The terms “notifications” and “alerts” for some medical exposures are being used by standardisation organisations, by the Food and Drug Administration (FDA), and by several interventional radiology societies to provide information of certain radiation quantities in relation to patient doses [1,2,3,4,5].
A United States (US) technical standard (XR 25) published by the National Electrical Manufacturers Association (NEMA) in 2010 [1] has been used by the American Association of Physicists in Medicine (AAPM) to produce a set of “Recommendations Regarding Notification and Alert Values for CT Scanners” [3]. Also, the International Electrotechnical Commission (IEC) has included these terms in some of its documents [4] and it is expected that the definitions will be improved in the future. Dose notification and alert values for CT are based on computed tomography dose index (CTDIvol), which are related to a constant phantom size, independent of the real patient size.
The North American Society of Interventional Radiology (SIR) and the Cardiovascular and Interventional Radiology Society of Europe (CIRSE) published a set of dose notifications for fluoroscopy-guided interventional procedures (FGIP) [5].
Notifications and alerts may also be useful for optimisation to avoid “unintended and accidental exposures”. This is required by the European Basic Safety Standards directive [6]. A specific section on alarms for these exposures is also included in this review.
Computed tomography (CT) scanners in compliance with the NEMA standard can be configured to inform users when scan settings would yield values of CTDIvol and dose length product (DLP) that would exceed pre-assigned values. Compliant scanners allow users to confirm or correct settings that might otherwise lead to unnecessarily high exposures, before proceeding with scanning. Manufacturers may include pre-assigned values in their default protocols, but all values are user-configurable [3].
The primary purpose of notification and alert values for CT, as intended by the FDA in their request to manufacturers, is to prevent relevant errors at the time of the patient scan. It is also important to develop criteria regarding the level of detail that is required to be included in the event registry, as well as defining which member(s) of a practice are authorised to approve to proceed with a scan where CTDIvol and DLP would exceed the alert level [7].
The main interest in using these values for high-dose procedures (CT and FGIP) is the avoidance of radiation skin injuries, but alerts in X-ray systems may be considered before procedures (as in CT), during procedures (as in some interventional radiology systems), and after procedures, when the patient dose descriptor results are known and processed. High patient dose values may also involve high occupational doses and this should be considered in optimisation.
There are few reported experiences on the practical use of these notifications and alerts in CT and their impact on the workflow of radiology departments and on the optimisation of radiation protection of patients. Howard et al [7] reported a 1.2% level for triggering a notification for CT examinations (large patient size and bolus tracking). However, authors note that the low percentage of alerts found was due to three factors: the review process of the protocols, an optimised practice in large patients, and the use of only new scanners.
There are more publications and international recommendations that deal with radiation skin injuries in FGIP [8, 9].
Alerts and trigger levels are useful tools to optimise imaging procedures, reducing the probability of stochastic effects and avoiding tissue reactions (deterministic effects).
In diagnostic and interventional radiology, the two terms (notifications and alerts) and sometimes other terms such as “threshold value” or “significant dose events” are used to inform about a high (or potentially high) skin dose for the patient or for unintended exposures. Sometimes, other patient organs with a risk of radiation injury, such as the lenses of the eyes and the cerebrovascular or cardiovascular systems, may be also considered [10,11,12,13].
This review summarises the different uses of notifications and alerts to help in optimisation for CT and for fluoroscopy-guided interventional procedures as well as in the analysis of unintended and accidental medical exposures. The paper includes cautions in setting the alert values and discusses the benefits of using patient dose management systems for the alerts, their registry and follow-up, and the differences between alerts for individual procedures and diagnostic reference levels (DRLs).