Summary:
The frequency of Computed Tomography (CT) examinations and fluoroscopically
guided Interventional Cardiology (IC) procedures has seen significant growth
over the past decade. The extended use of these procedures raises various
radiation protection issues, as they generally result in high radiation dose to
the patient and, in the case of IC procedures, significant occupational
exposure. As a consequence, optimisation of radiation protection on CT and IC
procedures is of great importance. The European Council introduced in the
Directive 97/43/EURATOM the concept of Diagnostic Reference Levels (DRLs) as a
tool for optimization. Ever since, the establishment of DRLs of CT examinations
has been adopted in many cases at both European and national level by many
countries. Moreover, the adoption of DRLs for IC procedures has been
investigated in the literature their establishment at a national level is
required in the recent revision of the Basic Safety Standards and in the latest
Directives of the European Council. The purpose of this study is to contribute
to the optimization of patients’ and medical personnel’s exposure by
establishing national DRLs for the most common CT examinations and IC
procedures.
In order to collect a sample suitable for the establishment of DRLs, data from
91 scanners located in 38 Greek cities were collected. Sixty five of these
systems incorporate modern technologies as tube current modulation and they
provide patient exposure information (dose report) on a post study data page.
The CTDIvol and DLP for 7 common adult CT examinations were recorded and
analysed from the dose report of these systems. The remaining 26 of the systems
use constant tube current determined in the selected exam protocol and most of
them do not provide a post study data page. The dose parameters from these
systems were calculated after phantom dose measurements. The results of the
phantom dose measurements on the “older” systems were combined with the data
that were collected from the post study data page of the “modern” systems in
order to create the overall sample of the dose values. The rounded 3rd quartile
CTDIvol and DLP values were set as the DRLs for each examination.
Concerning IC, in order to set DRLs related to the procedure protocol as well
as to the X-ray systems as suggested in the literature, this study included
collection and analysis of clinical data as well as measurements related to the
performance of the X-ray systems used in IC. The performance of 30 systems was
evaluated in respect to both dosimetric and image quality parameters. Moreover,
the total fluoroscopy time and the total air Kerma – area product (KAP) of a
total of 5250 IC procedures from 26 hospitals were recorded and analyzed. This
data concerned four types of procedures, diagnostic Coronary Angiography (CA),
Percutaneous Coronary Intervention (PCI), Pacemaker Implantation (PMI) and
Radiofrequency Cardiac Ablation (RFCA). The rounded 3rd quartile of the
fluoroscopy time and the KAP values were set as the DRLs for each procedure.
Finally, KAP to effective dose conversion factors were calculated for X-ray
beam filtrations used in modern IC systems, in order to estimate the patient
effective dose during the aforementioned procedures.
The suggested national DRLs for CT examinations are generally comparable to
respective published values from similar European studies, with the exception
of sinuses CT which presents significantly higher values. This is due to the
fact that, on a significant number of systems, the examination protocol that is
used for sinuses CT is the same as the routine head CT examination. This fact,
along with the large variation of the systems’ dose values that were observed
even for scanners of the same type, indicates a need for further patient
protection optimisation without compromising the clinical outcome.
The suggested DRLs of the IC procedures are generally comparable to those
suggested by other studies. Significant variation of the mean KAP values per
centre was observed, especially for RFCA. Investigation of this variation
revealed that, for many centres, it is feasible to reduce the exposure during
this procedure by using a lower pulse rate during fluoroscopy without
compromising the clinical outcome. Concerning the phantom entrance dose
measurements, the wide range of the dose parameters that were evaluated,
represent differences not only in the systems’ dosimetric performance, but also
in the protocols used by the operating staff during the clinical work. The
latter could explain the differences in the dose measurements among systems of
the same type. This variation indicates a need for further optimisation by
either modifying the systems’ settings or by reevaluating the clinical
protocols.
In conclusion, results of the present work suggest that there is a need for
optimisation of radiation protection in the fields of Computed Tomography and
Interventional Cardiology. The adoption of the suggested national DRL by the
institutions can contribute to this goal. However, DRLs should be applied with
flexibility to allow higher doses when indicated by sound clinical judgment. In
any case, the implementation of the national DRLs can be used as a tool for the
promotion of safety culture of the stakeholders concerning radiation
protection.
Keywords:
Computed tomography, Interventional cardiology, Radiation protection, Diagnostic reference levels, Effective dose
