Patient dose measurements in radiological practices

Internationally agreed standards for radiation measurements applied to medicine underpin the application of scientific methods to both therapeutic and diagnostic radiological practices. Equally it is recommended that these standards should underpin radiation measurements within the fields of nuclear energy and industrial applications of ionizing radiations. Such measurements should also apply to all exposed groups: patients, workers and members of the general public. It would appear that the underlying philosophy as well as measurement methods, including units, employed in the therapeutic and diagnostic domains have developed separately and independently over the past 30 years. Similarly, although radiological imaging methods are fundamental to both domains, a similar situation appears to apply to the assessment of image quality. This letter attempts to highlight the present situation regarding the role and relevance of dosimetric methods applied in both therapeutic and diagnostic radiological practices. In particular the present situation is discussed in relation to the primary objectives of the International Commission on Radiological Units and Measurements (ICRU). Scope for harmonization and unification of scientific methods applied in therapy and diagnosis is highlighted.     

工业射线装置建设项目放射防护控制效果评价

目的 对某单位的3类工业射线装置(14台)建设项目进行放射防护控制效果评价,以保障放射工作人员的健康与安全.方法 依据国家相关法律、法规和标准,通过对工作场所和射线装置进行放射防护检测,结合该单位提交的有关材料,综合评价该建设项目的放射防护控制效果.结果 该单位从事3类工业射线装置的放射工作人员受到的年有效剂量均低于5 mSv,既满足建设单位放射工作人员年有效剂量5 mSv的目标管理值,又满足国家规定的放射工作人员年有效剂量要求.该工业射线装置建设项目的各项防护指标均符合GB 18871-2002和《放射性同位素与射线装置安全和防护条例》等法律法规以及该单位管理目标的要求.结论 该工业射线装置建设项目能有效控制放射性职业病的危害因素,辐射防护设施满足竣工要求,同时该建设单位应加强培训,提高放射性工作人员的自我保护意识,确保建设项目在实际运行时能够顺利进行.     

Estimation of genome damage after exposure to ionizing radiation and ultrasound used in industry

The application of ionizing radiation in industry for nondestructive testing entails a specific framework of working conditions that include field work, facilities with different radioactive sources, maintenance thereof without halting production, use of nonionizing radiation, and exposure to chemical agents. The present study gives an estimation of recent genome damage in two groups of subjects using chromosome aberration assay and micronucleus assay. The first group was exposed to (192)Ir and the second was simultaneously exposed to (192)Ir and ultrasound. The results show that both groups had higher values of chromosome aberrations and micronucleus frequency than controls. The group of examinees exposed both to (192)Ir and ultrasound had significantly more chromatid breaks, acentric fragments, and dicentric chromosomes, and had a significantly higher frequency of micronuclei than subjects exposed to (192)Ir only. The study suggests that the detected differences in the genome damage may be attributed to the action of ultrasound. This study confirms the dosimetry data for ionizing radiation, which indicate that the methods used in industrial radiography and the usage of nonionizing radiation entail an increased health risk. In the absence of personal dosimeters for nonionizing radiation and chemical agents, biomonitoring provides reliable parameters for estimation of genome damage and may lead to improvements in working conditions and radiation safety programs.     

Application of the MAX/EGS4 exposure model to the dosimetry of the Yanango radiation accident

According to the International Atomic Energy Agency (IAEA), industrial radiography accounts for approximately half of all reported accidents for the nuclear related industry. Detailed information about these accidents have been published by the IAEA in its Safety Report Series, one of which describes the radiological accident which happened in 1999 in Yanango/Peru. Under unsettled circumstances an 192Ir source was lost from an industrial radiographic camera and later picked up by a welder, who normally had nothing to do with the radiographic work. The man put the source into the right back pocket of his jeans and continued working for at least another 6.5 h. This study uses the MAX/EGS4 exposure model in order to determine absorbed dose distributions in the right thigh of the MAX phantom, as well as average absorbed doses to radiosensitive organs and tissues. For this purpose, the Monte Carlo code for standard exposure situations has been modified in order to match the irradiation conditions of the accident as closely as possible. The results present the maximum voxel absorbed dose, voxel depth absorbed dose and voxel surface absorbed dose distributions, average organ and tissue doses and a maximum surface absorbed dose for zero depth.     

Chromosomal aberration analysis in chronically exposed radiation workers.

We performed a chromosomal aberration analysis on blood samples of 15 radiation workers by scoring dicentric aberrations. These workers were chronically exposed to cumulative doses of approximately 500 mSv over a period of two to three decades. The biological doses estimated using the linear coefficient of the in vitro dose/response curve based on dicentric frequency varied from 0 to 259 mGy, even though all the radiation workers had received approximately the same physical dose--i.e., 500 mSv. In all cases of chronic exposure, the estimated biological doses were found to be lower than the measured physical doses. The measured physical doses were corrected by applying the biphasic decay pattern of lymphocytes and also taking into consideration the time course of accumulation of doses in each individual. The corrected physical doses thus obtained were then compared with the estimated biological doses, and a reasonably good correlation was found between these two sets of values. However, on the whole, the corrected physical doses were found to be smaller than the estimated biological doses in most of the cases. This observation suggests that the kinetics of turnover of lymphocytes in conditions of chronic exposure may be slower than estimated so far in various studies involving exposures to high doses, wherein the estimation of life span of lymphocytes was carried out in patients undergoing radiotherapy.     

The alkaline Comet assay as biomarker in assessment of DNA damage in medical personnel occupationally exposed to ionizing radiation

The alkaline Comet assay was selected as a biomarker of exposure to evaluate the ongoing exposure to ionizing radiation of 50 medical workers occupationally exposed to ionizing radiation and 50 corresponding unexposed control subjects. The primary DNA damage was evaluated by measuring the extent of DNA migration in peripheral blood leukocytes. The inter-individual differences in DNA damage between exposed subjects were compared with their dosimeter readings and occupation. It was found that medical workers who were occupationally exposed to ionizing radiation for different periods of time showed highly significant increases in levels of DNA damage compared with controls. However, influences of the different occupational settings and doses absorbed on the levels of DNA damage, assessed by use of the Comet assay, might be excluded in the majority of subjects. Differences in comet parameters measured due to smoking and gender were not statistically significant in either exposed or control subjects. The results obtained have confirmed the usefulness of the alkaline Comet assay as an additional complement to standard biodosimetric methods. By detection of momentary DNA damage and/or repair activity, it reflects the concurrent exposure and the actual levels of DNA damage present in peripheral blood leukocytes of the radiological workers at the moment of blood sampling.     

Evaluation of chromosomal aberrations, micronuclei, and sister chromatid exchanges in hospital workers chronically exposed to ionizing radiation.

Cytogenetic analysis was performed in peripheral blood lymphocytes from hospital workers chronically exposed to ionizing radiation in comparison to matched non-exposed individuals. The accumulated absorbed doses calculated for the radiation workers ranged from 9.5 to 209.4 mSv. The endpoints used were chromosomal aberrations (CA), micronuclei (MN), and sister chromatid exchanges (SCE). The frequencies of CA/100 cells observed for the exposed group were significantly (P=0.018) higher than in the control group: 3.2 and 2.6, respectively. Similarly, the mean numbers of SCE per cell were statistically higher (P=0.025) in the exposed group (6.2) in comparison with the control group (5.8). In the case of micronuclei analysis, no significant (P=0,06) difference between both groups was found, but these data should be cautiously interpreted since an increase in the frequencies of MN was found for radiation workers (3.0 MN/100 cells), compared to the control group (2.6 MN/100 cells) and this increase occur in parallel to CA and SCE frequencies. The difference between the results could be explained by the nature of CA and MN generation. The increased frequencies of CA and SCE in radiation workers indicate the cumulative effect of low-level chronic exposure to ionizing radiation, and the relevance of conducting cytogenetic analysis in parallel to physical dosimetry in the working place.     

Increased hprt mutant frequencies in Brazilian children accidentally exposed to ionizing radiation

We have examined the effects of ionizing radiation on somatic mutations in vivo, using the hprt clonal assay. The study was performed on blood samples obtained from children exposed during a radiological accident that happened in 1987, in Goiânia, Brazil. The group of children exposed to ionizing radiation includes six males and four females ranging in age from 6 to 14 years at the time of exposure. The radiation doses ranged from 15 to 70 cGy. A Brazilian control group, not exposed to ionizing radiation, was also analyzed under similar conditions. The mean hprt mutant frequency for the exposed group was 4.6 times higher than the control group, although the cloning efficiency from the exposed group was significantly reduced. Linear regression analysis of the mutant frequency and ionizing radiation dose did not show a significant relationship between these two parameters. However, a reliable inverse relationship was demonstrated when the regression analysis was performed with nonselective cloning efficiency and ionizing radiation dose. It was demonstrated that nonselective cloning efficiency diminishes as ionizing radiation dose increases. To correct mutant frequencies for clonal events, the clonal relationship between the hprt mutant clones was examined by T-cell receptor analysis. The majority of the mutants analyzed represented individual clones, thus validating the observed mutant frequencies. © 1996 Wiley-Liss, Inc.     

Normalized conceptus doses for abdominal radiographic examinations calculated using a Monte Carlo technique

The aim of the present study was to develop a reliable method for estimating conceptus radiation doses resulting from abdominal radiographic examinations for all trimesters of pregnancy. The method is based on normalized conceptus doses estimated using Monte Carlo modeling. The Monte Carlo N-Particle (MCNP) radiation transport code was employed in the current study. The validity of the MCNP computational approach was verified by comparison with dose data obtained in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation using thermoluminescence dosimetry (TLD). The results consist of radiation doses normalized to air kerma so that conceptus dose from any technique and x-ray unit used for abdominal radiography can be easily calculated. Normalized conceptus doses are presented for the first, second, and third trimesters of gestation for various kVp and total beam filtration values. Data apply to radiographic systems equipped with high frequency or 3 phase 12 pulse generators. A very good agreement was observed between the normalized conceptus doses estimated by TLD measurements and the MCNP simulation for all periods of gestation (maximum difference 8.1%). The results of MCNP procedures were compared to published data obtained by TLD measurements. Normalized conceptus dose values agree well, with most differences being lower than 10%. The normalized doses obtained in the current study are dependent on field size. However, for small changes in the size of the x-ray field, the change in normalized doses is not considerable. Accurate estimation of conceptus doses due to abdominal conventional x-ray examinations can be made using the dose data provided in the current study.     

The micronucleus assay as a biological dosimeter of in vivo ionising radiation exposure

Biological dosimetry, based on the analysis of micronuclei (MN) in the cytokinesis-block micronucleus (CBMN) assay can be used as an alternative method for scoring dicentric chromosomes in the field of radiation protection. Biological dosimetry or Biodosimetry, is mainly performed, in addition to physical dosimetry, with the aim of individual dose assessment. Many studies have shown that the number of radiation-induced MN is strongly correlated with dose and quality of radiation. The CBMN assay has become, in the last years, a thoroughly validated and standardised technique to evaluate in vivo radiation exposure of occupational, medical and accidentally exposed individuals. Compared to the gold standard, the dicentric assay, the CBMN assay has the important advantage of allowing economical, easy and quick analysis. The main disadvantage of the CBMN assay is related to the variable micronucleus (MN) background frequency, by which only in vivo exposures in excess of 0.2-0.3 Gy X-rays can be detected. In the last years, several improvements have been achieved, with the ultimate goals (i) of further increasing the sensitivity of the CBMN assay for low-dose detection by combining the assay with a fluorescence in situ hybridisation centromere staining technique, (ii) of increasing the specificity of the test for radiation by scoring nucleoplasmic bridges in binucleated cells and (iii) of making the assay optimally suitable for rapid automated analysis of a large number of samples, viz. in case of a large-scale radiation accident. The development of a combined automated MN-centromere scoring procedure remains a challenge for the future, as it will allow systematic biomonitoring of radiation workers exposed to low-dose radiation.     

Medical examination of the workers occupationally exposed to ionizing radiation

The hazardous effects of ionizing radiation to man are well recognized, and they are divided into two groups, the stochastic effects (hereditary and carcinogenic effect) and non-stochastic effects (somatic effects such as depression of hematopoiesis, chronic dermatitis and cataracta). The basic framework of the International Commission on Radiological Protection (ICRP) is intended to prevent the occurrence of non-stochastic effects, by keeping doses below the relevant thresholds, and to ensure that all reasonable aspects are taken to reduce the incidence of stochastic effects. In Japan, the regulatory provisions of radiological protection of the workers occupationally exposed to ionizing radiation are based on the recommendation of ICRP adopted in 1977. According to these regulations, the dose equivalent limits of occupational exposure of man has been decided at 50 mSv/year. The monitoring of exposure to the individual and the procedure of medical examination of the workers are briefly described and discussed.     

Organ doses from environmental exposures calculated using voxel phantoms of adults and children

This paper presents effective and organ dose conversion coefficients for members of the public due to environmental external exposures, calculated using the ICRP adult male and female reference computational phantoms as well as voxel phantoms of a baby, two children and four adult individual phantoms--one male and three female, one of them pregnant. Dose conversion coefficients are given for source geometries representing environmental radiation exposures, i.e. whole body irradiations from a volume source in air, representing a radioactive cloud, a plane source in the ground at a depth of 0.5?g?cm(-2), representing ground contamination by radioactive fall-out, and uniformly distributed natural sources in the ground. The organ dose conversion coefficients were calculated employing the Monte Carlo code EGSnrc simulating the photon transport in the voxel phantoms, and are given as effective and equivalent doses normalized to air kerma free-in-air at height 1?m above the ground in Sv Gy(-1). The findings showed that, in general, the smaller the body mass of the phantom, the higher the dose. The difference in effective dose between an adult and an infant is 80-90% at 50?keV and less than 40% above 100?keV. Furthermore, dose equivalent rates for photon exposures of several radionuclides for the above environmental exposures were calculated with the most recent nuclear decay data. Data are shown for effective dose, thyroid, colon and red bone marrow. The results are expected to facilitate regulation of exposure to radiation, relating activities of radionuclides distributed in air and ground to dose of the public due to external radiation as well as the investigation of the radiological effects of major radiation accidents such as the recent one in Fukushima and the decision making of several committees.     

Survey of radiological techniques and doses of children undergoing some common x-ray examinations in three hospitals in Nigeria

A dosimetric survey has been carried out in order to investigate typical radiation doses for children undergoing a number of common x-ray examinations in Nigeria. The results presented in this work are derived from the data of 226 children from three different hospitals included in the survey. Assuming the sample is representative of national practice patterns, pediatric chest examinations are the most frequent radiological examinations. Doses were measured by attaching thermoluminescent dosimeters to the patient's skin to determine entrance surface dose (ESD). The mean and standard deviation of the individual ESD values are reported. Comparisons were made between these doses and diagnostic reference levels, and also between the doses and those from other countries. The mean ESD values in the present work are found to be generally higher than those found in an UNSCEAR document and the NRPB diagnostic reference levels. The ratio of maximum ESD to minimum ESD, a parameter that characterizes ESD variation, was found to be less than 10 in each of the hospitals, while across the three hospitals the ratio was found to be greater than 10. The reasons for the high mean ESD and the variations in patients' ESD values have been discussed in terms of regulatory control, personnel, difference in radiological techniques, performance of x-ray facility, film processing condition, and the type of film-screen combination used. The results presented in this work will form part of the baseline data needed for deriving national guidance levels of pediatric radiological examination. In addition, it will also serve as a source of additional information on pediatric patient dosimetry. Suggestions are given on how to reduce doses to pediatric patients during x-ray examinations, especially in developing countries.     

Absorption spectra analysis of exposed FWT-60 radiochromic film

The visible absorption spectra of Radiachromic FWT-60 radiochromic film have been investigated to analyse the dosimetry characteristics of the film. The film is radiation sensitive to high absorbed doses. The visible absorption spectra of this film when exposed to photon radiation show a peak at 605 nm which is stable over the dose range of 0 Gy to 20 kGy. The radiation sensitive absorption spectra are present over the wavelength range of approximately 500 nm to 660 nm. Negligible dose response is seen in the infrared region or the UV region of wavelength readout. Variation of sensitivity of response can be achieved by varying the wavelength of readout with the maximum measured response of 0.077 OD units per kGy. The film can be an ideal dosimeter for areas where high dose levels need to be measured.     

Advances in the treatment of chronic myeloid leukemia

Fortunately radiation accidents are infrequent occurrences, but since they have the potential of large scale events like the nuclear accidents of Chernobyl and Fukushima, preparatory planning of the medical management of radiation accident victims is very important. Radiation accidents can result in different types of radiation exposure for which the diagnostic and therapeutic measures, as well as the outcomes, differ. The clinical course of acute radiation syndrome depends on the absorbed radiation dose and its distribution. Multi-organ-involvement and multi-organ-failure need be taken into account. The most vulnerable organ system to radiation exposure is the hematopoietic system. In addition to hematopoietic syndrome, radiation induced damage to the skin plays an important role in diagnostics and the treatment of radiation accident victims. The most important therapeutic principles with special reference to hematopoietic syndrome and cutaneous radiation syndrome are reviewed.     

Comparison of four methods for assessing patient effective dose from radiological examinations

Three methods of indirect effective dose estimation were reviewed and compared to a direct effective dose determination method. An anthropomorphic phantom and thermoluminescence dosimetry were used to obtain dosimetric data associated with anterior-posterior (AP) abdominal radiography, posterior-anterior (PA) chest radiography, PA head radiography, and AP heart fluoroscopy. Effective dose was determined using: (i) organ specific dose values directly determined by thermoluminescence dosimeters, (ii) data published by National Radiological Protection Board (NRPB) and entrance surface dose (ESD), (iii) NRPB data and dose area product (DAP), (iv) energy imparted derived from DAP. The effective dose values estimated from the Rando phantom measurements were 161, 32.3, and 8.4 microSv/projection for the abdomen, chest, and head radiographs, respectively. Cardiac fluoroscopy yielded an effective dose value of 111 microSv/min. The effective dose values obtained indirectly using NRPB data and DAP were in good agreement with directly assessed values in all simulated exposures (difference <8%). The effective doses using NRPB data and ESD values differed from directly assessed values by less than 15% for the radiographic exposures and 60% for heart fluoroscopy. The energy imparted method yielded 136, 31, and 6.6 microSv/projection for the abdomen, chest, and head radiographs, respectively, and 111 microSv/min for heart fluoroscopy. Indirect patient effective dose determination using the NRPB dosimetric data and the measured value of incident radiation allows for reliable patient effective dose estimates. The use of DAP rather than ESD is recommended because it yields accurate results even for complex radiologic exposures involving fluoroscopy. The value of energy imparted may be used for the accurate determination of patient effective dose, especially when specific organ dose values are not of interest. The calculation of energy imparted with the use of EAP provides a reliable starting point for estimation of effective dose from radiologic examinations for which dosimetric data are not provided by NRPB.     

Stable and unstable chromosome aberrations measured after occupational exposure to ionizing radiation and ultrasound

Aim

To evaluate chromosome aberration and fluorescent in situ hybridization (FISH) assays as a method to estimate of health risk, we monitored 9 male subjects occupationally exposed to low doses of both ionizing radiation and ultrasound during a period of over 3 years.

Methods

Sampling was performed at 6-month intervals during a three-year period. First we used conventional chromosomal aberrations analysis. When the aberration frequency for a particular subject reached the background, we measured translocations in the final sample, using fluorescence in situ hybridization. Chromosome painting probes for chromosomes 1, 2, and 4 were used simultaneously.

Results

Dicentric and ring chromosomes were eliminated within a year. Translocations persisted and deviated from control values in all examinees. Translocations were detected long after unstable aberrations decreased to the background level.

Conclusion

Fluorescence in situ hybridization-based translocation detection was a reliable method for monitoring chronic occupational clastogen exposure. Chromosome aberration assay correlated with translocation frequency. Stable chromosomal aberrations reflected cumulative genome damage during job exposure.For the last 30 years, chromosome aberration assay and detection of unstable aberrations, dicentrics and acentric fragments, have been used for the estimation of genome damage caused by physical and chemical clastogens (1). Since physical dosimetry provides only limited information when it comes to complex exposures, biodosimetry has increasingly gained in importance. The introduction of ultrasound in medicine and industrial technology has made the evaluation of genome damage more complicated due to absence of personal dosimetry and still undefined mechanisms of its clastogenic and aneugenic potentials.The scientific importance of dicentric chromosome detection is significant. Biodosimetry based on dicentric calculations improved radiation protection and supplied data on the correlation between genome damage and other biomarkers related to ionizing radiation exposure, such as hematological parameters or development of neoplasms (1,2). However, a false perception was created that a decrease in the frequency of dicentrics means that the health-risk has disappeared.There is a need for reliable methods to assess past exposure to clastogens and the related risk. This is particularly the case for a large number of individuals exposed to various levels of ionizing radiation caused by nuclear accidents such as Chernobyl, atmospheric nuclear testing prior to the early 1960s, the atomic bombing at Hiroshima and Nagasaki, various medical radiological procedures, and occupational exposures for which dosimetric information may be poor or absent (3,4). Our study focused principally on the application and evaluation of a technology referred to as “chromosome painting” for investigating human exposure at workplace and its risk assessment. This technology employs the method of fluorescence in situ hybridization (FISH) with whole chromosome probes, which rapidly and accurately detect stable chromosome abnormalities, such as translocations, in individuals exposed in the past (5-8).The aim of our study was to compare the use of chromosomal aberrations and FISH method in the evaluation of health risk in individuals occupationally exposed to low doses of ionizing radiation and ultrasound in industry over long periods time, by biomonitoring the results of unstable and stable chromosome aberrations     

Facial trauma in the largest city in Latin America, São Paulo, 15 years after the enactment of the compulsory seat belt law

Traffic accidents are a reality throughout Brazil. The face is one of the anatomic parts most affected by these accidents, especially when a seat belt is not used. These accidents are costly for the public health system and have a significant impact on society and the lives of families involved. The compulsory use of seat belts in Brazil, especially in São Paulo, has decreased the rate of facial trauma. This suggests that the public health policies and measures adopted by the Brazilian authorities have benefited the population 15 years after the enactment of the law of compulsory seat belts in the city of São Paulo.     

In vivo dosimetry for estimation of effective doses in multislice CT coronary angiography

In vivo dosimetry represents a technique that has been widely employed to evaluate the dose to the patient mainly in radiotherapy. Considering the increment in dose to the population due to new high-dose multislice CT examinations, such as coronary angiography, it is becoming important to more accurately know the dose to the patient. The desire to know patient dose extends even to radiological examinations. Thermoluminescent dosimeters are considered the gold standard for in vivo dosimetry, but their use is time consuming. A rapid, less labor-intensive method has been developed to perform in vivo dosimetry using radiochromic film positioned next to the patient's skin. Multislice CT scanners allow the estimation of the effective dose to the patient from the dose length product (DLP) parameter, the value of which is displayed on the acquisition console, simply multiplying the DLP by published conversion factors. The method represents only an approximation based on standard size circular phantoms and neglects the actual size of the patient. More accurate evaluations can be carried out using software-based Monte Carlo simulations. However, these methods do not consider possible dose reduction techniques, such as automatic tube-current modulation. For 22 patients effective doses measured by in vivo dosimetry and calculated by software were compared. The technique of using in vivo dosimetry measured with radiochromic film appears a promising procedure for improving the assessment of the effective dose to the patient.