Introduction

More than 16.5 million adults in the United States have coronary heart disease,1 which is accountable for approximately one-third of deaths in adults older than 35 years.2 Percutaneous cardiac catheterization including coronary angiography and percutaneous coronary intervention (PCI) remains an important diagnostic and therapeutic modality for patients with coronary heart disease.3 In Australia, from 2013 to 2014, 44% of patients hospitalized for coronary heart disease underwent coronary angiography, and 22% received PCI.4 The evolution of techniques and widespread applicability of coronary angiography and PCI have improved the quality of life for patients and reduced mortality rates due to coronary artery disease.3

First performed in 1929,5 cardiac catheterization is a combination of angiographic imaging and investigative hemodynamic procedures.3 Although cardiac catheterization is widely performed globally, one major disadvantage of the angiographic imaging technique is the exposure to ionizing radiation.6 When compared with other medical radiological exposures, the radiation dose delivered during fluoroscopically guided cardiac catheterization remains the highest.6 Radiation doses used during diagnostic cardiac catheterization have been reported to range from 7 millisievert (mSv) to 17 mSv for PCI7; however, doses of up to 50 mSv are necessary in some patients.8 The proceduralist is also exposed to radiation, predominantly through deflected scatter from the patient. Consequently, cardiac catheterization proceduralists have been known to accrue between 50 mSv to 200 mSv of radiation during their career.9

The radiation dose that the proceduralist receives has been reported to cause deterministic and stochastic health effects. Deterministic effects are dose related and can include skin damage and cataract formation.10 The formation of cataracts and lens opacities11 are the most common adverse effects experienced by proceduralists because of their closeness to the x-ray beam and to scattered radiation.7,9 Other adverse deterministic effects that have been reported include impaired development of an embryo or fetus, impaired reproductive function, immunodeficiency10,12 and oligospermia.7 A study that assessed the health of 466 health professionals frequently exposed to fluoroscopically guided cardiovascular procedures for a median of 10 years found a statistically significant increase in the incidence of skin lesions, cataracts and cardiovascular disease when compared with unexposed health professionals.9

Stochastic effects are characterized by delayed effects from frequent low levels of radiation exposure that evolve randomly and unpredictably.10 The biggest concern about these effects is that they include damage and mutation to cellular molecules, which can result in malignancies.10,13 Although stochastic effects are more likely to occur in those who receive cumulative doses of radiation, they can also occur at very low, non-cumulative radiation doses.12 Occupational radiation exposure has been estimated to have an associated lifetime cancer risk of one in 100,9,13,14 whereas other studies report risks of one in 500,000 to one in 1,000,000.14 However, there are no reports of a more precise estimate of risk per unit dose of radiation15 as radiation-induced malignancy presents clinically the same as spontaneously-occuring malignancy.13

The primary source of radiation exposure to proceduralists working in cardiac catheterization laboratories is from scattered radiation from the patient.6 Scattered radiation to the proceduralist is generally related to the total radiation dose emitted from the x-ray tube. However, certain practices alter the relationship between total dose and scatter dose, and include C-arm angulation and usage of personal protective devices. For this reason, increasing efforts have been made to reduce the radiation dose received by health professionals working in these specialties.

The International Basic Safety Standards for Protection Against Ionizing Radiation and the Safety of Radiation Sources have set minimum standards for staff training, qualification and knowledge to minimize operating errors, unnecessary exposures16 and the risk of stochastic effects.13 Moreover, guidelines have been developed that recommend the maximum radiation dose limit for proceduralists using fluoroscopy.17,18 In addition to these guidelines, the safety principle "As Low As Reasonably Achievable" (ALARA) for optimization of protection is recommended by the International Commission on Radiological Protection (ICRP).19,20

Numerous studies have investigated the effect of personal protective equipment including gloves,21 eyewear,22-24 caps,25,26 thyroid collars, aprons, vests and skirts27 on minimization of radiation dose among proceduralists in the cardiac catheterization laboratory.18 These garments are traditionally made of all-lead material; however, technological advances have resulted in the use of composite lead, which is significantly lighter.18,27 In a randomized controlled trial (RCT) undertaken on 210 patients undergoing elective coronary angiography, the radiation dose received by the proceduralist decreased from 20.9 +/- 13.8 mSv to 9.0 +/- 5.4 mSv (P = 0.0001) in those who used pelvic composite lead shielding.28

The use of protective shields is another strategy implemented to reduce scattered radiation and act as a barrier between the source of radiation and the proceduralist, thus minimizing the radiation dose.18 Shielding includes protective screens suspended from the ceiling,21 architectural (wall bound) protections and mounted shields that can be fixed to equipment or tables.18 However, there is controversy in the literature relating to the use of protective shields. One study29 conducted over 813 coronary angiographies found that although a lead screen limited scattered radiation to the lens of the eyes, it was largely ineffective in stopping scattered radiation to the extremities. In an RCT30 undertaken on 106 patients, the radiation dose received by the proceduralist significantly decreased among those who undertook coronary procedures on patients using a transradial radiation protection board.

Other strategies implemented to reduce occupational exposure include minimizing fluoroscopy imaging time and the number of images required, low frame rate fluoroscopy,31 use of real-time radiation monitoring,18,32,33 use of tight collimation and maximizing the distance from the x-ray beam, where possible.18,32 An RCT34 undertaken on 363 patients undergoing transradial diagnostic angiography demonstrated that there was a significant reduction in the radiation dose received by the proceduralist (30% relative reduction [RR], P < 0.0001) among patients who received fluoroscopy at 7.5 frames per second (FPS) versus 15 FPS.

Rates of cardiac catheterization are increasing exponentially, resulting in an increase in exposure to radiation among proceduralists performing cardiac catheterization. Therefore, it is important to identify the best available strategies to reduce exposure and prevent long-term adverse effects of radiation exposure.

A preliminary search was conducted in Cochrane Library, PROSPERO, CINAHL, Embase and MEDLINE to identify quantitative systematic reviews on the effect of radiation minimization strategies on radiation exposure received by cardiac proceduralists. However, the search did not find any reviews on this topic. Therefore, the aim of the systematic review is to synthesize the best available evidence from all clinical trials investigating the effect of various radiation protection strategies on radiation exposure received by cardiac proceduralists.

Inclusion criteria

Participants

The review will consider trials that include proceduralists performing cardiac catheterization procedures in adult patients 18 years and older. Trials that report on radiation dose on other health professionals in the cardiac catheterization laboratory will be excluded.

Intervention

This review will consider trials that evaluate protection strategies to reduce radiation including, but not limited to, the following:

* Personal protective equipment including thyroid collar, lead eyewear, lead aprons, lead cap and lead gloves.

* Protective shielding and drapes including table shielding, pelvic radiation shield, transradial radiation protection board and radiation protection booth.

* Procedural variables including low rate fluoroscopy at 7.5 FPS, fluoroscopy record, collimation, source to image receptor distance, image magnification, C-arm angulation, prolonging interval time between coronary angiography and PCI and staged PCI.

* System improvements including devices for injection of contrast medium, noise-reduction technology, system age, dose-tracking system, robotic coronary angiography, real-time radiation monitoring and real-time radiation maps.

* Physician education and training relating to correctly performing cardiac catheterization procedures to reduce radiation exposure dose.

All trials, irrespective of the duration of the procedure, intensity and radiation exposure, will be eligible for inclusion in this review.

Comparator

The comparator will include standard protective strategies as defined by the individual operating facility for reducing radiation dose.

Outcomes

The primary outcome for this review is the radiation dose, including scatter dose, received by proceduralists during cardiac catheterization procedures. Only trials using objective outcome measures, including but not limited to electronic personal dosimeters, of radiation dose will be included. Trials investigating only the deterministic and stochastic effects of radiation exposure, such as cataracts and malignancies, will not be included.

Types of studies

This review will consider experimental study designs including RCTs. In the absence of RCTs, non-randomized clinical trials will be included. Studies published in the English language only will be included. Studies published as far back as possible will be included.

Methods

Search strategy

The search strategy will aim to find published and unpublished studies. An initial limited search of MEDLINE via Ovid and CINAHL via EBSCOhost has been undertaken followed by analysis of the text words contained in the title and abstract, and of the index terms used to describe the article. This informed the development of a search strategy, which will be tailored for each information source. A full search strategy for MEDLINE via Ovid (up to May 2018) is detailed in Appendix I. The reference list of all studies selected for critical appraisal will be screened for additional studies.

Information sources

The databases to be searched include: MEDLINE, Cochrane Central Register of Controlled Trials, CINAHL and Embase. The trial registers to be searched include: ClinicalTrials.gov and Australian New Zealand Clinical Trials Registry. The search for unpublished studies will include: WorldCat, ProQuest Dissertations and Theses and MedNar. The ProQuest databases that will be used are Nursing and Allied Health Source Database and Health and Medical Collection (Hospital).

Study selection

Following the search, all identified citations will be collated and uploaded into Endnote vX8 (Clarivate Analytics, PA, USA) and duplicates removed. Titles and abstracts will then be screened by two independent reviewers for assessment against the inclusion criteria for the review. Studies that could potentially meet the inclusion criteria will be retrieved in full and their details imported into the Joanna Briggs Institute System for the Unified Management, Assessment and Review of Information (JBI SUMARI; Joanna Briggs Institute, Adelaide, Australia). The full text of selected studies will be retrieved and assessed in detail against the inclusion criteria. Full-text studies that do not meet the inclusion criteria will be excluded, and reasons for exclusion will be provided in an appendix in the final systematic review report. The results of the search will be reported in full in the final report and presented in a PRISMA flow diagram.35 Any disagreements that arise between the reviewers will be resolved through discussion or with a third reviewer.

Assessment of methodological quality

Selected studies will be critically appraised by two independent reviewers at the study level for methodological quality in the review using the checklist for RCTs from JBI.36 For non-randomized trials, the checklist for quasi-experimental studies from JBI will be used.36 Any disagreements that arise will be resolved through discussion or with a third reviewer. All studies, regardless of their methodological quality, will undergo data extraction and synthesis (where possible).

Data extraction

Data will be extracted from the papers included in the review using the standardized data extraction tool available in JBI SUMARI by two independent reviewers.36 The data extracted will include specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives. Any disagreements that arise between the reviewers will be resolved through discussion or with a third reviewer. Authors of papers will be contacted to request missing or additional data where required.

Data synthesis

We anticipate that the radiation doses in the individual trials will be measured using various units of radiation measurement. Hence, the data will be transformed to a single consistent metric of equivalent dose of radiation, or the mean absorbed dose over the biological effect, measured in the unit called the sievert (Sv), as defined by the Australian Radiation Protection and Nuclear Safety Agency37 and the International Atomic Energy Agency.38 The data will, where possible, be pooled in statistical meta-analysis using JBI SUMARI. Effect sizes will be expressed as weighted or standardized mean differences for continuous data, and their 95% confidence intervals will be calculated. Heterogeneity will be assessed statistically using the standard chi-squared and I² tests. The choice of model (random or fixed effects) and method for meta-analysis will be based on the guidance by Tufanaru et al.39

Subgroup analyses will be conducted to investigate the effectiveness of various radiation protection strategies for transradial and transfemoral percutaneous coronary procedures. Given that the radiation dose required for PCI is higher than coronary angiography,40 a subgroup analysis will also be undertaken to investigate the effectiveness of various radiation protection strategies for these two procedures. Where statistical pooling is not possible, the findings will be presented in narrative form including tables and figures to aid in the data presentation, where appropriate. A funnel plot will be generated to assess publication bias if there are 10 or more studies included in a meta-analysis. Statistical tests for funnel plot asymmetry (Egger test, Begg test, Harbord test) will be performed, where appropriate.41

Assessing certainty in the findings

A Summary of Findings will be created using GRADEpro GDT software (McMaster University, ON, Canada). The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach for grading the quality of evidence will be followed. The Summary of Findings will present the following information where appropriate: absolute risks for treatment and control, estimates of relative risk and a ranking of the quality of the evidence based on study limitations (risk of bias), indirectness, inconsistency, imprecision and publication bias.

The following outcome will be included in the Summary of Findings: radiation dose in proceduralists.

Appendix I: Search strategy for MEDLINE via Ovid

References