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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 4, July/August 2017
230
AFRICA
camera, MPI provides information that can be used to both
diagnose coronary artery disease and stratify risk, and thus guide
patient management.
1-3
While the benefits of MPI are apparent, there are concerns
regarding potential harmful effects from radiation exposure as
a result of undergoing this procedure.
4
Therefore, organisations
promoting radiation safety, such as the International Commission
on Radiological Protection (ICRP), advocate practice to use
radiation only when justified and to limit radiation to levels
that are ‘as low as reasonably achievable’ (ALARA) without
compromising on diagnostic information.
5
While judicious application of imaging technology that
employs ionising radiation is the best approach, numerous
techniques or ‘best practices’ exist to assist practitioners in
limiting the dose when its use is warranted.
6-9
A recent study
conducted by the International Atomic Energy Agency (IAEA)
revealed significant variation in both the uptake of evidence-
based best practices to reduce patient radiation exposure and
patient radiation effective dose from MPI among nuclear
cardiology laboratories worldwide.
9
Beyond this study, little is known about nuclear cardiology
practice with regard to radiation exposure around the world,
especially among laboratories in Africa. The purpose of this
study was to characterise the MPI practice and patient dose
among African nuclear cardiology laboratories participating in
the IAEA Nuclear Cardiology Protocols Study (INCAPS), and
examine it relative to practice among laboratories worldwide.
Methods
This study used patient and laboratory data collected as part
of the worldwide INCAPS survey. INCAPS was initiated by an
expert committee of physicians and medical physicists convened
by the IAEA to characterise radiation doses and examine
best-practice use to minimise dose in nuclear cardiology clinics
around the world.
INCAPS used a cross-sectional design whereby participating
laboratories provided demographics, clinical characteristics and
MPI study parameters for a consecutive sample of patients
over a one-week period of the laboratory’s choice between 18
March and 22 April 2013. Nuclear cardiology laboratories
were recruited through membership lists provided by a number
of national and international cardiology or nuclear medicine
societies. A designated local investigator prospectively acquired
data using a standardised data-collection tool that was issued
by the coordinating centre. This included information on the
patient’s age, gender and weight, and MPI study parameters,
such as injected radiopharmaceutical, administered activity,
camera type, imaging position and protocol, and camera-based
dose-mediating hardware or software. Full details regarding
study design are presented elsewhere.
9
The study was reviewed, approved and conducted in compliance
with the Columbia University institutional review board, which
deemed it exempt from the requirements of US federal regulations
for the protection of human subjects (45 CFR 46) because no
individually identifiable health information was collected.
Radiation dose was calculated for each patient using the
effective dose (ED), as per the dose coefficients provided by
the ICRP.
10
ED is a whole-body measure that reflects both
estimated individual organ doses and their relative sensitivity to
carcinogenic effects from radiation. Radiation dose from studies
using rubidium-82 was calculated using Senthamizhchelvan’s
conversion coefficients.
11
All radiation doses are presented in
units of millisieverts (mSv). Mean and median EDwas calculated
at the laboratory and regional (Africa vs rest of the world) level.
Using current clinical practice guidelines, the expert
committee convened by the IAEA identified eight ‘best practices’
for optimising radiation dose from MPI studies
a priori
. A
laboratory’s adherence to each of these practices was evaluated
from the acquired data. Details regarding how the best practices
are defined and adherence scored were reported previously by
Einstein
et al
.
9
and are summarised in Table 1.
Briefly, these best practices centred around the practice
of avoiding administering higher-than-needed doses of
radiopharmaceuticals, using a strategy of stress-only imaging
where possible, avoiding dosing leading to ‘shine through’
artifact, and the use of camera-based dose-reduction software
or hardware technology (e.g. resolution recovery software or
two-position supine and prone imaging), which can reduce
radiation dose. Stress-only imaging refers to a protocol whereby
rest imaging is only acquired in the event that stress images,
which are performed first, reveal abnormalities. The use of
this protocol has been shown to reduce radiation exposure,
as a significant proportion of the population will not require
the subsequent rest imaging.
12
When performing single-day,
two-injection technetium studies, there is a possibility of residual
activity from the first injection interfering with the interpretation
of images from the second injection. This shine-through artifact
can be avoided by ensuring the administered activity in the second
injection is more than three times that of the first injection.
A composite quality index (QI) was enumerated for each
laboratory, based on the number of specified best practices
followed during the observation period. The expert committee
established a median laboratory ED of
≤
9 mSv, as specified in
professional society recommendations,
13
and a QI score of
≥
6 as
benchmarks for desirable laboratory performance.
Statistical analysis
The primary comparison examined patient ED and laboratory
best-practice adherence differences between Africa and the rest
of the world. As a second focus, ED was compared between
laboratories within Africa. For continuous variables, normality
was tested using the Kolmogorov–Smirnov test for patient-level
comparisons, given the large sample size of 7 911, and using the
Shapiro–Wilk test for laboratory-level comparisons. Continuous
variables were compared in terms of means using the Student’s
t
-test or analysis of variance for normally distributed data and
compared in terms of medians using the Kruskal–Wallis test for
non-normally distributed data. The chi-squared test was used to
compare categorical variables. All analyses were performed using
Stata/SE 13.1 (StataCorp, College Station, TX) and a
p
-value
<
0.05 was considered statistically significant.
Results
Of the 30 laboratories performing MPI in Africa, identified in
the IAEA Nuclear Medicine database, data collection yielded
information on 348 consecutive MPI studies from 12 laboratories
in Algeria, Egypt, Kenya, Senegal, South Africa and Tunisia. It