Eye dosimetry in interventional radiology and cardiology: current challenges and practical considerations

Radiation exposure during angiographic interventions in interventional radiology - risk and fate of advanced procedures

PURPOSE

Advanced angiographic procedures in interventional radiology are becoming more important and are more frequently used, especially in the treatment of several acute life-threatening diseases like stroke or aortic injury. In recent years, technical advancement has led to a broader spectrum of interventions and complex procedures with longer fluoroscopy times. This involves the risk of higher dose exposures, which, in rare cases, may cause deterministic radiation effects, e.g. erythema in patients undergoing angiographic procedures. Against this background, these procedures recently also became subject to national and international regulations regarding radiation protection. At the same time, individual risk assessment of possible stochastic radiation effects for each patient must be weighed up against the anticipated benefits of the therapy itself. Harmful effects of the administered dose are not limited to the patient but can also affect the radiologist and the medical staff. In particular, the development of cataracts in interventionalists is a rising matter of concern. Furthermore, long-term effects of repeated and prolonged x-ray exposure have long been neglected by radiologists but have come into focus in the past years.

CONCLUSIONS

With all this in mind, this review discusses different efforts to reduce radiation exposition levels for patients and medical staff by means of technical, personal as well as organizational measures.

Assessment of eye doses to staff involved in interventional cardiology procedures in Kuwait

In this study, which is the first of its kind in the gulf region, eye doses of interventional cardiologists and nurses were measured using active dosimeters for left and right eyes, in 60 percutaneous coronary interventions in three main hospitals in Kuwait. The dose given in terms of H_p(0.07) per procedure when ceiling suspended screens were used by main operators ranged from 18.5 to 30.3 µSv for the left eye and from 12.6 to 23.6 µSv for the right eye. Taking into account typical staff workload, the results show that the dose limit of 20 mSv/year to the eyes can be exceeded for interventional cardiologists in some situations, which demonstrates the need of using additional effective radiation protection tools, e.g. protective eye spectacles, in addition to the regular and proper use of ceiling suspended screens. With indications of increase in workload, the need for availability of a dedicated active dosimeter for the regular monitoring of eye doses is emphasized.

Occupational eye dose to medical staff in various interventional cardiologic procedures: is the need for lead goggles the same in all groups of radiation workers?

Considering the increased use of interventional cardiologic procedures and concern about irradiation to the eyes, it is necessary to measure eye dose in radiation workers. The assessment of eye dose using collar dose is a routine but inaccurate method. Therefore this study was designed to measure eye dose in the radiation workers of various interventional cardiologic procedures. In this study eye dose was measured for left and right eyes in three groups of radiation workers in angiography ward of Afshar hospital in various procedures using TLD. Measurements were done separately for cardiologists, nurses and radio-technologists in 100 procedures. The nurses functioned as surgical assistants and were usually close to the table. The correlation of staff dose to exposure parameters was also investigated. Eye dose in physicians were higher than other staff in all procedures. Also the left eye dose was considerably higher than right one, especially for physicians. The median equivalent dose per procedure of left eye for physicians, nurses and radio-technologists were 7.4, 3.6, 1.4 µSv (PCI) and 3.2, 3.1, 1.3 µSv (Adhoc) and 3.2, 1.7, 1.1 µSv (CA), respectively. The annual left eye equivalent dose with (without) using lead goggles were 2.4 (15.3), 1.4 (2.2), 1.0 (1.1) mSv for physicians, nurses and radio-technologists, respectively. There were also a positive correlation between eye dose and KAP for procedures without lead goggles. The lead goggles showed lower protection effects for radio-technologists than other staff. Only 30% of physicians received a dose higher than 1/3 of the ICRP annual dose limit, therefor only physician eye dose should be monitored in catheterization labs.

The new radiation protection framework since 2019 - Implementation in Germany and comparison of some aspects in seven European countries

PURPOSE

 The implementation of EU Directive 2013/59 EURATOM (EU-BSS) of 2014 led to a reorganization of radiation protection legislation in Germany in the form of a new radiation protection law Strahlenschutzgesetz (StrlSchG) of 2017 and a new radiation protection ordinance Strahlenschutzverordnung (StrlSchV) of 2018. For application of ionizing radiation in medicine these changes affect radiology, nuclear medicine and radiotherapy. A comparison between the old and the new legal system analyses changes that are relevant for diagnostic and interventional radiology. For the important new regulation of unintended exposures, a comparison is made with the implementation of Art. 63 EU-BSS in 7 European countries.

MATERIAL AND METHODS

 The provisions of the Röntgenverordnung (RöV) and the old Strahlenschutzverordnung (StrlSchV alt), which were valid until 2018, are compared with the new legislation of StrlSchG and StrlSchV for changes in radiation protection for patients, the population and occupational radiation protection of staff members. The occupational dose limit of the eye lens was reduced. The reduction by a factor of 7.5 results in new requirements for radiation protection equipment. New requirements in teleradiology are compared with the previous regulation, as well as the necessary involvement of medical physics experts (MPE) in high dose procedures, such as CT and fluoroscopic interventions. The regulation for unintended exposures of the German StrlSchV are analyzed in terms of their reporting criteria.

RESULTS

 The principles of medical radiation protection in Germany have not changed as a result of the new radiation protection legislation from 2019 onwards. However, there are a number of changes and new requirements that must be considered and implemented. Important points are e. g. new regulations on teleradiology, early detection of diseases in asymptomatic individuals and reporting of unintended exposure of patients. As all new regulations are no longer found in only one single regulation, both knowledge of the StrlSchG and the StrlSchV are necessary.

KEY POINTS

  · The EU Directive 2013/59 EURATOM (EU-BSS) was transposed into the new German radiation protection law 2018. · The basic regulations of the RöV and old StrlSchV remain unchanged. · Newly added regulations must be known and implemented in practice. · Many regulations of the EU-BSS are so vaguely formulated that they allow a wide scope for national implementation.

CITATION FORMAT

· Loose R, Wucherer M, Walz M et al. The new radiation protection framework since 2019 - Implementation in Germany and comparison of some aspects in seven European countries. Fortschr Röntgenstr 2020; 192: 1036 - 1045.

Assessment of the Annual Eye Lens Dose for Cardiologists During Interventional Procedures Using Anthropomorphic Phantoms and mEyeDose_X Tool

OBJECTIVES

In this study, eye lens dose measurements were performed using two anthropomorphic phantoms simulating the cardiologist and patient during interventional procedures.

BACKGROUND

Interventional procedures known as areas with high potential risk and the cardiologists can receive relatively high doses to their eyes.

METHODS

This study was comprised of both phantom and computer simulations. Thermoluminescent dosimeters (TLDs) and mEyeDose_X tool were used to measure and calculate eye lens doses for the cardiologist. 144 TLDs measurements were performed using cardiac protocol for three angiographic projections: anterior-posterior (AP), left anterior oblique 90° (LAO90) and left anterior oblique 45° with cranial 30° (spider) angulations. All cine and fluoroscopy modes including the projections used in this study performed with and without protection tools.

RESULTS

The annual equivalent doses with protective tools using mEyeDose_X were found to be 1.831 and 1.424 mSv/year, whereas the values using phantom were found to be 2.204 and 1.802 mSv/year for the lens of lift and right eye respectively.

CONCLUSION

The annual doses reported in this study are almost comparable to other studies performed on interventional cardiology (IC) procedures. The highest dose rate in the lens was 20.21 ± 0.015 mSv/h without protective tools in cine mode for spider projection. Cardiologists may therefore easily exceed the lens dose limit if protective tools are not used.

OCCUPATIONAL EYE LENS DOSE ESTIMATED USING WHOLE-BODY DOSEMETER IN INTERVENTIONAL CARDIOLOGY AND RADIOLOGY: A MONTE CARLO STUDY

Medical personnel performing interventional procedures in cardiology and radiology is considered to be a professional group exposed to high doses of ionizing radiation. Reduction of the eye lens dose limit made its assessment in the interventional procedures one of the most challenging topics. The objective of this work is to assess eye lens doses based on the whole-body doses using methods of computational dosimetry. Assessment included different C-arm orientations (PA, LAO and RAO), tube voltages (80 -110 kV) and efficiency of different combinations of protective equipment used in interventional procedures. Center position at the height of the thyroid gives best estimate of eye lens dose, with spreads of 11% (13%), 13% (17%) and 14% (13%) for the left (right) eye lens. The conversion factors of 1.03 (0.83), 1.28 (1.06) and 1.36 (1.06) to convert whole body to eye lens dose were derived for positions of first operator, nurse and radiographer, respectively. The eye lens dose reduction factors for different combinations of applied protective equipment are 178, 5 and 6, respectively.

Radiobiology in Cardiovascular Imaging

The introduction of ionizing radiation in medicine revolutionized the diagnosis and treatment of disease and dramatically improved and continues to improve the quality of health care. Cardiovascular imaging and medical imaging in general, however, are associated with a range of radiobiologic effects, including, in rare instances, moderate to severe skin damage resulting from cardiac fluoroscopy. For the dose range associated with diagnostic imaging (corresponding to effective doses on the order of 10 mSv [1 rem]), the possible effects are stochastic in nature and largely theoretical. The most notable of these effects, of course, is the possible increase in cancer risk. The current review addresses radiobiology relevant to cardiovascular imaging, with particular emphasis on radiation induction of cancer, including consideration of the linear nonthreshold dose-response model and of alternative models such as radiation hormesis.

AN ASSESSMENT OF THE DOSE REDUCTION OF COMMERCIALLY AVAILABLE LEAD PROTECTIVE GLASSES FOR INTERVENTIONAL RADIOLOGY STAFF

In light of the proposal from the International Commission on Radiological Protection for a lowered eye dose limit, now adopted by a European Union Council Directive, lead glasses may be required for some staff in interventional radiology to ensure that occupational exposure is as low as reasonably practicable. To investigate the lens protection offered from various models of lead glasses exposed to X-rays coming from a source to the left and below, calibrated radiochromic film was positioned in the lens area of a head phantom. When the source-to-eye angles were large, the dose reduction factors (the ratio of eye dose without protection to dose with protection) to the right lens area were much lower than to the left lens area, particularly with smaller-lensed glasses, due to gaps in protection between the face and the glasses. The results of this study reiterate the importance of employers providing eyewear based on the morphology of, and fit to, individual workers' faces.

EYE LENS EXPOSURE TO MEDICAL STAFF PERFORMING ELECTROPHYSIOLOGY PROCEDURES: DOSE ASSESSMENT AND CORRELATION TO PATIENT DOSE

The purpose of this study was to assess the patient exposure and staff eye dose levels during implantation procedures for all types of pacemaker therapy devices performed under fluoroscopic guidance and to investigate potential correlation between patients and staff dose levels. The mean eye dose during pacemaker/defibrillator implementation was 12 µSv for the first operator, 8.7 µSv for the second operator/nurse and 0.50 µSv for radiographer. Corresponding values for cardiac resynchronisation therapy procedures were 30, 26 and 2.0 µSv, respectively. Significant (p < 0.01) correlation between the eye dose and the kerma-area product was found for the first operator and radiographers, but not for other staff categories. The study revealed eye dose per procedure and eye dose normalised to patient dose indices for different staff categories and provided an input for radiation protection in electrophysiology procedures.

STUDY OF DOSES TO HIPPOCAMPUS OF INTERVENTIONAL CARDIOLOGISTS AND THEIR IMPLICATION FOR DOSIMETRIC MONITORING

Dosimetric monitoring and protection of the personnel involved into interventional procedures is one of the key issues nowadays, yet doses received by their brains were left without rigorous consideration so far. The paper is the fast track of the results of the pilot study of possible magnitude of operator's doses with particular focus on difference between doses in left and right hippocampi and their relation to effective doses of personnel using protective aprons. Monte Carlo simulation of irradiation in a typical interventional cardiology (IC) operation room shows that for standard C-arm angulations difference in doses between left and right hippocampi can be as large as 5-fold (depending on energy and projection), under certain conditions dose to left (most exposed) hippocampus can be up to two times higher than effective dose estimated by a common double dosimetry algorithm. This finding calls for closer attention to possible manifestations of health detriment associated with occupational irradiation of left hippocampus in course of IC practice.

ENERGY AND ANGULAR DEPENDENCE OF RADIOPHOTOLUMINESCENT GLASS DOSEMETERS FOR EYE LENS DOSIMETRY

Recent studies demonstrated that lens opacities can occur at lower radiation doses than previously accepted. In view of these studies, the International Commission of Radiological Protection recommended in 2011 to reduce the eye lens dose limit from 150 mSv/y to 20 mSv/y. This implies in the need of monitoring doses received by the eye lenses. In this study, small rod radiophotoluminescent glass dosemeters (GD-300 series; AGC, Japan) were characterized in terms of their energy (ISO 4037 X-rays narrow spectrum series, S-Cs and S-Co) and angular dependence (0  up to 90 degrees, with 2 ISO energies: N-60 and S-Cs). All acquisitions were performed at SCK•CEN-Belgium, using the ORAMED proposed cylindrical phantom. For selected energies (N-60, N-80, N-100, N-120 and N-250), the response of dosemeters irradiated on the ISO water slab phantom, at the Ruđer Bošković Institute-Croatia, was compared to those irradiated on the cylindrical phantom. GD-300 series showed good energy dependence, relative to S-Cs, on the cylindrical phantom. From 0 up to 45 degrees, the dosemeters showed no significant angular dependence, regardless whether they were tested when placed vertically or horizontally on the cylindrical phantom. However, at higher angles, some angular dependence was observed, mainly when the dosemeters were irradiated with low-energy photons (N-60). Results showed that GD-300 series have good properties related to Hp(3), although some improvements may be necessary.

Attenuation assessment of medical protective eyewear: the AVEN experience

The goal of this paper is to test the attenuation capability of seven models of protective eyewear used in routine clinical practice. Scattered radiation from a standard patient was simulated by using a water tank located over the treatment couch of a GE Innova 3100 x-ray angiography system. Seven protective eyewear models were tested using an anthropomorphic phantom mimicking the first operator. At each test, 4 thermoluminiscent dosimeters were placed on the phantom (respectively in front of the protective eyewear, under the eyewear, on the left earpiece and at chest level) in order to have an eyewear-independent reference. A test session without glasses was also acquired. Each model was tested with standard posterior-anterior (PA) projections and the two most common protective eyewear were tested using LAO90° and LAO45°CRA30° projections. A worst-case scenario was created to be sure of having an upper limit for the assessment of eyewear attenuation in routine clinical practice. In PA projections, the absolute attenuation value ranged between 71% and 81%, while relative attenuation between dose measured at eye lens and that measured at eyewear earpiece ranged from 67% to 85%. The slightly wider range was probably due to scatter radiation variability; anyway, differences are still included in the variable uncertainty of experimental measurements. It is worth noting that #3 eyewear model (the one without lateral protection) allows an attenuation similar to that of #5 eyewear model (with 0.5 mm lead lateral protection) in LAO90° and LAO45°CRA30° projections. Despite the experimental limitations, a description of the radiation properties of protective eyewear concerning radiation attenuation can be useful to rely on protection devices which can be used in routine clinical practice.

Eye dose assessment and management: overview

Some publications have shown that Hp(0.07) or even Hp(10) can be used as good operational quantities for X-rays in view of difficulties with Hp(3). With increasing awareness, there is tendency to use whatever dosimeter is available with correction factor to estimate eye lens dose. The best position for an eye lens dosimeter has been reported to be at the side of the head nearest to the radiation source, close to the eye. Recent studies have reported eye doses with cone beam CT (CBCT) both for patients and staff, and there are many papers reporting eye lens doses to staff in nuclear medicine. To minimise the dose to eyes, the user can take advantage of a feature of CBCT of projections acquired over an angular span of 180° plus cone angle of the X-ray tube and with tube under scan arcs.