Estimation of risk from medical radiation exposure based on effective and organ dose: how much difference is there?

The importance of public health in radiology and radiation protection

The ionizing radiation belongs to the basic physical factors that can be measured. We forget often about its risks and the possible damage to our health. The imaging methods which use the ionizing radiation increase the diagnostics quality and they have become a certainty for many medical workers. Therefore, they are being used without rational thinking many times. With this is related to increasing the cumulative dose of patients. Next problem can be radiation safety knowledge of medical workers. The enormous increase in the use of sources ionizing radiation in medicine and rapid development, there may be a disproportionate acquisition of radiation safety knowledge of healthcare workers. At the same time, constant attention must be paid to the biological effects of radiation and realize epidemiology studies. In all the areas mentioned the public health has space. However, it is sad that presently, the radiation safety is not considered important enough in Public Health.  Based on many sources, it is safe to say that this is a major problem, because the public health itself can play an important role in radiation safety. It is important to point out, that safety and effectivity of using the source of ionizing radiation is one of the main components of Good Medical Practice.

Uses of Effective Dose: The Good, the Bad, and the Future

Effective dose (E) is a risk-adjusted dosimetric quantity developed by the International Commission on Radiological Protection. It is a key metric for practical management of the risk of stochastic health effects in a comprehensive radiation protection program. The International Commission on Radiological Protection and others have emphasized repeatedly that E is not intended to represent an actual radiation dose and should not be used as a risk-related metric for a specific person or population. The cancer risk uncertainties in the low-dose range and the underlying approximations, simplifications, and sex- and age-averaging used in generating E make it unsuitable for this purpose. However, in practice, medical imaging professionals and authors of peer-reviewed medical publications frequently and incorrectly use E as a surrogate for whole-body dose in order to calculate cancer risk estimates for specific patients or patient populations. This frequent misuse has popularized E for uses for which it was neither designed nor intended. Alternatives to E have been proposed that attempt to account for known age and sex differences in radiation sensitivity. E has also been proposed as a general indicator for communicating radiation risk to patients, if its limitations are kept in mind. Forthcoming guidance from the International Commission on Radiological Protection will likely clarify if, when, and how some form of E may be used as a rough indicator of the risk of a stochastic effect, possibly with some modifications for the substantial variations in risk known to exist with respect to age, sex, and population group.

Pediatric blunt cerebrovascular injury: the McGovern screening score

OBJECTIVE The objective of this study was to assess the incidence, diagnosis, and treatment of pediatric blunt cerebrovascular injury (BCVI) at a busy Level 1 trauma center and to develop a tool for accurately predicting pediatric BCVI and the need for diagnostic testing. METHODS This is a retrospective cohort study of a prospectively collected database of pediatric patients who had sustained blunt trauma (patient age range 0-15 years) and were treated at a Level 1 trauma center between 2005 and 2015. Digital subtraction angiography, MR angiography, or CT angiography was used to confirm BCVI. Recently, the Utah score has emerged as a screening tool specifically targeted toward evaluating BCVI risk in the pediatric population. Using logistical regression and adding mechanism of injury as a logit, the McGovern score was able to use the Utah score as a starting point to create a more sensitive screening tool to identify which pediatric trauma patients should receive angiographic imaging due to a high risk for BCVI. RESULTS A total of 12,614 patients (mean age 6.6 years) were admitted with blunt trauma and prospectively registered in the trauma database. Of these, 460 (3.6%) patients underwent angiography after blunt trauma: 295 (64.1%), 107 (23.3%), 6 (1.3%), and 52 (11.3%) patients underwent CT angiography, MR angiography, digital subtraction angiography, and a combination of imaging modalities, respectively. The BCVI incidence (n = 21; 0.17%) was lower than that in a comparable adult group (p < 0.05). The mean patient was age 10.4 years with a mean follow-up of 7.5 months. Eleven patients (52.4%) were involved in a motor vehicle collision, with a mean Glasgow Coma Scale score of 8.6. There were 8 patients (38.1%) with carotid canal fracture, 6 patients (28.6%) with petrous bone fracture, and 2 patients (9.5%) with infarction on initial presentation. Eight patients (38.1%) were managed with observation alone. The Denver, modified Memphis, Eastern Association for the Surgery of Trauma (EAST), and Utah scores, which are the currently used screening tools for BCVI, misclassified 6 (28.6%), 6 (28.6%), 7 (33.3%), and 10 (47.6%) patients with BCVI, respectively, as "low risk" and not in need of subsequent angiographic imaging. By incorporating the mechanism of injury into the score, the McGovern score only misclassified 4 (19.0%) children, all of whom were managed conservatively with no treatment or aspirin. CONCLUSIONS With a low incidence of pediatric BCVI and a nonsurgical treatment paradigm, a more conservative approach than the Biffl scale should be adopted. The Denver, modified Memphis, EAST, and Utah scores did not accurately predict BCVI in our equally large cohort. The McGovern score is the first BCVI screening tool to incorporate the mechanism of injury into its screening criteria, thereby potentially allowing physicians to minimize unnecessary radiation and determine which high-risk patients are truly in need of angiographic imaging.

NEED FOR INDIVIDUAL CANCER RISK ESTIMATES IN X-RAY AND NUCLEAR MEDICINE IMAGING

To facilitate the justification of an X-ray or nuclear medicine investigation and for informing patients, it is desirable that the individual patient's radiation dose and potential cancer risk can be prospectively assessed and documented. The current dose-reporting is based on effective dose, which ignores body size and does not reflect the strong dependence of risk on the age at exposure. Risk estimations should better be done through individual organ dose assessments, which need careful exposure characterisation as well as anatomical description of the individual patient. In nuclear medicine, reference biokinetic models should also be replaced with models describing individual physiological states and biokinetics. There is a need to adjust population-based cancer risk estimates to the possible risk of leukaemia and solid tumours for the individual depending on age and gender. The article summarises reasons for individual cancer risk estimates and gives examples of methods and results of such estimates.

Estimating the lifetime risk of cancer associated with multiple CT scans

Multiple CT scans are often done on the same patient resulting in an increased risk of cancer. Prior publications have estimated risks on a population basis and often using an effective dose. Simply adding up the risks from single scans does not correctly account for the survival function. A methodology for estimating personal radiation risks attributed to multiple CT imaging using organ doses is presented in this article. The estimated magnitude of the attributable risk fraction for the possible development of radiation-induced cancer indicates the necessity for strong clinical justification when ordering multiple CT scans.

Current knowledge on tumour induction by computed tomography should be carefully used

Risks associated to ionising radiation from medical imaging techniques have focused the attention of the medical society and general population. This risk is aimed to determine the probability that a tumour is induced as a result of a computed tomography (CT) examination since it makes nowadays the biggest contribution to the collective dose. Several models of cancer induction have been reported in the literature, with diametrically different implications. This article reviews those models, focusing on the ones used by the scientific community to estimate CT detriments. Current estimates of the probability that a CT examination induces cancer are reported, highlighting its low magnitude (near the background level) and large sources of uncertainty. From this objective review, it is concluded that epidemiological data with more accurate dosimetric estimates are needed. Prediction of the number of tumours that will be induced in population exposed to ionising radiation should be avoided or, if given, it should be accompanied by a realistic evaluation of its uncertainty and of the advantages of CTs. Otherwise they may have a negative impact in both the medical community and the patients. Reducing doses even more is not justified if that compromises clinical image quality in a necessary investigation. Key Points • Predictions of radiation-induced cancer should be discussed alongside benefits of imaging. • Estimates of induced cancers have noticeable uncertainties that should always be highlighted. • There is controversy about the acceptance of the linear no-threshold model. • Estimated extra risks of cancer are close to the background level. • Patients should not be alarmed by potential cancer induction by CT examinations.