an anthropomorphic phantom under a coronary artery imaging protocol with the 256MSCT in cine scan mode without ECG gating, and with the 16- and 64MSCT in helical scan mode with ECG gating. RESULTS: Average effective doses were 22.8mSv for the 16MSCT, 27.8mSv for the 64MSCT and 14.1mSv for the 256MSCT. The 16- and 64MSCT doses were thus approximately 1.6- and 2.0-fold higher than those of the 256MSCT. CONCLUSIONS: Use of the 256MSCT in cardiac volumetric cine imaging offers lower radiation exposure than 16- and 64MSCT, and suggests the potential of this equipment in single-beat cardiac imaging without ECG gating. This effective dose is acceptable for routine cardiac imaging.

Patient dose estimation for multi-detector-row CT examinations.

The spread of Multi-detector-row computed tomography (MDCT) has been remarkable. Here, various organ and tissue doses were evaluated with six types of MDCT scanners in common use in Japan; using thermoluminescence dosimeters and anthropomorphic phantoms under condition of routine clinical examinations of the chest in adult and child, of the head in child and of the abdomen-pelvis in adult. Estimated lung doses and averaged effective dose in chest examinations were 19.2 +/- 2.03 mGy and 9.54 +/- 0.90 mSv for the adult and 15.7 +/- 1.88 mGy and 7.42 +/- 0.82 mSv for the child phantom, respectively. The numerical difference between effective dose and organ or tissue doses was about 2-2.5 times. For the adult abdomen-pelvis examinations, averaged effective dose was 13.0 +/- 3.72 mSv. Averaged effective dose for the child head examinations was 2.6 +/- 1.32 mSv. In one case, the dose approached 80 mGy for the brain in the head examination, giving a difference from the effective dose of 10 times or more.

Monte Carlo study of out-of-field exposure in carbon-ion radiotherapy with a passive beam: Organ doses in prostate cancer treatment.

PURPOSE: The aim of this work was to estimate typical dose equivalents to out-of-field organs during carbon-ion radiotherapy (CIRT) with a passive beam for prostate cancer treatment. Additionally, sensitivity analyses of organ doses for various beam parameters and phantom sizes were performed. METHODS: Because the CIRT out-of-field dose depends on the beam parameters, the typical values of those parameters were determined from statistical data on the target properties of patients who received CIRT at the Heavy-Ion Medical Accelerator in Chiba (HIMAC). Using these typical beam-parameter values, out-of-field organ dose equivalents during CIRT for typical prostate treatment were estimated by Monte Carlo simulations using the Particle and Heavy-Ion Transport Code System (PHITS) and the ICRP reference phantom. RESULTS: The results showed that the dose decreased with distance from the target, ranging from 116 mSv in the testes to 7 mSv in the brain. The organ dose equivalents per treatment dose were lower than those either in 6-MV intensity-modulated radiotherapy or in brachytherapy with an Ir-192 source for organs within 40 cm of the target. Sensitivity analyses established that the differences from typical values were within ∼30% for all organs, except the sigmoid colon. CONCLUSIONS: The typical out-of-field organ dose equivalents during passive-beam CIRT were shown. The low sensitivity of the dose equivalent in organs farther than 20 cm from the target indicated that individual dose assessments required for retrospective epidemiological studies may be limited to organs around the target in cases of passive-beam CIRT for prostate cancer.