Medical radiation protection in next decade

Interest in medical radiation protection today is the same as what it would have been almost a century ago. After many decades of relatively safe application of radiation in medicine, the recent spurt in over exposures, over-use of imaging and accidental exposures has created the need for stakeholders to join hands and contribute towards increasing radiation safety levels. Whether it be the need for technological developments to achieve sub-mSv CT scans, tracking of patient exposure history, accounting for repeated exposures of the same patient, specific consideration of requests for radiological examinations that deliver few mSv of dose, or utilization of regulatory approaches, radiological equipment will need to alert users whenever the radiation dose to the patient is above a defined value. The current decade will focus increasingly on carcinogenic effects in patients.     

Estimating cancer risks to adults undergoing body CT examinations

The purpose of the study is to estimate cancer risks from the amount of radiation used to perform body computed tomography (CT) examination. The ImPACT CT Patient Dosimetry Calculator was used to compute values of organ doses for adult body CT examinations. The radiation used to perform each examination was quantified by the dose-length product (DLP). Patient organ doses were converted into corresponding age and sex dependent cancer risks using data from BEIR VII. Results are presented for cancer risks per unit DLP and unit effective dose for 11 sensitive organs, as well as estimates of the contribution from 'other organs'. For patients who differ from a standard sized adult, correction factors based on the patient weight and antero-posterior dimension are provided to adjust organ doses and the corresponding risks. At constant incident radiation intensity, for CT examinations that include the chest, risks for females are markedly higher than those for males, whereas for examinations that include the pelvis, risks in males were slightly higher than those in females. In abdominal CT scans, risks for males and female patients are very similar. For abdominal CT scans, increasing the patient age from 20 to 80 resulted in a reduction in patient risks of nearly a factor of 5. The average cancer risk for chest/abdomen/pelvis CT examinations was ～26 % higher than the cancer risk caused by 'sensitive organs'. Doses and radiation risks in 80 kg adults were ～10 % lower than those in 70 kg patients. Cancer risks in body CT can be estimated from the examination DLP by accounting for sex, age, as well as patient physical characteristics.     

Patient radiation doses in cardiac computed tomography: comparison of published results with prospective and retrospective acquisition

Prospective ECG triggering has the potential of reducing radiation exposure while maintaining diagnostic accuracy of cardiac computed tomography (CT). The aim of this study is to review patient radiation doses associated with coronary artery calcium scoring (CACS) and CT coronary angiography (CTCA) and to compare results between prospective and retrospective acquisition schemes. Patient radiation doses from CACS and CTCA were extracted from 67 relevant studies. Mean effective dose for CACS and CTCA with prospective ECG triggering is significantly lower than retrospective acquisition, 0.9±0.4 vs. 3.1±1.4 mSv, p < 0.001, and 3.4±1.4 vs. 11.1±5.4 mSv, p < 0.001, respectively. In both cardiac CT examinations, application of dose modulation techniques result in significantly lower doses in retrospective schemes, however, even with dose modulation, retrospective acquisition is associated with significantly higher doses than prospective acquisition. The number of slices acquired per rotation and the number of X-ray sources of the CT scanner (single or dual source) do not have a significant effect on patient dose.     

Current status of patient radiation doses from computed tomography examinations in Tanzania

The aim of this study was to assess the magnitude of radiation dose imparted to patients undergoing CT (computed tomography) examinations in Tanzania. The effective doses to patients undergoing five common CT examinations were obtained from eight health centres. The doses to patients were estimated using measurements of CTDI, exposure-related parameters and the CTDOSE software based on NRPB conversion factors. The mean effective doses in Tanzania for CT examinations of head, lumbar spine, chest, abdomen and pelvis were 2.2+/-0.9, 5.4+/-2.3, 12.2+/-3.4, 15.3+/-6.0 and 13.4+/-7.3 mSv, respectively. The mean effective doses and the variations in dose between hospitals in Tanzania were mostly comparable with reported values in the literature for six different countries from Europe. The observed wide variation in mean effective dose for similar CT examination among hospitals was largely influenced by different CT scanning protocols employed among hospitals. In view of the observed causes of variation in patient doses, it was concluded that further studies are needed to investigate the methods that can reduce dose to patients without affecting image quality.     

Occupational exposures of Chinese medical radiation workers in 1986-2000

Data on occupational exposures from medical uses of radiation in China during 1986-2000 are presented. Individual dose monitoring results in the reports of monitoring centres in different provinces in China during 1986-2000 were collected as the basic data. These data were summarised and then analysed. From 1986 to 2000, in diagnostic radiology, nuclear medicine and radiotherapy, the annual collective effective doses varied within the range 122.4-206.6, 5.4-9.3 and 4.1-10.3 man Sv, respectively; the average annual effective dose in these categories varied within the range 1.5-2.2, 1.2-1.6 and 1.0-1.5 mSv, respectively. Almost all the average annual effective doses in medical uses of radiation were <3 mSv in 1986-2000, and no monitored workers were found to have received an occupational exposure >50 mSv in a single year or >100 mSv in a 5-y period. After 1990, the protection status of medical radiation workers in China was sufficient.     

Utilisation of PACS to monitor patient CT doses

In the past 5 y, the number of computed tomography (CT) studies has doubled at Dubai Health Authority hospitals. This situation, along with patient's overdoses reported internationally, has prompted action to establish a system to manage patient doses incurred due to medical imaging practices. In this work, the authors aim to homogenise dose reporting to monitor radiation dose levels and facilitate the establishment of local and national dose reference levels. The two hospitals enrolled in this study are equipped with three CT systems (two 4 slices and one 64 slices). Through the Picture Archive and Communication Systems (PACS) tracking system, it is mandatory to fill CT patient doses in radiology information system (RIS). Dose length product (mGy cm) was recorded for 2502 adult and 178 paediatric patients. All patients' dosimetry data were collected from the RIS by Cogonos statistical software. The PACS data were reviewed to exclude incomplete data. Average and range of effective doses for adult and paediatric patients were calculated using an appropriate weighting factor. Individual accumulated effective doses for adult and paediatric patients were calculated for 4s-scanner-1 only. Adult average effective doses for the head (1482 exams) were 1.23 ± 0.58, 2.84 ± 0.83 and 2.98 ± 1.103 mSv, the chest (545 exams) were 5.39 ± 1.63, 21.85 ± 5.63 and 18.19 ± 3.22 mSv and for the abdomen and pelvis (1183 exams) were 10.85 ± 4.26, 25.66 ± 8.83 and 26.46 ± 13.75 mSv for 4s-scanner-1, 4s-scanner-2 and 64 s, respectively. The paediatric average effective dose for the head (127 exams) was 1.77 ± 0.82 mSv, for the chest (22 exams) was 3.3 ± 1.29 mSv and for the abdomen and pelvis (27 exams) was 6.16 ± 2.64 mSv. Results of individual accumulated effective doses for adult and paediatric patients were presented. PACS dose reporting facilitated dosimetry clinical auditing. Effective doses obtained in this work demonstrated that the results of one scanner were within the international dose levels while the other two scanners were higher. Technical actions are recommended to standardise the dose levels.     

Mammographic screening: is the benefit worth the risk?

Justification of medical exposures is a fundamental principle of radiation protection. This principle applies to mammographic screening, both for the screened population and at an individual level. The benefit of mammographic screening may be considered to be the number of cancers detected or lives saved by breast screening. The risk is the hypothetical number of fatal cancers induced by the use of ionising radiation in screening mammography. Benefit can be deduced from the cancer detection rate in the NHS Breast Screening Programme. The number of additional lives saved by the intervention of a screening programme may be deduced from knowledge of the change in tumour size, stage and nodal status (and hence prognosis) in women with screening detected breast cancers compared with symptomatic women before screening. Calculations of benefit risk ratios to the UK population have been performed. It is concluded that breast screening is justified in radiation protection terms.     

Dose level of occupational exposure in China

This paper discusses the dose level of Chinese occupational exposures during 1986-2000. Data on occupational exposures from the main categories in nuclear fuel cycle (uranium enrichment and conversion, fuel fabrication, reactor operation, waste management and research activity, except for uranium mining and milling because of the lack of data), medical uses of radiation (diagnostic radiation, nuclear medicine and radiotherapy) and industrial uses of radiation (industrial radiography and radioisotope production) are presented and summarised in detail. These are the main components of occupational exposures in China. In general, the average annual effective doses show a steady decreasing trend over periods: from 2.16 to 1.16 mSv in medical uses of radiation during 1990-2000; from 1.92 to 1.18 mSv in industrial radiography during 1990-2000; from 8.79 to 2.05 mSv in radioisotope production during the period 1980-2000. Almost all the average annual effective doses in discussed occupations were lower than 5 mSv in recent years (except for well-logging: 6.86 mSv in 1999) and no monitored workers were found to have received the occupational exposure exceeding 50 mSv in a single year or 100 mSv in a five-year period. So the Chinese protection status of occupation exposure has been improved in recent years. However, the average annual effective doses in some occupations, such as diagnostic radiology and coal mining, were still much higher than that of the whole world. There are still needs for further improvement and careful monitoring of occupational exposure to protect every worker from excessive occupational exposure, especially for the workers who were neglected before.     

Radiation protection for accompanying person and radiation workers in PET/CT

The purposes of the present study are to measure the total radiation doses for the radiation workers and for the accompanying person to the patients in positron emission tomography (PET)/computed tomography (CT) imaging. Urines samples from the patients were collected at 43, 62, 87, 117, 238, 362 min after the 555-MBq (18)flour-fluorodeoxyglucose ((18)F-FDG) injection and activities were measured. Dose rates were recorded using a Geiger-Muller counter and the total radiation doses were measured with using an electronic personnel dosemeter. According to the results here, 18.4 % of (18)F-FDG was excreted in the urine in 117 min after injection. At 117th min after injection, dose rates were determined as 345, 220, 140, 50 and 15 μSv h(-1), at proposed distances. The radiation doses after 117 min were measured as 3.92 mSv at 0.1 m, 2.11 mSv at 0.25 m and 1.08 mSv at 0.5 m. In conclusion, radiation protection will be sufficient within 2 h after (18)F-FDG injection for PET/CT imaging in daily practice.     

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.     

Justification in clinical radiological practice: a survey among staff of five London hospitals

This study represents a survey performed among staff who, according to the Ionising Radiation (Medical Exposures) Regulations of 2000 (IRMER), are responsible for justifying radiological examinations in the UK. The aim of the survey is to map the current situation regarding knowledge of risks from X-ray exposures and the criteria used for their justification. An anonymous electronic questionnaire was emailed to 219 radiologists and radiographers of five National Health Service hospitals. The questions were designed to investigate the way the sample group defines/assesses risk and benefit when justifying medical exposures, and to test their knowledge on radiation doses, risk communication, and on relevant national legislation. The majority of the respondents are aware of the relevant legislation/guidelines. Patient's medical condition, age and sex, and alternative techniques using less or no ionising radiation are the main criteria used for justification. However, when estimating the effective dose of various examinations in chest radiograph equivalents, the majority of the responses were incorrect. Although there is good knowledge of legislation around justification of medical exposures, there seems to be a lack of knowledge on radiation doses and risks among IRMER practitioners.     

Patient dose during radiological examination in the follow-up of bariatric surgery

A patient dose survey was carried out measuring the kerma-area product (KAP) values during radiological evaluation in the follow-up of bariatric surgery. The procedures were performed by three radiologists to adjust laparoscopic gastric bands and to detect postoperative complications after Roux-en-Y gastric bypass procedures to treat morbid obesity. Total fluoroscopy time, exposure factors and the overall contribution of fluoroscopy to the accumulated KAP value were recorded. The median KAP values were used to estimate organ doses and effective dose to a standard patient; the radiation risk associated with the procedures was also evaluated. The doses were smaller for one of the three radiologists, owing to a more appropriate beam collimation and a reduction of the screening time. The KAP values ranged from 1.6 to 7.1 Gy cm(2) for the laparoscopic adjustable gastric banding management, and from 3.0 and 8.3 Gy cm(2) for the radiological examinations after gastric bypass. As a whole, the effective doses associated to these procedures were between 0.5 and 2.7 mSv. The organs receiving the highest doses were not only breast, stomach, pancreas and liver, but also lungs, owing to of their high radiosensitivity, significantly contributed to the effective dose.     

Radiation exposure assessment for portsmouth naval shipyard health studies

Occupational radiation exposures of 13,475 civilian nuclear shipyard workers were investigated as part of a retrospective mortality study. Estimates of annual, cumulative and collective doses were tabulated for future dose-response analysis. Record sets were assembled and amended through range checks, examination of distributions and inspection. Methods were developed to adjust for administrative overestimates and dose from previous employment. Uncertainties from doses below the recording threshold were estimated. Low-dose protracted radiation exposures from submarine overhaul and repair predominated. Cumulative doses are best approximated by a hybrid log-normal distribution with arithmetic mean and median values of 20.59 and 3.24 mSv, respectively. The distribution is highly skewed with more than half the workers having cumulative doses <10 mSv and >95% having doses <100 mSv. The maximum cumulative dose is estimated at 649.39 mSv from 15 person-years of exposure. The collective dose was 277.42 person-Sv with 96.8% attributed to employment at Portsmouth Naval Shipyard.     

Radiation doses to patients undergoing barium meal and barium enema examinations

The radiation doses received by patients during 41 barium meal (BM) and 42 barium enema (BE) examinations in two Greek hospitals are presented. Radiation dose was measured in terms of the dose area product (DAP). The effective dose and doses to certain organs were estimated using the ODS-60 software. Mean total DAP values were found to be 25 +/- 11 Gy cm2 for BM and 60 +/- 35 Gy cm2 for BE examinations, whereas the estimated mean values of effective dose were 8.6 +/- 4.0 and 24 +/- 16 mSv respectively. DAP to effective dose conversion coefficients were estimated to be 0.34 mSv per Gy cm2 for BM and 0.41 mSv per Gy cm2 for BE.     

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.     

First results on patient dose measurements from conventional diagnostic radiology procedures in Serbia and Montenegro

The objective of this work is to assess patient doses for the most frequent X-ray examinations for the first time in Serbia and Montenegro. A total of 510 procedures for 11 different examination categories in 3 general hospitals were analysed. Mean and median entrance surface air kerma (ESAK) and kerma area product (KAP) values followed by mean effective doses were reported. Using X-ray tube output data, ESAK for each radiographic examination was calculated, as well as the effective dose for each patient. Except for chest PA examination, all estimated doses are less than stated European and International Atomic Energy Agency (IAEA) reference levels for simple radiographic examinations. For complex examinations involving fluoroscopy and radiography total KAP was measured and contributions from fluoroscopy and radiography were assessed. The study of KAP confirms that the dose level for complex fluoroscopy investigations is closely related to the technique and individual patient variation in terms of fluoroscopy time and number of radiography exposures. The obtained values are comparable to those reported in the UK. Survey data are aimed aid development of a national quality control and radiation protection programme for medical exposures.     

Organ dose evaluation for multi-slice spiral CT scans based on China Sichuan chest anthropomorphic phantom measurements

The authors measured organ radiation doses during multi-slice computed tomography (MSCT) chest scans using a China Sichuan anthropomorphic phantom (CDP-1C). Chest CT images from live volunteers based on automatic tube current modulation (ATCM) techniques were similar to those obtained using the CDP-1C phantom, indicating that the phantom accurately modelled the anatomic structure and X-ray absorbance of the human torso. Indeed, attenuation values differed by <5%. Organ radiation doses were measured using thermoluminescence dosemeters in the CDP-1C. With increased noise index, the CT dose index, the dose-length product and the average organ dose all decreased. Thus, the CDP-1C phantom can also assess dose levels during CT examinations in Chinese patients. The noise index (based on ATCM techniques) should be set to 8.5 or higher to reduce X-ray exposure while maintaining appropriate resolution for diagnosis.     

Transition in occupational radiation exposure monitoring methods in diagnostic and interventional radiology

Radiation exposure monitoring is a traditional keystone of occupational radiation safety measures in medical imaging. The aim of this study was to review the data on occupational exposures in a large central university hospital radiology organisation and propose changes in the radiation worker categories and methods of exposure monitoring. An additional objective was to evaluate the development of electronic personal dosimeters and their potential in the digitised radiology environment. The personal equivalent dose of 267 radiation workers (116 radiologists and 151 radiographers) was monitored using personal dosimeters during the years 2006-2010. Accumulated exposure monitoring results exceeding the registration threshold were observed in the personal dosimeters of 73 workers (59 radiologists' doses ranged from 0.1 to 45.1 mSv; 14 radiographers' doses ranged from 0.1 to 1.3 mSv). The accumulated personal equivalent doses are generally very small, only a few angiography radiologists have doses >10 mSv per 5 y. The typical effective doses are <10 μSv y(-1) and the highest value was 0.3 mSv (single interventional radiologist). A revised categorisation of radiation workers based on the working profile of the radiologist and observed accumulated doses is justified. Occupational monitoring can be implemented mostly with group dosimeters. An active real-time dosimetry system is warranted to support radiation protection strategy where optimisation aspects, including improving working methods, are essential.     

CT dosimetry computer codes: their influence on radiation dose estimates and the necessity for their revision under new ICRP radiation protection standards

Computed tomography (CT) dosimetry computer codes have been most commonly used due to their user friendliness, but with little consideration for potential uncertainty in estimated organ dose and their underlying limitations. Generally, radiation doses calculated with different CT dosimetry computer codes were comparable, although relatively large differences were observed for some specific organs or tissues. The largest difference in radiation doses calculated using different computer codes was observed for Siemens Sensation CT scanners. Radiation doses varied with patient age and sex. Younger patients and adult females receive a higher radiation dose in general than adult males for the same CT technique factors. There are a number of limitations of current CT dosimetry computer codes. These include unrealistic modelling of the human anatomy, a limited number of organs and tissues for dose calculation, inability to alter patient height and weight, and non-applicability to new CT technologies. Therefore, further studies are needed to overcome these limitations and to improve CT dosimetry.