Early life exposure to diagnostic radiation and ultrasound scans and risk of childhood cancer: case-control study
BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d472 (Published 10 February 2011) Cite this as: BMJ 2011;342:d472
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In the field of clinical radiology, it is important to safeguard both the patient and the hospital staff that administer the services to patients. This is mainly because patients as well as hospital staff are exposed to harmful radiations such as x-rays, which are used for diagnostic imaging service.
Clinical radiology mainly involves the use of harmful radiation in diagnosis. Therefore, there is a need to improve quality and healthcare safety in this field. In order to improve this safety standards there are a number of critical elements that need to be brought together. The patient is at the centre of the improving quality and healthcare safety. Other factors included education, methods, and tools to achieve the objectives, care coordination, health services, physicians, and third party individuals. There is a need to bring all this elements together in order to implement excellent policies that will ensure improved quality and safety.
There is a need for different key players to work together for safety in order for the aims to be achieved. These include healthcare players, the government, and academia. All the players have to be a part of the quality and healthcare safety in clinical radiology.
Competing interests: No competing interests
Failure or reluctance to image pregnant women is a factor
contributing to maternal mortality (1). Rajaraman et al state that there
is an increased risk of childhood cancer and leukaemia from x ray imaging
of the mother during pregnancy (2). It should be noted that the risk is
small and does not reach statistical significance. Although controls were
similar for many identified confounding factors, a family history of
cancer was not accounted for. Furthermore, most x-rays were performed for
obstetric pelvimetry, a practice that is outdated. The results from this
study are therefore not applicable to modern day imaging of pregnant
women. The fetal effects of plain chest and bone x-rays and computerised
tomography of the head and chest are of more relevance to current
practice. With lead shielding the radiation dose to the fetus is minimal
and far less than plain x rays of the abdomen/pelvis (3).
The conclusion of the study that there are "possible risk of cancer
from radiation at doses lower than those associated with commonly used
procedures such as computerised tomography scans" is weak given the
results do not reach statistical significance. This sends out the wrong
and potentially dangerous message that imaging in pregnancy is harmful.
Scaremongering and implying that vulnerable, sick pregnant women may be
'harming their baby' if they undergo radiological procedures is a
retrograde move and contradicts recommendations from the latest
Confidential Enquiries into Maternal Deaths (4). CT scans to aid diagnosis
of potentially fatal conditions such as subarachnoid haemorrhage,
pulmonary embolus or aortic dissection should not be withheld for
unsubstantiated concerns about fetal risk.
Dr Kenneth Hodson, Academic Clinical Fellow in Obstetrics and
Gynaecology, Northern Deanery
Mr Jason Waugh, Consultant in Maternal Medicine, Royal Victoria
Infirmary, Newcastle upon Tyne
Professor Catherine Nelson-Piercy, Consultant Obstetric Physician at
Guy's & St Thomas' Foundation Trust and Queen Charlotte's &
Chelsea Hospital and Professor of Obstetric Medicine at King's College
Hospital
References:
1. Saving Mothers' Lives: Reviewing maternal deaths to make
motherhood safer - 2003-2005. Confidential Enquiry into Maternal and Child
Health; December 2007
2. Rajaraman P et al, Early life exposure to diagnostic radiation and
ultrasound scans and risk of childhood cancer: case-control study. BMJ
2011;342:d472
3. Protection of Pregnant Patients during Diagnostic Medical
Exposures to Ionising Radiation: Advice from the Health Protection Agency,
The Royal College of Radiologists and the College of Radiographers. Health
Protection Agency; March 2009
4. Saving Mothers' Lives 2006 - 2008, Centre for Maternal and Child
Enquires. http://www.cmace.org.uk/Publications-Press-Releases/Report-
Publications/Maternal-Mortality.aspx
Competing interests: No competing interests
At the outset, I would like to congratulate BMJ & Prof. Preetha
Rajaraman and the group for a brilliant study.
It is always expected that cases and control in Case-control study face
similar diagnostic procedures. Hence selection of control becomes very
difficult. In the present study, methodology section needs to be more
elaborative for this important and vital component of Case- Control study
which influences its implication for practice. Many times, case control
studies have better diagnostic methods applied to cases while control only
has no visible / apparent complaint with respect to disease. This may be
due to ethical reasons but in such cases, control should be those
participants who are representative for the cases and have undergone the
similar diagnostic procedures but have negative results.
Competing interests: No competing interests
As known to all, radiological protection of pediatric and pregnant
patients undergoing medical diagnostic imaging procedures involving
ionizing radiation has always received special attention. This is due to
the fact that children and embryo/fetus have higher radiation sensitivity
and increased likelihood for radiation-induced cancer manifesting in many
more years of their life than adults.1 Considering the potential risk of
stochastic effects (incurring cancer or heritable effects) in children,
IAEA (International Atomic Energy Agency) and ICRP (International
Commission on Radiological Protection) have paid essential attention to
the medical radiation for children. In continuation with similar networks
established in Europe and Asia in 2010, IAEA is plan to establish a
network of medical professionals on "radiation protection of children" for
Latin American Countries in 2011.2 The main purpose is to create network
with specific tasks to promote radiation protection actions in children.
In the latest papers about the association between early life
exposure to diagnostic radiation and risk of childhood cancer, Rajaraman
et al. have done excellent investigations and their findings indicate
possible risks of cancer from radiation at doses lower than those
associated with commonly used procedures such as computed tomography
scans, suggesting the need for cautious use of diagnostic radiation
imaging procedures to the abdomen/pelvis of the mother during pregnancy
and in children at very young ages.3 They have provided valuable data for
the estimation of the risk of radiation carcinogenesis in childhood.
However, as a radiobiologist, I think the data about radiation dose
of all the included populations is essential in this study. In ICRP
recommendations, for the risk of cancer, the radiation dose is mentioned
and necessary. The induction of deterministic effects (harmful tissue
reactions) by radiation is generally characterized by a threshold dose.
Above the threshold dose the severity of the injury, including impairment
of the capacity for tissue recovery, increases with dose,4 this also
called dose-response relationship. Unlike deterministic effects, the
induction of stochastic effects by radiation has no threshold dose and
dose-response relationship. The morbidity of cancer induced by radiation,
one of the stochastic effects, has no threshold dose and dose-response
relationship, but the risk of cancer has dose-response relationship. So
the detailed dose level is very important in this study. In the case of
cancer, epidemiological and experimental studies provide evidence of
radiation risk albeit with uncertainties at doses about 100 mSv or less.4
In the new ICRP recommendations, the practical system of radiological
protection continue to be based upon the assumption that at doses below
about 100 mSv, a given increment in dose will produce a directly
proportionate increment in the probability of incurring cancer or
heritable effects attributable to radiation.4 This dose-response model is
generally known as 'linear-non-threshold' or LNT. This view accords with
that given by UNSCEAR (United Nations Scientific Committee on the Effects
of Atomic Radiation) (2000).5
Furthermore, I think there are some factors should be considered in
this study. The estimation of the risk of radiation carcinogen is a very
complicated procedure. So many confounded factors may affect the results.
So, the factors should be considered in the statistical analysis:
(1) Other exposure factors except radiation in the investigated
population. The authors have considered the variables as potential
confounders: maternal age, smoking, socioeconomic status, pregnancy order,
pre-eclampsia, anaemia, multiple pregnancy, child's birth weight, and
admittance to the neonatal intensive care unit. But other environmental
exposure factors should be considered essentially: indoor air, other
chemical, industrial and agricultural pollution in their living
environment at the period of infants and pregnancy.
(2) The family medical history of cancer. The family affectability of
cancer is also a confounder in the risk estimation and it should be
matched in the exposure and control groups.
Rajaraman et al. have found a slight increase in risk after in utero
and early infancy (0-100 days) exposure to diagnostic x rays for all
cancers leukaemia, but this was not statistically significant.3 This is
very valuable data for protection of radiation and coincident with the
standpoint of ICRP: the life-time cancer risk following in utero exposure
will be similar to that following irradiation in early childhood.4,6
The term "diagnostic reference level" (DRLs) is now used in the
context of the optimisation of protection of patients undergoing medical
exposure. It is a mechanism to manage patient dose to be commensurate with
the medical purpose.4,6 This term also called "reference dose levels" in
pediatric patients. This may decrease the individual dose of the patients,
expect to reduce the risk of stochastic effects by radiation and may have
significant practical value in medical diagnostic imaging procedures. But
the protection of pediatric radiology didn't receive essential attention
in China, for example, the investigation for the diagnostic radiation
dose, estimation of risk, guideine for reasonable application of children
diagnostic radiation and optimisation of protection in medical exposures.
The findings of Rajaraman et al. remind us a stronger need in China and
many developing countries to justify diagnostic radiation examinations in
children and their optimization, formulate and spread the "reference dose
levels" is very eager.
Qiang Liu, associate professor of radiobiology, Yan Wang, research
fellow, Li Qing Du, post-doctoral fellow, Jia Cao, doctoral fellow, Hong
Wang, doctoral fellow, Feng Hua Chen, investigator, Fei Yue Fan, professor
of radiobiology
Institute of Radiation Medicine, Chinese Academy of Medical Sciences
& Peking Union Medical College, Tianjin Key Laboratory of Molecular
Nuclear Medicine, 238, Baidi Road, 300192 Tianjin, People's Republic of
China
Correspondence to FY Fan: faithyfan@yahoo.cn
Acknowledgements: Our relevant work was supported by the National
Natural Science Foundation of China (No. 30800281), the Natural Science
Foundation of Tianjin (No. 10JCZDJC16900), the Doctoral Science Research
Foundation for High School of the National Education Ministry (No.
200800231051)
1 Muhogora WE, Ahmed NA, Alsuwaidi JS, Beganovic A, Ciraj-Bjelac O,
Gershan V, et al. Paediatric CT examinations in 19 developing countries:
frequency and radiation dose. Radiat Prot Dosimetry. 2010;140(1):49-58.
2 http://rpop.iaea.org/RPOP/RPoP/Content/UpcomingEvents/network-on-
radiation-protection-children.htm.
3 Rajaraman P, Simpson J, Neta G, Berrington de Gonzalez A, Ansell P,
Linet MS, et al. Early life exposure to diagnostic radiation and
ultrasound scans and risk of childhood cancer: case-control study. BMJ.
2011;342:d472. doi: 10.1136/bmj.d472.
4 ICRP. Recommendations of the International Commission on
Radiological Protection ICRP Publication 103. Ann ICRP 2007;37(2-4).
5 UNSCEAR. Sources and Effects of Ionizing Radiation. United Nations
Scientific Committee on the Effects of Atomic Radiation Report to the
General Assembly with Scientific Annexes.Vol. II: Effects. United Nations,
New York, NY. 2000.
6 Wrixon AD. New ICRP recommendations. J Radiol Prot 2008;28: 161-
168.
Competing interests: No competing interests
Re: Early life exposure to diagnostic radiation and ultrasound scans and risk of childhood cancer: case-control study
The case-control study by Rajaraman et al was insightful. It first confirmed the safety of ultrasound in utero and in early infancy, emphasizing the need to favour this non-invasive investigation over x ray and CT where possible, for example in the diagnosis of pelvic inflammatory disease or appendicitis. Secondly, it was reassuring to learn that use of x ray in utero and even in early childhood does not increase risk of cancer and leukaemia to a statistically significant extent. This comes with the warning that multiple exposure to X rays in early infancy may contribute to lymphoma development, although the numbers were small. The overall implication is that when the clinical need-to-risk ratio of an x ray is high, clinicians should not hesitate to request a diagnostic x ray in such subjects. Nonetheless, where resources permit, alternative modalities such as magnetic resonance imaging (MRI) must be considered. An extension to this study would be to include MRI, as well as to expand the study population to statistically confirm absolute risks of each modality. Once we have obtained the data, we can formulate more robust evidence-based guidelines for use of imaging in utero and in early infancy.
Competing interests: No competing interests