The three fundamental principles of radiological protection are justification, optimisation, and dose limits. For optimisation, the International Commission on Radiological Protection (ICRP) recommends the use of diagnostic reference levels (DRLs) [1]. The DRLs are considered vital elements in dose monitoring and are used as enhancers of optimisation and good radiological practices. They represent the 75th percentile (P75) of a dose distribution in a specific radiological procedure [2].
The DRLs are not established as radiation limits, nor are they intended for individual patients; instead, they are extremely important values for comparing local practices with international recommendations or other centers. If the obtained DRLs values exceeds these benchmarks, an investigation should be conducted, and corrective measures should be implemented to optimize radiation dose [1, 3]. The ICRP acknowledges that establishing DRLs for interventional radiology procedures is more complex due to the anatomical and clinical variability of patients and the complexity of the pathologies undergoing treatment [3].
In INR, minimally invasive procedures guided by fluoroscopy are a highly effective treatment option for various neurovascular conditions. However, due to the complexity of pathologies, some procedures may involve high doses of exposure to ionising radiation for both patients and healthcare professionals, increasing the likelihood of deterministic and stochastic effects [4]. Monitoring practices, awareness of radiation effects, advancements in fluoroscopy equipment, and image parameters are fundamental premises to consider in INR procedures aimed at establishing DRLs [4]. However, the exponential increase in endovascular techniques using ionising radiation has not been accompanied by a corresponding increase in awareness and knowledge among healthcare professionals involved [5]. In most cases, there is a significant underestimation of radiation doses for the most common procedures [5].
Radiation protection 175 advocates for comprehensive training in radiological protection to ensure the safety and efficacy of medical procedures involving radiation. This guideline highlights that all team members involved in such procedures must be well-versed in the principles of radiation safety to minimize exposure to both patients and staff [6]. Similarly, the European project Medical Radiation Protection Education and Training (MEDRAPET), which is an European initiative, aims to enhance the quality and consistency of radiological protection education and training across Europe. The project stresses that proper training in radiological protection is essential for maintaining high standards of patient care and occupational safety in medical settings where radiation is used [6].
In summary, education in radiological protection should be considered an essential part of the training process for teams involved in fluoroscopy-guided procedures [5]. It is crucial to implement the principle of optimisation as a promoter of healthcare quality. Therefore, it is important to be familiar with and understand the most relevant dose descriptors, as well as the DRLs calculated in various studies [5].
The air kerma area product (PKA), formerly known as dose area product (DAP) or kerma area product (KAP), represents the dose measured by an ionization chamber positioned at the exit of the primary X-ray beam [5, 7, 8]. The air kerma, expressed in Grays (Gy), is multiplied by the cross-sectional area of the primary X-ray beam in cm2. The result of this product is expressed in Gy·cm2 [5]. Recent equipment internally calculates the value of PKA using exposure factors such as tube voltage (kVp), tube current time product (mAs), beam position in relation to the patient, and field of view (FOV), in addition to the collimation used [5].
The air kerma at the patient entrance reference point (Ka, r) is calculated as a point located between the X-ray tube and the detector, 15 cm below the isocenter in the direction of the tube’s focal spot, known as the patient entrance reference point. It does not take into account scattered radiation and is expressed in Gy [5]. It is important to emphasize that Ka, r does not correspond to the skin dose, does not provide a mapping of the skin dose, nor does it serve as a reference for the peak skin dose (PSD), although it can be used for its estimation [5].
The standard reference for mapping the PSD has been the use of radiochromic films [9]. Recently, new software solutions from different manufacturers have been tested to provide mapping of skin dose, showing promising results compared to radiochromic films [5, 9].
In 2007, the ICRP recommended extending the concept of reference levels to interventional radiology as a means of monitoring patient doses, aiming to prevent unnecessary risks associated with radiation exposure [10, 11]. The determination of DRLs can be conducted through surveys or measurements of radiation doses in hospitals, regions, or a country [11].
In the European Union, the establishment and use of DRLs in each member state have been mandatory since 1997. This requirement was reinforced by the standards set in the new European Directive 2013/59/Euratom, which establishes basic safety standards for protection against the dangers arising from exposure to ionising radiation, published in 2014 [5].
According to ICRP 135, DRLs values should be calculated based on the P75 of the frequency distribution of the analyzed values, including PKA, Ka, r [5, 11, 12], and fluoroscopy time (FT) [13].
DRLs pose a challenge for INR due to the complexity and variability of procedures [3], clinical indications, and the patient’s weight and height, while not neglecting the crucial importance of image quality. They should be considered dynamic, flexible, and serve as a reference for best practices. However, it is necessary to take into account the patients’ body mass index (BMI), clinical conditions, type of equipment, and the experience of the operators [5]. There are authors who overlook the BMI for head and neck procedures [14].
Cerebrovascular disease has a high incidence rate and is one of the leading causes of death and comorbidity, particularly in cases of stroke [15]. In INR, various deterministic complications arise from the effects of ionising radiation, such as cutaneous erythema, which occurs with a dose limit of 2 Gy, while 7 Gy can cause permanent hair loss [16]. The formation of cataracts is a significant risk, as the patient’s eyes are exposed to radiation throughout the procedure [16]. The dose to the lens of the INR team is also a concern. The ICRP recommends reducing the threshold dose for cataract induction from 2 to 0.5 Gy. As a result, the dose limit for ocular exposure among the team has been reduced from 150 to 20 mSv per year (averaged over a 5-year period) [16].
The main objectives of this systematic review are to analyze the most important dose descriptors in fluoroscopy-guided procedures and to compare the values of DRLs in various existing INR procedures found in recent literature.
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