1. Limiting the risks of radiation
exposure in diagnostic imaging
Preston Ray,a
Thinh Vu, MD,b
Minerva Romero, MD, MPH,a
and Nancy D. Perrier, MD, FACS,a
Houston, TX
From the Departments of Surgical Oncologya
and Neuroradiology,b
The University of Texas M.D. Anderson
Cancer Center, Houston, TX
THIS REPORT BY THE JOHNS HOPKINS’ GROUP discusses
the development that multiphase computed to-
mography (CT) as becoming a favored imaging
modality for complex parathyroid localization.1
The article cites delineation of hyperfunctioning
parathyroid tissue from other structures by relating
density on unenhanced CT to the rapidity of
enhancement following contrast injection. The
‘‘fourth dimension’’ (4D) of perfusion over time
has excellent predictive power for localization.
The additional ‘‘washout phase’’ has been cited
to increase reader confidence. In this article, Nour-
eldine et al recommend eliminating $1 aspects of
serial scans to decrease the effective radiation
dosing. We support decreasing radiation exposure
to the patient using an informative and respon-
sible risk–benefit strategy.
To understand the risk, a basic knowledge of
radiation dosage terms is needed. Effective dose is a
probabilistic estimate of the total amount of radia-
tion absorbed at different doses by the tissues
exposed (Table I).2
Measured in Sieverts (Sv)
and used mainly to evaluate radiation risks in pa-
tients, effective doses are difficult to calculate
because they depend largely on estimating ab-
sorbed doses from CT.2
Although estimating effec-
tive dose has many limitations, such as not being
specific to patient size or gender, it is commonly
used for medical imaging examinations involving
radiation. Exposure is the ionization produced in
a specific volume of air as radiation waves strip
electrons from air molecules.2
Absorbed dose is
the amount of energy absorbed per unit of mass
in a particular tissue, measured in grays (Gy).2
Although the radiation used in diagnostic im-
aging accounts for <50% of all radiation exposure
in the United States,3
a 2004 study suggested that
medical exposure might be responsible for
approximately 1% of the cancer in the United
States.4
However, it is difficult to isolate radiation-
induced cancers (1/1,000 per 10-mSv effective
dose) that are superimposed on the normal back-
ground risk for other cancers (approximately
40% of the population will be diagnosed as having
cancer at some point in their lives).5
Table II lists
the approximate effective doses for various forms
of radiation exposure. Some form of radiation,
including radioactive materials and ultraviolet
rays, is believed to play a role in #10% of all cases
of invasive cancer.6
A 2009 study brought medical radiation expo-
sure risks into the spotlight. In 2007, an estimated
72 million CTs were performed in the United
States---nearly 200,000 CT per day, or >2 scans per
second.4
Essentially, the issue of radiation expo-
sure narrows down to 2 overarching questions:
How can risk be minimized, and how much is
too much exposure? With awareness, clinicians
can make informed decisions about this risk–
benefit ratio pertaining to diagnostic imaging
involving radiation.7
Avoiding low-quality imaging
reduces the need for repetitive scanning. Accord-
ing to the principle of ALARA (as low as reason-
ably achievable), the absorbed dose should be
the lowest needed for a good image.8
The Image
Gently and Image Wisely campaigns represent
many professional organizations working to reduce
the use of medical radiation in children and
adults, respectively. Predicting radiation risk for in-
dividual patients is difficult because the risk de-
pends on the patient’s size, gender, age, and
targeted organs. The risk is greater for young pa-
tients than for older patients because young pa-
tients have longer to live with the absorbed dose
and their tissues are more sensitive to radiation
10.1016/j.surg.2014.08.002
Accepted for publication August 22, 2014.
Reprint requests: Nancy D. Perrier, MD, FACS, The University of
Texas M.D. Anderson Cancer Center, 1400 Pressler Dr., Unit
1484, Houston, TX 77030. E-mail: NPerrier@mdanderson.org.
Surgery 2014;156:1297-9.
0039-6060/$ - see front matter
Ó 2014 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.surg.2014.08.085
SURGERY 1297

2. damage. In addition, the sensitivity of the targeted
organ has a significant impact on the effective
dose, depending on the concentration of mito-
chondria and the frequency of mitosis. The risk
can be greater for females than for males if breast
tissue is exposed to radiation. Because of these
variations in risk, specific protocols cannot be
developed, and treating clinicians must treat each
patient according to the patient’s needs.
Four-dimensional CT (4DCT) for imaging hyper-
functional parathyroid glands represents a good
example of the need to carefully assess the balance
between risks and benefits. The dose absorbed by
the parathyroid is 57.5 times higher (92 vs 1.6 mGy)
on average with 4DCT than with sestamibi scan-
ning.9
Therefore, 4DCT must be used with caution.9
However, a conservatively estimated absorbed dose
of 27 mSv received in a 4-stage 4DCTexaminationin-
creases a patient’s annual cancer risk by only
0.019%.10
Given the very small risk, this particular
scenario has a favorable risk–benefit ratio.10
Reducing the 4DCT examination from 4 stages to
3 would diminish the effective dose to approxi-
mately 21 mSv without lowering the examination’s
accuracy.11
Reducing the examination to 2 stages,
however, would drastically lower the likelihood of
accurately localizing the abnormality.11,12
Overall,
the potential benefits of quality 4DCT scanning to
localize a parathyroid disease can outweigh the risks.
The safety of each patient ultimately rests on
their clinician’s educated assessment of those risks.
Clinicians should ensure that all diagnostic imag-
ing examinations are of high quality and need not
be repeated. As endocrine surgeons, we can help
our referring physicians by encouraging them to
allow us to order scans based on quality and
necessity of ‘‘roadmapping’’ the case, not for
diagnostic purposes. We can help our patients by
being knowledgeable about radiation risks so that
we can effectively inform a patient with sporadic
primary hyperparathyroidism that the risks of
performing a good, quality, diagnostic 4DCT ex-
amination are minimal compared with the benefits
of localizing an adenoma. The importance of
accurate localization to help facilitate cure and
eliminate future studies can ensure that diagnostic
imaging procedures do not needlessly compromise
patient safety.
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Table I. Typical effective radiation doses from
common diagnostic imaging examinations13
Examination
Typical effective
dose (mSv)
Range
(5th–95th
percentile)
95th/5th
percentile
ratio
Ultrasound 0.0 — —
X-ray
Skull 0.03 0.012–0.06 5.0
Chest 0.02 0.008–0.037 4.6
Abdomen 0.7 0.26–1.4 5.4
Pelvis 0.7 0.3–1.3 4.3
CT
Head 2.0 0.9–3.0 3.3
Chest 8.0 2.4–16.0 6.7
Abdomen 10.0 4.0–18.0 4.5
Pelvis 10.0 4.0–18.0 4.5
Table II. Levels of radiation for various types of
exposure from diagnostic imaging examinations13
Exposure
Approximate
effective
dose (mSv)
Radiation
equivalent
Ultrasonography 0.0 —
Working as an
international flight
attendant for 1 y
(600 flights)
4 2 head CT scans
Natural background
radiation (1 y)
2.4 120 chest x-rays
Chest x-ray 0.02 3 international
flights
CT
Head 2.0 100 chest x-rays
Chest 8.0 4 head CT scans
Abdomen 10.0 4.2 y of natural
background
radiation
4DCT (4-stage) 27.0 8 y of natural
background
radiation
CT, Computed tomography.
Surgery
December 2014
1298 Ray et al

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Surgery
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