The state of the art in the 1990's: NCRP Report No. 136 on the scientific bases for linearity in the dose-response relationship for ionizing radiation

Redox dysregulation in imaging professionals occupationally exposed to ionizing and non-ionizing radiation

Purpose: Imaging professionals are occupationally exposed to chronic ionizing radiation (IR) and non-ionizing radiation (NIR). This study aimed to investigate the influence of occupational radiation exposure on oxidative stress and antioxidant levels based on blood biomarkers in different hospital imaging professional groups.Materials and methods: The study groups included 66 imaging professionals occupationally exposed to IR (n = 58, 43 diagnostic radiography (G1), seven nuclear medicine (G2), eight radiation therapy (G3)), and NIR (n = 8, ultrasound imaging (G4)) and 60 non-exposed controls. Blood levels of superoxide (O2•-) as an index of oxidative stress, and the antioxidant activities of superoxide dismutase (SOD), glutathione ratio (GSH/GSSG), and catalase (CAT) were measured.Results: The blood values of O2•-, SOD, and CAT were significantly higher in imaging professionals occupationally exposed to radiation than in the control group (p < .05), while a significant decrease in the ratio of GSH/GSSG was observed (p < .05). The results from the NIR group were significantly higher compared to IR group.Conclusions: Based on these results, chronic exposure to radiation (IR and NIR) is associated with redox dysregulation that may result in damages to cellular biomolecules including lipids, proteins and DNA. Further studies are needed to determine the impact of redox dysregulation and the need for periodic examination among imaging professionals occupationally exposed to IR and NIR.

The Long-Term Impact of Ionizing Radiation on DNA Damage in Patients Undergoing Multiple Cardiac Catheterizations

Ionizing radiation (IR) exposures have increased exponentially in recent years due to the rise in diagnostic and therapeutic interventions. A number of small-scale studies investigated the long-term effect of IR on health workers or immediate effects of IR on patients undergoing catheterization procedures; however, the long-term impact of multiple cardiac catheterizations on DNA damage on a patient population is not known. In this study, the effects of IR on DNA damage, based on micronuclei (MN) frequency and 8-hydroxy-2'-deoxyguanosine (8-OHdG) as markers in peripheral lymphocytes, were evaluated in patients who previously underwent multiple cardiac catheterization procedures. Moreover, genetic polymorphisms in genes PARP1 Val762Ala, OGG1 Ser326Cys, and APE1 Asn148Glu as a measure of sensitivity to radiation exposure were also investigated in the same patient population. The patients who underwent ≥ 3 cardiac catheterization procedures revealed higher DNA injury in comparison to the patients who underwent ≤ 2 procedures, documented with the presence of higher level of MN frequency (6.4 ± 4.8 vs. 9.1 ± 4.3, p = 0.002) and elevated serum 8-OHdG levels (33.7 ± 3.8 ng/mL vs. 17.4 ± 1.9 ng/mL, p = 0.001). Besides, OGG1 Ser326Cys and APE1 Asn148Glu heterozygous and homozygous polymorphic types, which are related with DNA repair mechanisms, were significantly associated with MN frequency levels (p = 0.006 for heterozygous and p = 0.001 for homozygous with respect to OGG1 Ser326Cys, p = 0.007 for heterozygous and p = 0.001 for homozygous with respect to APE1 Asn148Glu). There was no significant difference in terms of PARP1 Val762Ala gene polymorphism between two groups.

2022 KLCA-NCC Korea practice guidelines for the management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the fourth most common cancer among men in South Korea, where the prevalence of chronic hepatitis B infection is high in middle and old age. The current practice guidelines will provide useful and sensible advice for the clinical management of patients with HCC. A total of 49 experts in the fields of hepatology, oncology, surgery, radiology, and radiation oncology from the Korean Liver Cancer Association-National Cancer Center Korea Practice Guideline Revision Committee revised the 2018 Korean guidelines and developed new recommendations that integrate the most up-to-date research findings and expert opinions. These guidelines provide useful information and direction for all clinicians, trainees, and researchers in the diagnosis and treatment of HCC.

2022 KLCA-NCC Korea Practice Guidelines for the Management of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the fourth most common cancer among men in South Korea, where the prevalence of chronic hepatitis B infection is high in middle and old age. The current practice guidelines will provide useful and sensible advice for the clinical management of patients with HCC. A total of 49 experts in the fields of hepatology, oncology, surgery, radiology, and radiation oncology from the Korean Liver Cancer Association-National Cancer Center Korea Practice Guideline Revision Committee revised the 2018 Korean guidelines and developed new recommendations that integrate the most up-to-date research findings and expert opinions. These guidelines provide useful information and direction for all clinicians, trainees, and researchers in the diagnosis and treatment of HCC.

Minimal Detectable Width of Tooth Fractures Using Magnetic Resonance Imaging and Method to Measure

INTRODUCTION

Vertical root fracture (VRF) in root canal-treated (RCT) teeth is a common cause of pain, bone resorption, and tooth loss. VRF is also difficult to diagnose and measure. Magnetic resonance imaging (MRI) has the potential to identify VRF due to beneficial partial volume averaging, without using ionizing radiation. This investigation aimed to describe the narrowest VRFs detectable based on MRI, using micro-computed tomography (microCT) as the reference standard and proposes a method using profile integrals to measure the widths of small VRFs.

METHODS

VRFs were induced in 62 RCT tooth root samples. All samples were imaged in a phantom using MRI and reference imaging was obtained using microCT. The stacks of 3-dimensional axial MRIs were assessed by 3 board-certified endodontists. Evaluators determined the most coronal slice within the stack that was discernible as the extent of the VRF. This slice was measured on correlated microCT sections to determine the minimum VRF width (μm) detectable using a profile integral-based method to measure small fractures and negate the effects of the point spread function.

RESULTS

Using profile integrals to measure VRF width was repeatable and resulted in estimates that were on average 1 μm smaller than known reference widths. Adjusted median VRF width detected using MRI was 45 μm (first quartile: 26 μm, third quartile: 64 μm).

CONCLUSION

Using profile integrals is a valid way to estimate small VRF width. The MRI approach demonstrated ability to repeatedly detect VRFs as small as 26 μm.

2022 KLCA-NCC Korea practice guidelines for the management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the fourth most common cancer among men in South Korea, where the prevalence of chronic hepatitis B infection is high in middle and old age. The current practice guidelines will provide useful and sensible advice for the clinical management of patients with HCC. A total of 49 experts in the fields of hepatology, oncology, surgery, radiology, and radiation oncology from the Korean Liver Cancer Association-National Cancer Center Korea Practice Guideline Revision Committee revised the 2018 Korean guidelines and developed new recommendations that integrate the most up-to-date research findings and expert opinions. These guidelines provide useful information and direction for all clinicians, trainees, and researchers in the diagnosis and treatment of HCC.

Cephalometry without complex dedicated postprocessing in an oriented magnetic resonance imaging dataset: a pilot study

OBJECTIVES

Magnetic resonance imaging (MRI) enables a 3D-volume-imaging without ionizing radiation. Therefore, it was the aim of this study to present a post-processing-free method for cephalometric analysis of a MRI-dataset and to examine whether there is a significant difference between cephalometric analysis of conventional 2D cephalograms and MRI scans.

METHODS

One MRI scan each was performed on three cadaver heads using a 3T-MR-scanner. Cephalometric analysis was conducted directly on the 3D dataset. All reference points were projected onto a virtual sagittal plane that was perpendicular to the Frankfort horizontal plane. Double-sided points were averaged. Cephalometric angles were measured from the projected points. Results were compared with cephalometric measurements on conventional lateral cephalometric radiographs (LCRs). The cephalometric analysis was performed by five raters.

RESULTS

390-angle measurements were obtained. The inter-rater reliability was high [intraclass correlation coefficients (ICCs) ≥ 0.74 for all angles]. Differences between the measurements on the cephalograms and MRI scans ranged between -0.91° (-1.88°, 0.07°) and 0.97° (-0.63°, 2.57°) on average and were equivalent with respect to a margin of [-2°, 2°] in all angles except L1-Me-Tgo (Bonferroni-Holm-corrected P < 0.05 in all angles except L1-Me-Tgo). The best match was found for the SNA angle.

CONCLUSION

The clinical comparability of the MRI- and LCR-based cephalometry could be stated. Using MRI in orthodontics would reduce radiation exposure and the risk of stochastic radiation damage, which is of importance especially in younger patients.

Organ Doses, Effective Dose, and Cancer Risk From Coronary CT Angiography Examinations

OBJECTIVE. The purposes of this study were to determine organ and effective doses and to estimate the risk of exposure-induced cancer death (REID) associated with coronary CT angiography (CCTA) examinations. SUBJECTS AND METHODS. CCTA examinations were performed in three stages: calcium score, monitoring, and cardiac phases for all patients. Effective dose was calculated using two methods. The first was based on the scanner-derived dose-length product, and the second entailed use of an organ and effective dose calculator software application. Organ doses were calculated on the basis of the tissue weighting factors of International Commission on Radiation Protection report 103. REID values were assessed with a cancer risk estimator software application. RESULTS. The study included 185 patients (95 men, 90 women). For women, breast doses were high at 52.04 ± 14.08 mGy. The mean effective dose in the women was greater than that in the men (24.05 vs 16.30 mSv, p < 0.05). The mean REID values in patients undergoing CCTA with a 64-MDCT scanner were 13.4 per 10,000 men (1 in 746) and 19.6 per 10,000 women (1 in 508). The REID values were considerably higher for the younger women. CONCLUSION. The results of this study will help referring physicians justify requesting CCTA examinations by considering their benefits for diagnosis on the one hand and awareness of the risk of radiation-induced cancer on the other. In the case of CCTA scans that are properly justified by clinical indication, patients and physicians should not be concerned about the radiation risks.

2018 Korean Liver Cancer Association-National Cancer Center Korea Practice Guidelines for the Management of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer globally and the fourth most common cancer in men in Korea, where the prevalence of chronic hepatitis B infection is high in middle-aged and elderly patients. These practice guidelines will provide useful and constructive advice for the clinical management of patients with HCC. A total of 44 experts in hepatology, oncology, surgery, radiology, and radiation oncology in the Korean Liver Cancer Association-National Cancer Center Korea Practice Guideline Revision Committee revised the 2014 Korean guidelines and developed new recommendations that integrate the most up-to-date research findings and expert opinions.

The risk of cancer attributable to diagnostic medical radiation: Estimation for France in 2015

Although medical ionizing radiation (IR) has clear clinical benefits, it is an established carcinogen. Our study estimates the number of new cancer cases in France in 2015 attributable to IR exposure from medical procedures. Exposures from external (X-rays, CT scans, interventional radiology) and internal (nuclear medicine) sources were considered. We used 2007 national frequencies of diagnostic examinations by sex and age to estimate the lifetime organ dose exposure adjusted for changes in the use of such procedures over time. The Biological Effects of Ionizing Radiation VII risk models were used to estimate the corresponding excess cancer risk, assuming an average latency period of 10 years. Additionally, we used cancer incidence data from the French Cancer Registries Network. Of the 346,000 estimated new cancer cases in adults in France in 2015, 2300 cases (940 among men and 1360 among women) were attributable to diagnostic IR, representing 0.7% of all new cancer cases (0.5% for men and 0.9% for women). The leading cancers attributable to medical IR were female breast (n = 560 cases), lung (n = 500 cases) and colon (n = 290 cases) cancers. Compared to other risk factors, the contribution of medical IR to the cancer burden is small, and the benefits largely outweigh its harms. However, some of these IR-associated cancer cases may be preventable through dose optimization of and enhanced justification for diagnostic examinations.

2018 Korean Liver Cancer Association-National Cancer Center Korea Practice Guidelines for the Management of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer globally and the fourth most common cancer in men in Korea, where the prevalence of chronic hepatitis B infection is high in middle-aged and elderly patients. These practice guidelines will provide useful and constructive advice for the clinical management of patients with HCC. A total of 44 experts in hepatology, oncology, surgery, radiology and radiation oncology in the Korean Liver Cancer Association-National Cancer Center Korea Practice Guideline Revision Committee revised the 2014 Korean guidelines and developed new recommendations that integrate the most up-to-date research findings and expert opinions.

Classical radiation biology dogma, bystander effects and paradigm shifts

A classical dogma of radiation biology asserts that all effects of radiation on cells are due to it's direct, immediate actions. But evidence accumulated over the last 50 years shows that radiation also has, indirect ‘non-target’ actions including ‘bystander’ effects in which effects of radiation on cells or media are transported to cells or tissues that were not ‘hit’ by the radiation, leading to changes in their function. This important but heretical recognition of radiation actions has been referred to, probably incorrectly, as a ‘paradigm shift.’ What these signals are and how they induce changes is not well understood. Also not clear is how, or if, bystander effects might affect risk estimates for exposure to low doses of radiation. These issues are reviewed and explored in this series of papers.

Effective dose of dental CBCT-a meta analysis of published data and additional data for nine CBCT units

OBJECTIVES

This article analyses dose measurement and effective dose estimation of dental CBCT examinations. Challenges to accurate calculation of dose are discussed and the use of dose-height product (DHP) as an alternative to dose-area product (DAP) is explored.

METHODS

The English literature on effective dose was reviewed. Data from these studies together with additional data for nine CBCT units were analysed. Descriptive statistics, ANOVA and paired analysis are used to characterize the data.

RESULTS

PubMed and EMBASE searches yielded 519 and 743 publications, respectively, which were reduced to 20 following review. Reported adult effective doses for any protocol ranged from 46 to 1073 µSv for large fields of view (FOVs), 9-560 µSv for medium FOVs and 5-652 µSv for small FOVs. Child effective doses from any protocol ranged from 13 to 769 µSv for large or medium FOVs and 7-521 µSv for small FOVs. Effective doses from standard or default exposure protocols were available for 167 adult and 52 child exposures. Mean adult effective doses grouped by FOV size were 212 µSv (large), 177 µSv (medium) and 84 µSv (small). Mean child doses were 175 µSv (combined large and medium) and 103 µSv (small). Large differences were seen between different CBCT units. Additional low-dose and high-definition protocols available for many units extend the range of doses. DHP was found to reduce average absolute error for calculation of dose by 45% in comparison with DAP.

CONCLUSIONS

Large exposure ranges make CBCT doses difficult to generalize. Use of DHP as a metric for estimating effective dose warrants further investigation.

2014 KLCSG-NCC Korea Practice Guideline for the Management of Hepatocellular Carcinoma

The guideline for the management of hepatocellular carcinoma (HCC) was first developed in 2003 and revised in 2009 by the Korean Liver Cancer Study Group and the National Cancer Center, Korea. Since then, many studies on HCC have been carried out in Korea and other countries. In particular, a substantial body of knowledge has been accumulated on diagnosis, staging, and treatment specific to Asian characteristics, especially Koreans, prompting the proposal of new strategies. Accordingly, the new guideline presented herein was developed on the basis of recent evidence and expert opinions. The primary targets of this guideline are patients with suspicious or newly diagnosed HCC. This guideline provides recommendations for the initial treatment of patients with newly diagnosed HCC.

2014 Korean Liver Cancer Study Group-National Cancer Center Korea practice guideline for the management of hepatocellular carcinoma

The guideline for the management of hepatocellular carcinoma (HCC) was first developed in 2003 and revised in 2009 by the Korean Liver Cancer Study Group and the National Cancer Center, Korea. Since then, many studies on HCC have been carried out in Korea and other countries. In particular, a substantial body of knowledge has been accumulated on diagnosis, staging, and treatment specific to Asian characteristics, especially Koreans, prompting the proposal of new strategies. Accordingly, the new guideline presented herein was developed on the basis of recent evidence and expert opinions. The primary targets of this guideline are patients with suspicious or newly diagnosed HCC. This guideline provides recommendations for the initial treatment of patients with newly diagnosed HCC.

Comparison of cancer risk associated with low-dose ionizing radiation from cardiac imaging and therapeutic procedures after acute myocardial infarction in women versus men

Patients with cardiovascular disease are increasingly exposed to low-dose ionizing radiation (LDIR) from diagnostic and therapeutic procedures. Previous studies have suggested that the malignancy risk associated with LDIR may be greatest in women and in young patients. We sought to compare the effect of LDIR on incident cancer across gender and age strata in a population-based cohort of patients with myocardial infarction (MI). All initially cancer-free patients with MI from 1996 to 2006 were identified in a province-wide administrative database. Procedure-specific LDIR dose estimates were used to generate a cumulative cardiac LDIR exposure variable. Time-dependent multivariate Cox regression was used to determine the relation between cardiac LDIR and incident cancer. A time-lag covariate of 3 years was used wherein a de novo cancer could only be attributed to LDIR incurred at least 3 years earlier. The effect of age and gender on LDIR-associated risk of cancer was evaluated with stratified models and the addition of interaction terms. The study cohort consisted of 56,606 men and 26,255 women. For each millisievert of cardiac LDIR, women were more likely to develop a cancer (hazard ratio 1.005, 95% confidence interval 1.002 to 1.008) than men (hazard ratio 1.002, 95% confidence interval 1.001 to 1.004) after adjusting for age, noncardiac LDIR, and covariates (p for interaction = 0.014). Contrarily, over the range studied (predominantly patients aged >50 years), age was not a determinant of LDIR-associated risk of cancer. In conclusion, women exposed to LDIR from cardiac imaging and therapeutic procedures after MI are at a greater risk of incident cancer compared with men after similar exposure. The extrapolated absolute risk from LDIR exposure would nonetheless be expected to be low.

Computed tomography for pulmonary embolism: assessment of a 1-year cohort and estimated cancer risk associated with diagnostic irradiation

BACKGROUND

The principal concern of any radiation exposure in computed tomography (CT) is the induction of stochastic risks of developing a radiation-induced cancer. The results given in this manuscript will allow to (re-)calculate yield of chest CT.

PURPOSE

To demonstrate a method to evaluate the lifetime attributable risk (LAR) of cancer incidence/mortality due to a single diagnostic investigation in a 1-year cohort of consecutive chest CT for suspected pulmonary embolism (PE).

MATERIAL AND METHODS

A 1-year cohort of consecutive chest CT for suspected PE using a standard scan protocol was analyzed retrospectively (691 patients, 352 men, 339 women). Normalized patient-specific estimations of the radiation doses received by individual organs were correlated with age- and sex-specific mean predicted cancer incidence and age- and sex-specific predicted cancer mortality based on the BEIR VII results. Additional correlation was provided for natural occurring risks.

RESULTS

LAR of cancer incidence/mortality following one chest CT was calculated for cancer of the stomach, colon, liver, lung, breast, uterus, ovaries, bladder, thyroid, and for leukemia. LAR remains very low for all age and sex categories, being highest for cancer of the lungs and breasts in 20-year-old women (0.61% and 0.4%, respectively). Summation of all cancer sites analyzed raised the cumulative relative LAR up to 2.76% in 20-year-old women.

CONCLUSION

Using the method presented in this work, LAR of cancer incidence and cancer mortality for a single chest CT for PE seems very low for all age groups and both sexes, but being highest for young patients. Hence the risk for radiation-induced organ cancers must be outweighed with the potential benefit or a treatment and the potential risks of a missed and therefore untreated PE.

Effects of radiation and vitamin C treatment on metronidazole genotoxicity in mice

The impact of exposure to low dose radiation (LDR) on human health is not clear. Besides, cross adaptation or sensitization with pharmaceutical agents may modify the risk of LDR. In the present study, we analyzed the interaction of radiation and metronidazole (MTZ) in inducing chromosome aberration (CA) and micronucleus (MN) in the bone marrow cells of Balb/C mice in vivo. Further, we evaluated the efficacy of vitamin C to reduce MTZ induced genotoxicity. We found that 10, 20 and 40mg/kg of MTZ induced dose dependent increase in the frequency of CA (r=0.9923, P<0.01) as well as MN (r=0.9823, P<0.05) in polychromatic erythrocytes. However, MTZ did not affect the ratio of polychromatic erythrocytes to normochromatic erythrocytes indicating lack of cytotoxicity. Supplementation with vitamin C prior to MTZ treatment significantly reduced the frequency of CA (P<0.001) as well as MN (P<0.001). Radiation (0.5Gy) exposure prior to MTZ treatment produced a less than additive (for CA) to additive (for MN) effects. However, radiation exposure following MTZ treatment produced additive (for CA) and synergistic (for MN) effects. Further, vitamin C pre-treatment also reduced the genotoxicity indices following the combined treatment of MTZ and radiation. Our findings suggest that MTZ may sensitize bone marrow cells to radiation exposure and enhances genotoxicity. We recommend more studies on the interaction of LDR and marketed pharmaceuticals to minimize possible harmful outcomes through appropriate precautionary measures.

Dose response of micronuclei induced by combination radiation of α-particles and γ-rays in human lymphoblast cells

Combination radiation is a real situation of both nuclear accident exposure and space radiation environment, but its biological dosimetry is still not established. This study investigated the dose-response of micronuclei (MN) induction in lymphocyte by irradiating HMy2.CIR lymphoblast cells with α-particles, γ-rays, and their combinations. Results showed that the dose-response of MN induced by γ-rays was well-fitted with the linear-quadratic model. But for α-particle irradiation, the MN induction had a biphasic phenomenon containing a low dose hypersensitivity characteristic and its dose response could be well-stimulated with a state vector model where radiation-induced bystander effect (RIBE) was involved. For the combination exposure, the dose response of MN was similar to that of α-irradiation. However, the yield of MN was closely related to the sequence of irradiations. When the cells were irradiated with α-particles at first and then γ-rays, a synergistic effect of MN induction was observed. But when the cells were irradiated with γ-rays followed by α-particles, an antagonistic effect of MN was observed in the low dose range although this combination radiation also yielded a synergistic effect at high doses. When the interval between two irradiations was extended to 4h, a cross-adaptive response against the other irradiation was induced by a low dose of γ-rays but not α-particles.

The balance between initiation and promotion in radiation-induced murine carcinogenesis

Studies of radiation carcinogenesis in animals allow detailed investigation of how the risk depends on age at exposure and time since exposure and of the mechanisms that determine this risk, e.g., induction of new pre-malignant cells (initiation) and enhanced proliferation of already existing pre-malignant cells (promotion). To assist the interpretation of these patterns, we apply a newly developed biologically based mathematical model to data on several types of solid tumors induced by acute whole-body radiation in mice. The model includes both initiation and promotion and analyzes pre-malignant cell dynamics on two different time scales: comparatively short-term during irradiation and long-term during the entire life span. Our results suggest general mechanistic similarities between radiation carcinogenesis in mice and in human atomic bomb survivors. The excess relative risk (ERR) in mice decreases with age at exposure up to an exposure age of 1 year, which corresponds to mid-adulthood in humans; the pattern for older ages at exposure, for which there is some evidence of increasing ERRs in atomic bomb survivors, cannot be evaluated using the data set analyzed here. Also similar to findings in humans, initiation dominates the ERR at young ages in mice, when there are few background pre-malignant cells, and promotion becomes important at older ages.

A new view of radiation-induced cancer: integrating short- and long-term processes. Part II: second cancer risk estimation

As the number of cancer survivors grows, prediction of radiotherapy-induced second cancer risks becomes increasingly important. Because the latency period for solid tumors is long, the risks of recently introduced radiotherapy protocols are not yet directly measurable. In the accompanying article, we presented a new biologically based mathematical model, which, in principle, can estimate second cancer risks for any protocol. The novelty of the model is that it integrates, into a single formalism, mechanistic analyses of pre-malignant cell dynamics on two different time scales: short-term during radiotherapy and recovery; long-term during the entire life span. Here, we apply the model to nine solid cancer types (stomach, lung, colon, rectal, pancreatic, bladder, breast, central nervous system, and thyroid) using data on radiotherapy-induced second malignancies, on Japanese atomic bomb survivors, and on background US cancer incidence. Potentially, the model can be incorporated into radiotherapy treatment planning algorithms, adding second cancer risk as an optimization criterion.

Bystander effect and adaptive response in C3H 10T½ cells

PURPOSE

To address the relationship between the bystander effect and the adaptive response that can compete to impact on the dose-response curve at low doses.

MATERIALS AND METHODS

A novel radiation apparatus, where targeted and non-targeted cells were grown in close proximity, was used to investigate these phenomena in C3H 10T(1/2) cells. It was further examined whether a bystander effect or an adaptive response could be induced by a factor(s) present in the supernatants of cells exposed to a high or low dose of X-rays, respectively.

RESULTS

When non-hit cells were co-cultured for 24 h with cells irradiated with 5 Gy alpha-particles, a significant increase in both cell killing and oncogenic transformation frequency was observed. If these cells were treated with 2 cGy X-rays 5 h before co-culture with irradiated cells, approximately 95% of the bystander effect was cancelled out. A 2.5-fold decrease in the oncogenic transformation frequency was also observed. When cells were cultured in medium donated from cells exposed to 5 Gy X-rays, a significant bystander effect was observed for clonogenic survival. When cells were cultured for 5 h with supernatant from donor cells exposed to 2 cGy and were then irradiated with 4 Gy X-rays, they failed to show an increase in survival compared with cells directly irradiated with 4 Gy. However, a twofold reduction in the oncogenic transformation frequency was seen.

CONCLUSIONS

An adaptive dose of X-rays cancelled out the majority of the bystander effect produced by alpha-particles. For oncogenic transformation, but not cell survival, radioadaption can occur in unirradiated cells via a transmissible factor(s).

Mammography-oncogenecity at low doses

Controversy exists regarding the biological effectiveness of low energy x-rays used for mammography breast screening. Recent radiobiology studies have provided compelling evidence that these low energy x-rays may be 4.42 +/- 2.02 times more effective in causing mutational damage than higher energy x-rays. These data include a study involving in vitro irradiation of a human cell line using a mammography x-ray source and a high energy source which matches the spectrum of radiation observed in survivors from the Hiroshima atomic bomb. Current radiation risk estimates rely heavily on data from the atomic bomb survivors, and a direct comparison between the diagnostic energies used in the UK breast screening programme and those used for risk estimates can now be made. Evidence highlighting the increase in relative biological effectiveness (RBE) of mammography x-rays to a range of x-ray energies implies that the risks of radiation-induced breast cancers for mammography x-rays are potentially underestimated by a factor of four. A pooled analysis of three measurements gives a maximal RBE (for malignant transformation of human cells in vitro) of 4.02 +/- 0.72 for 29 kVp (peak accelerating voltage) x-rays compared to high energy electrons and higher energy x-rays. For the majority of women in the UK NHS breast screening programme, it is shown that the benefit safely exceeds the risk of possible cancer induction even when this higher biological effectiveness factor is applied. The risk/benefit analysis, however, implies the need for caution for women screened under the age of 50, and particularly for those with a family history (and therefore a likely genetic susceptibility) of breast cancer. In vitro radiobiological data are generally acquired at high doses, and there are different extrapolation mechanisms to the low doses seen clinically. Recent low dose in vitro data have indicated a potential suppressive effect at very low dose rates and doses. Whilst mammography is a low dose exposure, it is not a low dose rate examination, and protraction of dose should not be confused with fractionation. Although there is potential for a suppressive effect at low doses, recent epidemiological data, and several international radiation risk assessments, continue to promote the linear no-threshold (LNT) model. Finally, recent studies have shown that magnetic resonance imaging (MRI) is more sensitive than mammography in detecting invasive breast cancer in women with a genetic sensitivity. Since an increase in the risk associated with mammographic screening would blur the justification of exposure for this high risk subgroup, the use of other (non-ionising) screening modalities is preferable.

Radiation dose and cancer risk estimates in 16-slice computed tomography coronary angiography

BACKGROUND

Recent advances have led to a rapid increase in the number of computed tomography coronary angiography (CTCA) studies performed. Whereas several studies have reported the effective dose, there are no data available on cancer risk for current CTCA protocols.

METHODS AND RESULTS

Effective and organ doses were estimated, by use of scanner-derived parameters and Monte Carlo methods, for 50 patients having 16-slice CTCA performed for clinical indications. Lifetime attributable risks were estimated with models developed in the National Academies' Biological Effects of Ionizing Radiation VII report. The effective dose of a complete CTCA averaged 9.5 mSv, whereas that of a complete study, including calcium scoring when indicated, averaged 11.7 mSv. Calcium scoring increased effective dose by 25%, whereas tube current modulation reduced it by 34% and was more effective at lower heart rates. Organ doses to the lungs and female breast were highest. The lifetime attributable risk of cancer incidence from CTCA averaged approximately 1 in 1,600 but varied widely among patients, being highest in younger women. For all patients, the greatest risk was from lung cancer.

CONCLUSIONS

CTCA is associated with non-negligible risk of malignancy. Doses can be reduced by careful attention to scanning protocol.

Shift in imaging modalities of gastrointestinal tract through 25 years and its impact on patient ionizing radiation doses

We wanted to explore the shift in modalities when diagnosing the gastrointestinal tract through the last three decades and see how this has influenced on the radiation doses given to this patient population. Activity reports from a central hospital in the years of 1979-2003 have been reviewed. The x-ray based modalities have decreased, while there has been a marked increase in colonoscopies, gastroscopies, ultrasound, and magnetic resonance cholangiopancreatography. This has caused a reduction in collective effective radiation dose of 54%.

Cytogenetic effect of low dose gamma-radiation in Hordeum vulgare seedlings: non-linear dose-effect relationship

The induction of chromosome aberrations in Hordeum vulgare germinated seeds was studied after ionizing irradiation with doses in the range of 10-1,000 mGy. The relationship between the frequency of aberrant cells and the absorbed dose was found to be nonlinear. A dose-independent plateau in the dose range from about 50 to 500 mGy was observed, where the level of cytogenetic damage was significantly different from the spontaneous level. The comparison of the goodness of the experimental data fitting with mathematical models of different complexity, using the most common quantitative criteria, demonstrated the advantage of a piecewise linear model over linear and polynomial models in approximating the frequency of cytogenetical disturbances. The results of the study support the hypothesis of indirect mechanisms of mutagenesis induced by low doses. Fundamental and applied implications of these findings are discussed.

Shift in imaging modalities of the urinary tract over a 25-year period and its impact on ionizing radiation doses given to patients

OBJECTIVES

To explore the shift in imaging modalities used when examining the urinary tract over the period 1979-2003 and to see how this shift, together with a radiation protection policy, have influenced the doses of ionizing radiation used.

MATERIAL AND METHODS

Activity reports from a department of radiology were reviewed. Relevant radiation dose estimates were obtained from the Norwegian Radiation Protection Authority.

RESULTS

Ultrasound (US) was introduced in 1983 and has been increasingly used since then. MRI was introduced in 1992 and has been used to some extent when examining the urinary tract. The use of i.v. pyelography decreased by 50% during the review period and the use of plain radiographs remained practically unchanged. The number of CT examinations increased until 1983, but decreased thereafter. The total number of examinations of the urinary tract has increased during the review period, but the radiation doses given have decreased.

CONCLUSIONS

The introduction of US and MRI, together with a radiation protection policy, have reduced the ionizing radiation doses given to this population, in spite of an increase in the total number of examinations of the urinary tract.

Shift in imaging modalities of the spine through 25 years and its impact on patient ionizing radiation doses

STUDY DESIGN

Retrospective.

OBJECTIVE

To explore the shift in modalities when diagnosing the spine in the years 1979-2003. To see how this shift, together with a radiation protective policy, have influenced on the ionizing radiation doses.

SUMMARY OF BACKGROUND DATA

The shift from CT/myelography to MR when diagnosing the spine is well known. To what extent this has changed the radiation doses has to our knowledge not yet been published.

METHODS

Activity reports from a department of radiology have been reviewed. Relevant radiation doses estimates have been obtained from the Norwegian Radiation Protection Authority.

RESULTS

MRI was introduced in 1992 and has been used increasingly since then. Conventional X-ray to the spine has been practically unchanged. Myelography and CT decreased markedly after the introduction of MRI. The total number of examinations of the spine has increased, but the radiation doses given have decreased since 1993.

CONCLUSIONS

The introduction of MRI together with a radiation protective policy have reduced the ionizing radiation doses given to this population, in spite of an increase in the total number of examinations of the spine.

Low doses of radiation are protective in vitro and in vivo: evolutionary origins

Research reports using cells from bacteria, yeast, alga, nematodes, fish, plants, insects, amphibians, birds and mammals, including wild deer, rodents or humans show non-linear radio-adaptive processes in response to low doses of low LET radiation. Low doses increased cellular DNA double-strand break repair capacity, reduced the risk of cell death, reduced radiation or chemically-induced chromosomal aberrations and mutations, and reduced spontaneous or radiation-induced malignant transformation in vitro. In animals, a single low, whole body dose of low LET radiation, increased cancer latency and restored a portion of the life that would have been lost due to either spontaneous or radiation-induced cancer in the absence of the low dose. In genetically normal fetal mice, a prior low dose protected against radiation-induced birth defects. In genetically normal adult-male mice, a low dose prior to a high dose protected the offspring of the mice from heritable mutations produced by the large dose. The results show that low doses of low-LET radiation induce protective effects and that these induced responses have been tightly conserved throughout evolution, suggesting that they are basic responses critical to life. The results also argue strongly that the assumption of a linear increase in risk with increasing dose in humans is unlikely to be correct, and that low doses actually reduce risk.

Microdosimetric Model for the Induction of Cell Killing through Medium‐Borne Signals

Microbeam, medium-transfer and low-dose experiments have demonstrated that intercellular signals can initiate many of the same biological events and processes as direct exposure to ionizing radiation. These phenomena cast doubt on cell-autonomous modes of action and the linear, no-threshold carcinogenesis paradigm. To account for the effects of intercellular signals, new approaches are needed to relate dosimetric quantities to the emission and processing of signals by irradiated and unirradiated cells. In this paper, microdosimetric principles are used to develop a stochastic model to relate absorbed dose to the emission and processing of cell death signals by unirradiated cells. Our analyses of published results of medium transfer experiments performed using HPV-G human keratinocytes suggest that the emission of death signals is a bi-exponential function of dose with a distinct plateau in the 5- to 100-mGy range. However, the emission of death signals by HPV-G cells may not become fully saturated until the absorbed dose becomes larger than 0.6 Gy. Similar saturation effects have been observed in microbeam and medium-transfer experiments with other mammalian cell lines. The model predicts that the cell-killing effect of medium-borne death signals decreases exponentially as the absorbed dose becomes small compared to the frequency-mean specific energy per radiation event.

Weight of evidence: a review of concept and methods

"Weight of evidence" (WOE) is a common term in the published scientific and policy-making literature, most often seen in the context of risk assessment (RA). Its definition, however, is unclear. A systematic review of the scientific literature was undertaken to characterize the concept. For the years 1994 through 2004, PubMed was searched for publications in which "weight of evidence" appeared in the abstract and/or title. Of the 276 papers that met these criteria, 92 were selected for review: 71 papers published in 2003 and 2004 (WOE appeared in abstract/title) and 21 from 1994 through 2002 (WOE appeared in title). WOE has three characteristic uses in this literature: (1) metaphorical, where WOE refers to a collection of studies or to an unspecified methodological approach; (2) methodological, where WOE points to established interpretative methodologies (e.g., systematic narrative review, meta-analysis, causal criteria, and/or quality criteria for toxicological studies) or where WOE means that "all" rather than some subset of the evidence is examined, or rarely, where WOE points to methods using quantitative weights for evidence; and (3) theoretical, where WOE serves as a label for a conceptual framework. Several problems are identified: the frequent lack of definition of the term "weight of evidence," multiple uses of the term and a lack of consensus about its meaning, and the many different kinds of weights, both qualitative and quantitative, which can be used in RA. A practical recommendation emerges: the WOE concept and its associated methods should be fully described when used. A research agenda should examine the advantages of quantitative versus qualitative weighting schemes, how best to improve existing methods, and how best to combine those methods (e.g., epidemiology's causal criteria with toxicology's quality criteria).

Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries

BACKGROUND

Diagnostic X-rays are the largest man-made source of radiation exposure to the general population, contributing about 14% of the total annual exposure worldwide from all sources. Although diagnostic X-rays provide great benefits, that their use involves some small risk of developing cancer is generally accepted. Our aim was to estimate the extent of this risk on the basis of the annual number of diagnostic X-rays undertaken in the UK and in 14 other developed countries.

METHODS

We combined data on the frequency of diagnostic X-ray use, estimated radiation doses from X-rays to individual body organs, and risk models, based mainly on the Japanese atomic bomb survivors, with population-based cancer incidence rates and mortality rates for all causes of death, using life table methods.

FINDINGS

Our results indicate that in the UK about 0.6% of the cumulative risk of cancer to age 75 years could be attributable to diagnostic X-rays. This percentage is equivalent to about 700 cases of cancer per year. In 13 other developed countries, estimates of the attributable risk ranged from 0.6% to 1.8%, whereas in Japan, which had the highest estimated annual exposure frequency in the world, it was more than 3%.

INTERPRETATION

We provide detailed estimates of the cancer risk from diagnostic X-rays. The calculations involved a number of assumptions and so are inevitably subject to considerable uncertainty. The possibility that we have overestimated the risks cannot be ruled out, but that we have underestimated them substantially seems unlikely.