Review

Medical Principles
and Practice Med Princ Pract 2012;21:508-515 Received: July 14,2011
DOI: 10.1159/000337404 Accepted after revision: January 24,2012
Published online: March 30,2012

Radiation Dose Features and Solid Cancer

Induction in Pédiatrie Computed Tomography
Ernest K.J. Pauwels^- ^ Michel H. Bourguignon"^-^
^Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; ''Department of
Nuclear Medicine, Pisa University Medical School, Pisa, Italy; '^Department of Biophysics, Université de Versailles Saint
Quentin en Yvelines, and "^Autorité de Sûreté Nucléaire, Paris, France

Key Words Introduction

Computed tomography • Radiation dose • Cancer
induction • Pediatrics • Cancer risk Over the past several decades, technical developments
in computed tomography (CT) have provided advances
in temporal and spatial resolution. This has resulted in
Abstract shorter scanning time and thinner slice thicknesses. It
Over the past two decades technical advances and improve- has led to an increased number of diagnostic applications
ments have made computed tomography (CT) a valuable and number of scans per patient as well as an increase in
and essential tool in the array of diagnostic imaging modali- the number of installed CT scanners worldwide. Indeed,
ties. CT uses ionizing radiation (X-rays) which may damage in 2009 it was reported that every day more than 19,500
DNA and increase the risk of carcinogenesis. This is especial- CT scans were performed in the USA [1]. Mettler et al. [2]
ly pertinent in pédiatrie CT as children are more radiosensi- reported in the same year that in 2006, 67 million CT
tive and have a longer life expectancy than adults. The pur- scans were performed in the US, which accounted for
pose of this paper is to review and elucidate the potential 17% of the total number of medical imaging procedures.
harmful effects of ionizing radiation in terms of solid cancer Hence, the growth of CT examinations is evident when
induction from pédiatrie CT scanning. In the light of scien- compared with the number of CT scans in 1980-1982,
tific and technical developments, we will also discuss the which was estimated to be 2-3.5 million per year. This
possible strategies and ongoing efforts to reduce CT radia- increased utilization of CT, however, comes with a price:
tion exposure in pédiatrie patients. In this context, we will the US per capita annual effective dose from CT has in-
not ignore the fact that a well-justified CT scan may exceed creased from 0.016 mSv (1980-1982) to 1.47 mSv (2006)
its risk and have a favorable impact. [2]. Similarly, the per-capita annual effective dose from
Copyright © 2012 S. Karger AG, Basel diagnostic imaging procedures has increased about a six
fold from about 0.5-3.0 mSv, which implies that about
half of the radiation exposure is due to CT scanning. Sa-
detsky [3] gathered data from the USA and Europe and
E.K.J.P. wishes to dedicate this paper to Professor Dr. Ad van Voort- demonstrated in 2007 that although CT scanning only
huisen, a worthy individual, supportive colleague, and visionary ra- constituted 5-10% of all imaging procedures, it contrib-
diologist, on the occasion of his 80th birthday. uted 40-67% of the total radiation burden.

KARGER ©2012S. Karger AG, Basel Prof. Emeritus Dr. E.K.J. Pauwels
1011-7571/12/0216-0508$38.00/0 Via di San Gennaro 79/B
Fax+41 61 306 12 34 IT-55010 San Gennaro (Italy)
E-Mail karger@karger.ch Accessible online at: E-Mail ernestpauwels@gmail.com
www.karger.com www.karger.com/mpp
 Ideally, the acquisition of CT images occurs according terms of solid cancer induction from pédiatrie CT scan-
to standardized validated protocols endorsed by national ning. Based on scientific and technical developments, we
and/or international professional organizations, enabling will also discuss the possible strategies and ongoing ef-
the demonstration and differentiation of abnormalities. forts to reduce CT radiation exposures in pédiatrie pa-
However, there is a lack of standardization and a wide tients. However, we should point out the fact that a well-
variation of acquisition parameters and dose variations justified CT scan could exceed the risk from exposure yet
for the same CT examination [4-6]. This is illustrated by have a favorable clinical impact. First, however, we will
the management of noise in the image. A proper image give very brief descriptions of some basic principles of
interpretation requires a noise level that is neither high physics regarding CT imaging and units of radiation
nor low. Obviously, images with high noise levels, associ- dose.
ated with low radiation intensity, may be nondiagnostic.
Lower noise levels may be obtained by adjusting the grey Basic Principles of Medical CT
scale of the area of interest, but image degradation may Unlike ultrasound and magnetic resonance imaging
occur resulting in diagnostic inaccuracies. This noise-as- (MRI), CT uses ionizing radiation. During a CT scan, a
sociated problem may be overcome by applying high lev- rotating X-ray source passes X-rays through a body part
els of radiation intensity, which minimizes image noise of the patient while often the table on which the patient
and image quality. This approach, together with the ris- lies moves in order to cover the part of the anatomy of
ing number of CT scans, has raised concern for the life- interest. Opposite the X-ray source, a detector unit is
long risk of cancer induced by radiation exposure from mounted and both the source and the detector rotate
CT imaging [7, 8]. As children have a longer life expec- around the patient in a circular way to produce cross-
tancy than adults, pédiatrie studies may have long-term sectional images. The transmitted X-rays are then con-
consequences. Moreover, the radiation sensitivity of chil- verted into electrical signals that are collected from
dren is higher than adults [9]. Their rapid growth is as- different angles and are reconstructed by specialized
sociated with a high rate of cell division, which is the most software (filtered backprojection and/or iterative recon-
risky phase for induction of DNA damage. Besides, in struction) to create a three-dimensional presentation of
children the biological process for the identification of tissue densities relative to water in the body. Finally, this
mutated cells and the induction of repair mechanisms is procedure results in artificial cross-sectional coupes
not very effective yet. In this context, it is important to ('slices') of the scanned volume. The slice thickness can
know that there were at least 6.5 million CT examinations be in the order of millimeters, thus providing a detailed
performed on children in the US in 2006. This corre- set of slice-images. Modern technology allows for a com-
sponds to about 10% of all CT examinations [10]. Conse- plete rotation in less than 0.5 s and a complete recon-
quently, in the early 2000s, both researchers and the Fed- struction in tenths of a second. These characteristics
eral Drug Administration (FDA) called attention to the have made CT a very valuable tool for high patient
necessity of reducing the risk of radiation exposure from throughput and accurate diagnosis, longitudinal mea-
CT for pédiatrie patients [11, 12]. The lifetime solid can- surements of disease progression and monitoring of
cer risk estimates for those exposed as children might be treatment.
a factor 2-3 times higher than the estimates for the gen-
eral population [13]. In addition, a recent report demon- Dosimetric Units Used in This Paper
strates a statistically significant dose-related increase in In radiological sciences the absorbed dose is relevant,
the incidence of solid cancer for those exposed in the first as it refers to the amount of the total energy absorbed by
6 years of life, similar to the time of the atomic bombing the irradiated tissue. It is measured in joule per kilogram
in Japan. The relative risk of cancer, averaged for attained and its measuring unit is the gray (Gy). To take into ac-
age (12-54 years), gender and dose categories is estimated count the biological effect of a given radiation, the con-
to be 1.4 for those exposed in early childhood [14]. Like- cept of equivalent dose has been introduced. The mea-
wise, the WHO has documented an increased incidence surement unit is the Sievert (Sv), defined as the absorbed
of thyroid cancer in irradiated children under 18 years of dose multiplied by a quality factor that weights the radi-
age following the Chernobyl accident (http://www.who. ation-specific biological effects by various sources of ra-
int/mediacentre/factsheets/fs303/en/index.html). diation. For x-rays, as used in CT, this quality factor is 1,
The purpose of this paper is to review and elucidate therefore the equivalent dose equals the absorbed dose
the potential harmful effects of ionizing radiation in and has the same numerical value.

Cancer Induction Associated with Med Princ Pract 2012;21:508-515 509

Pédiatrie CT
 In order to estimate the biological effect on different vide, leading to genomic instability and eventually to on-
tissues, the effective dose is used. This is based on a spe- cogenic transformation with potential cancer develop-
cific weighting factor that is applied to each tissue. The ment [16-18].
effective dose is the sum of the weighted equivalent doses
of all organs in the body. The measurement unit is also Biomarkers of Chromosomal Damage
the Sievert (Sv). Thus, the effective dose takes into ac- The micronucleus assay is frequently used as a bio-
count both the type of radiation and the type of tissue. marker for chromosomal damage. It is a low-cost test for
Hence, the effective dose makes a comparison possible the study of damage of the genome and considered as an
between various imaging modalities using ionizing ra- intermediate endpoint of carcinogenesis due to radiation
diation. The radiation dose may vary for each CT scanner exposure [19]. Micronuclei in the cell originate from mis-
model and each X-ray tube setting, as for kVp and mAs, repaired, unrepaired DNA lesions or from chromosomal
as well as table speed, tube rotation time and pitch (the malsegregation due to mitotic malfunction. The resulting
latter defined as the ratio of the distance that the table formation of micronuclei, whether through chromosomal
advances in one rotation in mm to the nominal slice rearrangement, or altered gene expression (aneuploidy),
thickness in mm). has been linked to genotoxic events and chromosomal
The radiation output of a specific clinical CT exami- DNA damage [20]. A large epidemiological study has
nation is commonly presented as the computed tomo- shown that the frequency of a micronucleus in peripheral
graphic dose index (CTDI) multiplied by the scan length. blood lymphocytes can predict the risk of cancer in hu-
The CTDI (volume) refers to the absorbed dose in a spe- mans [21]. For radiological procedures in children with
cific volume (usually in units of mGy) and depends complex congenital heart disease, the micronucleus test
strongly on the patient's anatomy. For reasons of stan- has been used as a biomarker for chromosomal damage. A
dardized comparison between different scanner designs, study by Ait-Ali et al. [22] in 59 children showed that the
the CTDI, 100 represents a basic radiation dose parame- main contribution of dose came from interventional pro-
ter that refers to the radiation exposure measured in an cedures: 84% and CT 11%, with the median micronucleus
ionization chamber of 100 mm length. value increasing significantly after these procedures from
6 per thousand (before) to 9 per thousand (after); p = 0.02.
Another test for chromosomal damage is based upon
Biological Effects of Low-Energy X-Rays the phosphorylation of the histone H2AX on serine 139,
which was at the time called gamma-H2AX. Initiated by
A Brief Survey of Low-Dose Radiation Damage a double-strand break, the phosphorylation of hundreds
In contrast to high-dose radiation, low-dose radiation to thousands of H2AX molecules form foci at the break
(below 100 mGy) may exert a dual genotoxic response in sites that can be detected by fluorescence microscopy.
exposed tissues and cells. In mammalian cells, low-dose This assay has proven to be useful in basic research and
ionizing radiation causes damage mainly to DNA, as is clinical studies. For instance, lymphocytes from blood of
the case with high-dose radiation. The other phenome- patients undergoing CT examination or X-ray angiogra-
non involves an adaptive protection against the harmful phy have shown that individuals repair DSBs to back-
effects and has not been observed at high doses. This re- ground levels in less than 24 h [23, 24]. A recent study by
sponse has also been observed as a reaction to endoge- Beels et al. [25] has demonstrated that a CT system oper-
nous and exogenous toxins other than radiation. ating at higher dose settings causes a significantly higher
Radiation-induced DNA damage originates from both number of radiation induced gamma-H2AX foci (a 2.1
reactive oxygen species created along the radiation track times higher dose-length product is associated with a 2-3
and direct electron interaction with DNA. The damage times higher number of foci). The same study also dem-
to DNA typically causes single-strand breaks, double- onstrated that the number of foci showed a systematic
strand breaks (DSBs) and crosslinks. This damage can be increase versus blood dose. These and other studies [26,
repaired on a minute time-scale after the damage has oc- 27] confirm that this assay is a useful biodosimetric
curred by activation of DNA repair genes. With a delay of marker for basic research and human studies.
several hours, the damaged cells with unrepaired or mis-
repaired DNA can be removed by apoptosis, necrosis and The Linear Nonthreshold Model
appropriate immune responses [15]. However, some cells Epidemiological data from the atomic bomb survivors
may 'escape' from these protective mechanisms and di- in Japan has provided risk estimates for moderate to high

510 Med Princ Pract 2012;21:508-515 Pauwels/Bourguignon

doses above 50-100 mGy. At these doses, there is ample sent [40]. Finally, natural background radiation amounts
evidence to suggest that excess cancer risk is linearly re- to 2-3 mSv per year, depending on the geographical area.
lated to the effective dose. At present there are no epide- It is therefore conceivable that background radiation also
miological data that allow for solid estimates below this gives rise to carcinogenesis, which would be difficult to
level and the subject is under continuous debate. How- differentiate from the effect of a single diagnostic proce-
ever, for practical regulatory purposes, a linear model has dure with low-level radiation.
been adopted for these low doses. In addition, it is hy-
pothesized that there is no threshold for stochastic ef- Cancer Risk Estimates at Doses below 100 mSv
fects. This is the linear nonthreshold (LNT) model [28], Which risk estimate would be appropriate on the basis
which has as its starting point that any radiation is poten- of present knowledge? As yet, the public summary (avail-
tially harmful and requires some kind of protection. The able at www.nap.edu) of the Biological Effect of Ionizing
LNT model starts from an excess cancer risk of 5% per Sv Radiation (BEIR) VII 2006 report endorses the LNT hy-
effective dose. Although the International Committee on pothesis but indicates that at doses below 100 mSv 'statis-
Radiation Protection (ICRP) has stated in its publication tical limitations make it difficult to evaluate cancer risk
103, article 161 in 2007 [29] that this risk factor is not in humans'. The report relies on a life-time risk of 5 in 100
valid to evaluate low-level radiation excess cancer risk of mortalities from cancer due to an effective dose of 1 Sv.
a population, some authors [30, 31] used this risk factor This risk would translate into a risk of 0.05% (1 in 2,000)
and have reported an excess of cancers due to medical for an individual who received a dose of 10 mSv. In this
diagnostic exposures. Berington de Gonzales et al. [30] context, Cardis et al. [41], who conducted a 15-country
estimated that 29,000 future cancers could be related to study following 407,000 radiation workers who received
CT scans performed in the US in 2007. Likewise, Hall and an average dose of 19 mSv for over 20 years, reported an
Brenner [31] predicted 750 fatal cancers from CT exami- excess all-case mortality, mainly due to an increase of
nations performed in the UK in 2006. 0.04% in mortality from all cancers. The excess relative
Various arguments point to an overestimation of the risk rose as the radiation dose increased. It should be not-
risk by the LNT model. First, carcinogenesis with at least ed that the average dose received by these radiation work-
3 steps of induction, promotion and progression is obvi- ers is well in the dose range of an average CT examination
ously a nonlinear process. Second, a long-term study ranging from 2-20 mSv.
among British radiologists showed lower cancer mortal- Indeed, the previously mentioned study by Ait-Ali et
ity than suggested by extrapolation of the atomic bomb al. [22] demonstrated that the estimated life-time attrib-
response data [32]. Third, epidemiological studies re- utable risk of fatal cancer was 0.06% for a 0- to 15-year-old
garding large populations in geographical areas with male receiving 7.1 mSv and 0.12% for a 0- to 15-year-old
high natural background radiation failed to demonstrate female receiving 9.4 mSv. In addition, it was found that
any effect [33]. Fourth, at low dose rates, biological sys- the risk is 1.9-2.0 times higher for a child of 1 year than
tems are stimulated to remove damaged DNA by recruit- for a 15-year-old individual. These risk estimates were
ing homeostatic control systems [34]. based on a micronucleus assay in children with congeni-
By contrast, some findings suggest that there is an un- tal heart disease, 95% of whose total collective dose was
derestimation of the risk by the LNT model. First, various attributed to diagnostic catheterization (average effective
in vitro experiments have confirmed radiation responses dose 4.6 mSv), interventional catheterization (average ef-
in neighboring cells, called the bystander effect [35]. Sec- fective dose 6 mSv) and CT (average effective dose 4 mSv).
ond, genomic instability caused by radiation may cause
amplification of chromosomal abnormalities after vari- Radiation Risk in Children due to CT
ous cell divisions, although these cells have not been ir- The above-mentioned 15-country study has added
radiated [36]. support for the LNT model in the sense that it suggests
Finally, although it is thought that cancer arises from the absence of a threshold for carcinogenesis. Further
a single hit to nuclear DNA, there is also evidence that support for the no-threshold hypothesis has been pro-
non-DNA targets within the cell maybe involved [37,38]. vided by Muirhead et al.'s [42] study in which a statisti-
In addition, hypersensitivity to radiation exists in appar- cally significant increase in the grouping of malignant
ently normal individuals [39]. In these individuals, reac- neoplasms occurred as the radiation dose increased. The
tive repair mechanisms and generation of inflammatory analysis was performed using the National Registry of
cells elicited by radiation damage may be delayed or ab- Radiation Workers in the UK and, as in the 15-country

Cancer Induction Associated with Med Princ Pract 2012;21:508-515 511

Pédiatrie CT
 study, on a large group of men and women (n = 174,541). appropriate quality assurance regarding the functioning
Because these two large studies were carried out in work- of the CT scanner and specific training for professionals
ers, no information on the effect of radiation on children [49]. This task has been addressed by developing a web-
has been reported. However, a case-control study (part based quality improvement program presented as an on-
of the UK Childhood Cancer Study) by Rajaraman et al. line tutorial accessible on the Image Gently website that
[43] showed further evidence of possible excess risk of enables radiologists and technologists to perform ade-
cancer, even at doses lower than those associated with quate and safe CT for pédiatrie patients. For US-based
CT scanning. Exposure of patients in early infancy (0- radiologists, this program also complies with new re-
100 days at time of investigation 14 years or younger) to quirements of the American Board of Radiology for
diagnostic radiology (247 procedures in 170 partici- maintenance of certification [50, 51]. The program pro-
pants) was associated with a slightly elevated risk for all motes public awareness and is also meant to educate re-
childhood solid cancers (OR 1.16, 0.83-1.62), but the as- ferring physicians about the potential radiation-associat-
sociations were not statistically significant. Neverthe- ed risks from CT scanning, with an emphasis on pédiat-
less, an absence of significance should not be interpreted rie scanning. It stresses the need to justify the examination
as evidence of a lack of risk. For example, a study by and make a comparative assessment of CT on the one
Chodick et al. [44] found an excess risk of CT-related life- hand and ultrasound and/or MRI on the other to avoid
time cancer mortality for patients scanned before age 15 unnecessary pédiatrie radiation exposure.
years of age. In a first approximation following the meth- In 2008, the European Commission issued the Euro-
od of risk estimation put forward by Brenner et al. [45], pean Guidance on Estimating Population Doses from
it was suggested that the highest excess risk (0.52%) oc- Medical X-Ray Procedures (Radiation Protection No.
curred for CT in children under 3 years of age. A recent 154; available at www.ddmed.eu). For pédiatrie patients,
study by Kuhns et al. [46] used the BEIR VII 2006 report this report gives further significance to a specifically tai-
to estimate the lifelong risk for pédiatrie patients who lored examination protocol using dose reduction fea-
underwent CT scanning for renal calculus detection. tures such as the number of CT scans, scan length, field
The authors summarized their findings as follows: the of view, tube voltage, tube current, tube rotation time,
ratio of the risk for any abdominal and pelvic cancer due beam collimation, table speed, pitch, CTDI (volume) and
to a CT examination for calculus detection to the risk of dose-length product. In addition, patient dose reports,
a naturally occurring cancer over lifetime of the child is preferably in standard DICOM format, should be docu-
estimated to be 2/1,000 (for children 15 years of age of mented.
both genders at the time of examination) and 3/1,000 (for
children of both genders, 10 years of age or younger). Recent Technical Developments regarding Dose
They estimated the CT radiation dose (3.6-5.8 mSv) to Reduction in Pédiatrie CT
be approximately equivalent to 1-2 years of background Various articles on cancer induction by CT scanning
radiation. Raelson et al. [47] also used the BEIR VII2006 have caused a negative public perception and even led to
report to estimate the stochastic effect of radiation expo- refusal of the examination by patients or relatives. One
sure in children (0-17 years of age) who underwent CT article [10] has stated that 1.5-2.0% of cancers in the US
scanning for primary neurovascular diagnosis and re- may be caused by ionizing radiation used during CT ex-
ceived an average dose of 35.3 mSv. These authors esti- amination. Other authors, as previously mentioned, have
mated the number of excess cancer cases expected from estimated that approximately 29,000 future cancers could
100,000 exposed children (321 for males and 388 for fe- be related to CT scans performed in the US in 2007 [30].
males) amounting to an overall increase of about 0.35% Whether true or not, these articles have stimulated the
to the lifetime attributable risk of cancer. development of new technology platforms to minimize
The data mentioned above justified the need to apply the dose of CT radiation. These efforts, summarized be-
a 'universal' system to reduce the radiation dose for chil- low, are part of an ongoing process to find an appropriate
dren and adults. In this respect the ALARA ('As Low As balance between the quality of the produced image and
Reasonable Achievable') principle has been widely ac- the protection of the patient.
cepted. It emphasizes the fact that unnecessarily high One development involves the modulation of the tube
doses should be avoided. This can be achieved by both current and adjustment of the intensity of the irradiation
judicious use of CT and adjusted, tailored CT techniques to the anatomy of the patient; that is, according to patient
[48]. The ALARA principle can only work if there is both attenuation. It is a most practical way of reducing the CT

512 Med Princ Pract 2012;21:508-515 Pauwels/Bourguignon

dose and this technology can result in a dose reduction of to below 10%. In a series of adult cases prospective ECG
36-60% in adults [52]. However, some caution is need- gating (n = 57) was compared to retrospective ECG gating
ed for pédiatrie imaging with modulated tube current (n = 29) by DeFrance et al. [58]. The authors found a mean
achieved by automatic exposure control, as measure- effective dose reduction of 59.2% using prospective gat-
ments in a pédiatrie anthropométrie phantom have dem- ing compared to retrospective gating with a mean dose of
onstrated a significant dose inerease for salivary glands 6.9 mSv for the prospective technique. Only in 0.7% of the
(28-45%), bladder (22-51%) and ovaries (24-70%) in rela- images was the quality judged as noninterpretable. An-
tion to the high density of the base of the skull and the other study [59] compared both gating methods and
pelvie bones, respeetively [53]. In general, CT parameters reached a reduction of 65%, whereas in 2.6% (prospective
for pédiatrie patients need to be adjusted on the basis of gating) and 0.9% (retrospective gating), the images could
the indieation of the study, the age, and the body size, not be interpreted due to low quality. Also, studies by Ar-
proper positioning of the child, the use of tube filters and noldi et al. [60] and by Horiguchi et al. [61] mentioned a
tailored pitch. dose reduction around 60%, but Young et al. [62] stated
A newer way of achieving dose is based upon iterative that the prolonged data acquisition time may cause arti-
reconstruction. With regard to low dose CT associated facts in pédiatrie seanning because breath-hold cannot be
with poor noise statistics iterative reconstruction aims to maintained. Indeed, a recent study in 20 children who
reconstruct an optimal image using iterative algorithms. underwent prospective ECG-triggered sequential dual
With advancing computer capabilities this technology source CT examinations found that in 4 patients breath-
has become available as opposed to filtered backprojec- ing artifacts were present [63].
tion. For adults, an abdominal dose reduction of 23-66% Another significant advance is the recent availability
has been reported [54]. A 'blending' of iterative recon- of a 320-slice multidetector CT scanner which allows ax-
struction and filtered backprojection may lead to a 36% ial volumetric scanning of a 16-cm long range in a single
reduction in radiation dose for a 2- to 3-year-old child 0.35-second rotation with an acquisition configuration of
while adequate diagnostic quality has been maintained 320 X 0.5 mm, avoiding any over-ranging and making
[55]. Iterative reconstruction has been successfully used breath-holding unnecessary [64]. Al-Mousily et al. [65]
in nuclear medicine where low-photon numbers create reported on the use of this scanner in the evaluation of
noisy images. Briefly, iterative reconstruction uses mea- congenital heart disease in 22 infants and young chil-
sured projections to construct an image. In the following dren, 14 of whom were examined without cardiac gating
step, a 're-projection' process calculates new projections and 8 with prospective gated image acquisition. In the
simulating a CT measurement on the basis of the original nongated protocol, the effective dose was 1.8 ± 0.7 mSv.
image, then a corrected image is constructed using the The protocol using cardiac gating demonstrated a further
original image and the calculated projections. The calcu- dose reduction to 0.8 ± 0.4 mSv. This effective dose,
lation proceeds in a loop-wise mode to update the image combined with the fact that breath-holding and sedation
by moving data back and forth. The final result is en- are not necessary, enables CT to play a greater role in the
hanced spatial resolution in image areas with higher con- management of pédiatrie eongenital cardiovascular dis-
trast and reduced noise in areas with low contrast. It is ease and most likely also in other pédiatrie disorders.
especially useful in CT to enhance images acquired dur-
ing low radiation dose procedures [56].
The dose reduction techniques have been noticeably Epilogue
increased in cardiology, particularly in children with
congenital cardiovascular disease [57]. A significant ad- Even more than adults, for ehildren the benefit of eaeh
ditional dose reduction can be achieved by ECG trigger- imaging study using ionizing radiation should be bal-
ing ('ECG gating'), which is used to adjust the tube cur- aneed against the long-term risk of eaneer development.
rent. Prospective ECG triggering that targets the end-sys- Aeeording to the widely aeeepted LNT model, there is no
tolic phase is possible in patients with a variable heart safe dose, but present knowledge about eaneer risk due to
rate, roughly between 60 and 110 bpm. The end-systolic diagnostie radiation does not give any reason for alarm.
phase is relatively constant for these heart rates. An algo- However, the effeetive dose for ehildren who are repeat-
rithm that predicts the 'phase of interest' of the cardiac edly examined may well be above values of 50 mSv. This
cycle drives the tube current to 100%, whereas during the is no longer an effeetive dose that ean be eategorized in
remaining phase of the cycle, the current can be reduced the low dose range. These doses fall within the realm in

Cancer Induction Associated with Med Princ Pract 2012;21:508-515 513

Pédiatrie CT
whieh inereased eaneer risk due to ionizing radiation is only the indicated region', 'involve medical physicists to
well-established, and radiologists and referring elinieians monitor pédiatrie CT teehniques', and 'involve teehnolo-
should be vigilant about the eumulative risk of radiation gists to optimize seanning'. CT seanners should offer
exposure. speeial teehnology for pédiatrie imaging [66]. The IAEA
In this respeet, the 'Image Gently' Campaign, an ini- Radiation Proteetion of Patients supports the Image Gen-
tiative of the Allianee for Radiation Safety in Pédiat- tly eampaign and helps health professionals aehieve safer
rie Imaging (www.pedrad.org/assoeiations/5364/ig), was use of radiation for the benefit of ehildren and their
launehed in early 2008 to urge a signifieant reduetion in parents (www.iaea.org/RPOP/RPOP/Content/Arehived-
the amount of radiation used for pédiatrie studies. Im- News/image-gently).
portant adviee ineludes 'scan only when necessary', 'scan

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