Dose Estimation for the European Epidemiological Study on Pediatric Computed Tomography (EPI-CT)

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Comparing fetal phantoms with surrogate organs in female phantoms during CT exposure of pregnant patients

With the rising use of Computed Tomography (CT) in diagnostic radiology, there are concerns regarding radiation exposure to sensitive groups, including pregnant patients. Accurately determining the radiation dose to the fetus during CT scans is essential to balance diagnostic efficacy with patient safety. This study assessed the accuracy of using the female uterus as a surrogate for fetal radiation dose during CT imaging. The study used common CT protocols to encompass various scenarios, including primary beam, scatter, and partial exposure. The computational program NCICT was used to calculate radiation doses for an adult female and a fetus phantom. The study highlighted that using the uterus for dose estimation can result in consistent underestimations of the effective dose, particularly when the fetus lies within the primary radiation beam. These discrepancies may influence clinical decisions, affecting care strategies and perceptions of associated risks. In conclusion, while the female uterus can indicate fetal radiation dose if the fetus is outside the primary beam, it is unreliable when the fetus is within the primary beam. More reliable abdomen/pelvic organs were recommended.

Reconstruction of organ doses for patients undergoing computed tomography examinations in Canada 1992-2019

We derived the first comprehensive organ dose library for Canadian pediatric and adult patients who underwent computed tomography (CT) scans between 1992 and 2019 to support epidemiological analysis of radiation risk. We calculated organ absorbed doses for Canadian CT patients in two steps. First, we modeled Computed Tomography Dose Index (CTDI) values by patient age, scan body part, and scan year for the scan period between 1992 and 2019 using national survey data conducted in Canada and partially the United Kingdom survey data as surrogates. Second, we converted CTDI values to organ absorbed doses using a library of organ dose conversion coefficients built in an organ dose calculation program, the National Cancer Institute dosimetry system for CT. In result, we created a library of doses delivered to 33 organs and tissues by different patient ages and genders, scan body parts and scan years. In the scan period before 2000, the organs receiving the greatest dose in the head, chest and abdomen-pelvis scans were the active marrow (3.7-15.2 mGy), lungs (54.7-62.8 mGy) and colon (54.9-68.5 mGy), respectively. We observed organ doses reduced by 24% (pediatric head and torso scans, and adult head scans) and 55% (adult torso scans) after 2000. The organ dose library will be used to analyse the risk of radiation exposure from CT scans in the Canadian CT patient cohort.

Radiation-Related Thyroid Cancer

Radiation is an environmental factor that elevates the risk of developing thyroid cancer. Actual and possible scenarios of exposures to external and internal radiation are multiple and diverse. This article reviews radiation doses to the thyroid and corresponding cancer risks due to planned, existing, and emergency exposure situations, and medical, public, and occupational categories of exposures. Any exposure scenario may deliver a range of doses to the thyroid, and the risk for cancer is addressed along with modifying factors. The consequences of the Chornobyl and Fukushima nuclear power plant accidents are described, summarizing the information on thyroid cancer epidemiology, treatment, and prognosis, clinicopathological characteristics, and genetic alterations. The Chornobyl thyroid cancers have evolved in time: becoming less aggressive and driver shifting from fusions to point mutations. A comparison of thyroid cancers from the 2 areas reveals numerous differences that cumulatively suggest the low probability of the radiogenic nature of thyroid cancers in Fukushima. In view of continuing usage of different sources of radiation in various settings, the possible ways of reducing thyroid cancer risk from exposures are considered. For external exposures, reasonable measures are generally in line with the As Low As Reasonably Achievable principle, while for internal irradiation from radioactive iodine, thyroid blocking with stable iodine may be recommended in addition to other measures in case of anticipated exposures from a nuclear reactor accident. Finally, the perspectives of studies of radiation effects on the thyroid are discussed from the epidemiological, basic science, and clinical points of view.

Frequentist model averaging for analysis of dose-response in epidemiologic studies with complex exposure uncertainty

In epidemiologic studies, association estimates of an exposure with disease outcomes are often biased when the uncertainties of exposure are ignored. Consequently, corresponding confidence intervals (CIs) will not have correct coverage. This issue is particularly problematic when exposures must be reconstructed from physical measurements, for example, for environmental or occupational radiation doses that were received by a study population for which radiation doses cannot be measured directly. To incorporate complex uncertainties in reconstructed exposures, the two-dimensional Monte Carlo (2DMC) dose estimation method has been proposed and used in various dose reconstruction efforts. The 2DMC method generates multiple exposure realizations from dosimetry models that incorporate various sources of errors to reflect the uncertainty of the dose distribution as well as the uncertainties in individual doses in the exposed population. Traditional measurement-error model approaches, typically based on using mean doses in the dose-exposure analysis, do not fully account exposure uncertainties. A recently developed statistical approach that overcomes many of these limitations by analyzing multiple exposure realizations in relation to disease risk is Bayesian model averaging (BMA). The analytic advantage of the BMA is its ability to better accommodate complex exposure uncertainty in the risk estimation, but a practical. Drawback is its significant computational complexity. In this present paper, we propose a novel frequentist model averaging (FMA) approach which has all the analytical advantages of the BMA method but is much simpler to implement and computationally faster. We show in simulations that, like BMA, FMA yields 95% confidence intervals for association parameters that close to 95% coverage rate. In simulations, the FMA has shorter length of CIs than those of another frequentist approach, the corrected information matrix (CIM) method. We illustrate the similarities in performance of BMA and FMA from a study of exposures from radioactive fallout in Kazakhstan.

Risk of hematological malignancies from CT radiation exposure in children, adolescents and young adults

Over one million European children undergo computed tomography (CT) scans annually. Although moderate- to high-dose ionizing radiation exposure is an established risk factor for hematological malignancies, risks at CT examination dose levels remain uncertain. Here we followed up a multinational cohort (EPI-CT) of 948,174 individuals who underwent CT examinations before age 22 years in nine European countries. Radiation doses to the active bone marrow were estimated on the basis of body part scanned, patient characteristics, time period and inferred CT technical parameters. We found an association between cumulative dose and risk of all hematological malignancies, with an excess relative risk of 1.96 (95% confidence interval 1.10 to 3.12) per 100 mGy (790 cases). Similar estimates were obtained for lymphoid and myeloid malignancies. Results suggest that for every 10,000 children examined today (mean dose 8 mGy), 1-2 persons are expected to develop a hematological malignancy attributable to radiation exposure in the subsequent 12 years. Our results strengthen the body of evidence of increased cancer risk at low radiation doses and highlight the need for continued justification of pediatric CT examinations and optimization of doses.

Complete patient exposure during paediatric brain cancer treatment for photon and proton therapy techniques including imaging procedures

Background

In radiotherapy, especially when treating children, minimising exposure of healthy tissue can prevent the development of adverse outcomes, including second cancers. In this study we propose a validated Monte Carlo framework to evaluate the complete patient exposure during paediatric brain cancer treatment.

Materials and methods

Organ doses were calculated for treatment of a diffuse midline glioma (50.4 Gy with 1.8 Gy per fraction) on a 5-year-old anthropomorphic phantom with 3D-conformal radiotherapy, intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) and intensity modulated pencil beam scanning (PBS) proton therapy. Doses from computed tomography (CT) for planning and on-board imaging for positioning (kV-cone beam CT and X-ray imaging) accounted for the estimate of the exposure of the patient including imaging therapeutic dose. For dose calculations we used validated Monte Carlo-based tools (PRIMO, TOPAS, PENELOPE), while lifetime attributable risk (LAR) was estimated from dose-response relationships for cancer induction, proposed by Schneider et al.

Results

Out-of-field organ dose equivalent data of proton therapy are lower, with doses between 0.6 mSv (testes) and 120 mSv (thyroid), when compared to photon therapy revealing the highest out-of-field doses for IMRT ranging between 43 mSv (testes) and 575 mSv (thyroid). Dose delivered by CT ranged between 0.01 mSv (testes) and 72 mSv (scapula) while a single imaging positioning ranged between 2 μSv (testes) and 1.3 mSv (thyroid) for CBCT and 0.03 μSv (testes) and 48 μSv (scapula) for X-ray. Adding imaging dose from CT and daily CBCT to the therapeutic demonstrated an important contribution of imaging to the overall radiation burden in the course of treatment, which is subsequently used to predict the LAR, for selected organs.

Conclusion

The complete patient exposure during paediatric brain cancer treatment was estimated by combining the results from different Monte Carlo-based dosimetry tools, showing that proton therapy allows significant reduction of the out-of-field doses and secondary cancer risk in selected organs.

Associated radiation exposure from medical imaging and excess lifetime risk of developing cancer in pediatric patients with pulmonary hypertension

Pediatric patients with pulmonary hypertension (PH) receive imaging studies that use ionizing radiation (radiation) such as computed tomography (CT) and cardiac catheterization to guide clinical care. Radiation exposure is associated with increased cancer risk. It is unknown how much radiation pediatric PH patients receive. The objective of this study is to quantify radiation received from imaging and compute associated lifetime cancer risks for pediatric patients with PH. Electronic health records between 2012 and 2022 were reviewed and radiation dose data were extracted. Organ doses were estimated using Monte Carlo modeling. Cancer risks for each patient were calculated from accumulated exposures using National Cancer Institute tools. Two hundred and forty-nine patients with PH comprised the study cohort; 97% of patients had pulmonary arterial hypertension, PH due to left heart disease, or PH due to chronic lung disease. Mean age at the time of the first imaging study was 2.5 years (standard deviation [SD] = 4.9 years). Patients underwent a mean of 12 studies per patient per year, SD = 32. Most (90%) exams were done in children <5 years of age. Radiation from CT and cardiac catheterization accounted for 88% of the total radiation dose received. Cumulative mean effective dose was 19 mSv per patient (SD = 30). Radiation dose exposure resulted in a mean increased estimated lifetime cancer risk of 7.6% (90% uncertainty interval 3.0%-14.2%) in females and 2.8% (1.2%-5.3%) in males. Careful consideration for the need of radiation-based imaging studies is warranted, especially in the youngest of children.

Brain cancer after radiation exposure from CT examinations of children and young adults: results from the EPI-CT cohort study

BACKGROUND

The European EPI-CT study aims to quantify cancer risks from CT examinations of children and young adults. Here, we assess the risk of brain cancer.

METHODS

We pooled data from nine European countries for this cohort study. Eligible participants had at least one CT examination before age 22 years documented between 1977 and 2014, had no previous diagnosis of cancer or benign brain tumour, and were alive and cancer-free at least 5 years after the first CT. Participants were identified through the Radiology Information System in 276 hospitals. Participants were linked with national or regional registries of cancer and vital status, and eligible cases were patients with brain cancers according to WHO International Classification of Diseases for Oncology. Gliomas were analysed separately to all brain cancers. Organ doses were reconstructed using historical machine settings and a large sample of CT images. Excess relative risks (ERRs) of brain cancer per 100 mGy of cumulative brain dose were calculated with linear dose-response modelling. The outcome was the first reported diagnosis of brain cancer after an exclusion period of 5 years after the first electronically recorded CT examination.

FINDINGS

We identified 948 174 individuals, of whom 658 752 (69%) were eligible for our study. 368 721 (56%) of 658 752 participants were male and 290 031 (44%) were female. During a median follow-up of 5·6 years (IQR 2·4-10·1), 165 brain cancers occurred, including 121 (73%) gliomas. Mean cumulative brain dose, lagged by 5 years, was 47·4 mGy (SD 60·9) among all individuals and 76·0 mGy (100·1) among people with brain cancer. A significant linear dose-response relationship was observed for all brain cancers (ERR per 100 mGy 1·27 [95% CI 0·51-2·69]) and for gliomas separately (ERR per 100 mGy 1·11 [0·36-2·59]). Results were robust when the start of follow-up was delayed beyond 5 years and when participants with possibly previously unreported cancers were excluded.

INTERPRETATION

The observed significant dose-response relationship between CT-related radiation exposure and brain cancer in this large, multicentre study with individual dose evaluation emphasises careful justification of paediatric CTs and use of doses as low as reasonably possible.

FUNDING

EU FP7; Belgian Cancer Registry; La Ligue contre le Cancer, L'Institut National du Cancer, France; Ministry of Health, Labour and Welfare of Japan; German Federal Ministry of Education and Research; Worldwide Cancer Research; Dutch Cancer Society; Research Council of Norway; Consejo de Seguridad Nuclear, Generalitat de Catalunya, Spain; US National Cancer Institute; UK National Institute for Health Research; Public Health England.

Cancer risk following low doses of ionising radiation - Current epidemiological evidence and implications for radiological protection

Recent studies suggest that every year worldwide about a million patients might be exposed to doses of the order of 100 mGy of low-LET radiation, due to recurrent application of radioimaging procedures. This paper presents a synthesis of recent epidemiological evidence on radiation-related cancer risks from low-LET radiation doses of this magnitude. Evidence from pooled analyses and meta-analyses also involving epidemiological studies that, individually, do not find statistically significant radiation-related cancer risks is reviewed, and evidence from additional and more recent epidemiological studies of radiation exposures indicating excess cancer risks is also summarized. Cohorts discussed in the present paper include Japanese atomic bomb survivors, nuclear workers, patients exposed for medical purposes, and populations exposed environmentally to natural background radiation or radioactive contamination. Taken together, the overall evidence summarized here is based on studies including several million individuals, many of them followed-up for more than half a century. In summary, substantial evidence was found from epidemiological studies of exposed groups of humans that ionizing radiation causes cancer at acute and protracted doses above 100 mGy, and growing evidence for doses below 100 mGy. The significant radiation-related solid cancer risks observed at doses of several 100 mGy of protracted exposures (observed, for example, among nuclear workers) demonstrate that doses accumulated over many years at low dose rates do cause stochastic health effects. On this basis, it can be concluded that doses of the order of 100 mGy from recurrent application of medical imaging procedures involving ionizing radiation are of concern, from the viewpoint of radiological protection.

Radiation Dose to Pediatric Patients From Radiopharmaceuticals

Nuclear medicine provides methods and techniques in that has benefited pediatric patients and their referring physicians for over 40 years. Nuclear medicine provides qualitative and quantitative information about overall and regional function of organs, systems, and lesions in the body. This involves applications in many organ systems including the skeleton, the brain, the kidneys and the heart as well as in the diagnosis and treatment of cancer. The practice of nuclear medicine requires the administration of radiopharmaceuticals which expose the patient to very low levels of ionizing radiation. Advanced approaches in the estimation of radiation dose from the internal distribution of radiopharmaceuticals in patients of various sizes and shapes have been developed in the past 20 years. Although there is considerable uncertainty in the estimation of the risk of adverse health effects from radiation at the very low exposure levels typically associated with nuclear medicine, some considers it prudent to be more cautious when applied to children as they are generally considered to be at higher risk than adults. Standard guidelines for administered activities for nuclear medicine procedures in children have been established including the North American consensus guidelines and the Paediatric Dosage Card developed by the European Association of Nuclear Medicine. As we move into the future, these guidelines would likely be reviewed in response to changes in clinical practice, a better understanding of radiation dosimetry as applied to children as well as new clinical applications, new advancements in the field with respect to both instrumentation and image reconstruction and processing.

Comparative analysis of physical doses and biomarker changes in subjects underwent Computed Tomography, Positron Emission Tomography-Computed Tomography, and interventional procedures

Even though the medical uses of ionizing radiation are well-acknowledged globally as vital tools for the improvement of human health, they also symbolize the major man-made sources of radiation exposure to the population. Estimation of absorbed dose and biological changes after radiation-based imaging might help to better understand the effects of low dose radiation. Because of this, we measured the Entrance Surface Dose (ESD) at different anatomical locations using Lithium tetraborate doped with manganese (Li₂B₄O₇: Mn), recorded Dose Length Product (DLP) and Dose Area Product (DAP), analyzed Chromosomal Aberration (CA), Micronucleus (MN), gamma-H2AX (γ-H2AX), and p53^ser15 proteins in the blood lymphocytes of patients (n = 267) underwent Computed Tomography (CT), Positron Emission Tomography-CT (PET/CT), and interventional procedures and healthy volunteers (n = 19). The DLP and effective doses obtained from PET/CT procedures were significantly higher (p < 0.05) when compared to CT. Fluoroscopic time and DAP were significantly higher (p < 0.05) in therapeutic compared to diagnostic interventional procedures. All the anatomical locations registered a significant amount of ESD, the ESD obtained from CT and interventional procedures were significantly (p < 0.05) higher when compared to PET/CT. Fluoroscopic time did not correlate with the ESD (eye, head, thyroid, and shoulder; R² = 0.03). CA frequency after PET/CT was significantly higher (p < 0.001) when compared to CT and interventional procedures. MN frequency was significantly higher in 24-hs (p < 0.001) post-interventional procedure compared to 2-hs. The mean ± SD of mean fluorescence intensity of γ-H2AX and p53^ser15 obtained from all subjects underwent PET/CT and interventional procedures did not show a significant difference (p > 0.05) between pre- and post-procedure. However, the relative fluorescence intensity of γ-H2AX and p53^ser15 was >1 in 58.5 % and 65.8 % of subjects respectively. Large inter-individual variation and lack of correlation between physical dose and biomarkers suggest the need for robust dosimetry with a large sample size to understand the health effects of low dose radiation.