Risk of childhood cancer and early life exposure to diagnostic radiation
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
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.
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.
Rapid Response:
Risk of childhood cancer and early life exposure to diagnostic radiation
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