The Lancet Journal published a paper stating that the radiation exposure received from 2 to 3 computed tomography (CT)
scans of the head in childhood (aged under 15 years)—giving a cumulative
dose of around 60 mGy— can triple the risk of later developing brain
cancer, while around 5 to 10 such scans (cumulative dose around 50 mGy)
could triple the risk of developing leukaemia (with the differing number
of scans related to different absorption rates of the brain versus the
bone marrow and age at time of scanning).
There is some thing unique about this study. The risk estimate in this instance is directly derived. Dozens of such studies are going on all over the world. Normally, the researchers estimated the cancer risks from CT on the basis of risk estimates derived from A-bomb survivors. There were justifiable criticism against this approach.
You can access the paper at:
This paper is published Online First by The Lancet on 7 June 2012.
The absolute risk of these cancers occurring after CT is small but there is sufficient reason to keep the radiation doses from CT scans as low as possible.Dr Mark Pearce and Professor Sir Alan Craft, Newcastle University, UK; Professor Louise Parker, Dalhousie University, Halifax, NS, Canada; Dr Amy Berrington de González, National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD, USA, and colleagues conlude that if appropriate, alternative procedures, that do not use ionising radiation, should be considered. The study represents the culmination of almost two decades of research in this area, and is jointly funded by the UK Department of Health and NCI/NIH.
CT imaging is a unique medical radiation procedure. Use of this technology has increased rapidly in the USA and elsewhere, especially in the past decade. However, potential cancer risks exist due to the ionising radiation used in CT scans, especially in children who are more radiosensitive than adults.
In this retrospective study, the authors examined the records of close to 180,000 patients who underwent a CT scan between 1985 and 2002. It includes the records from the radiology departments of some 70% of the UK's hospitals. They extracted the number and types of CT scan from the records and estimated the dose absorbed in milli-Grays (mGy) by the brain and bone marrow in patients for each scan.
Then they linked the data to cancer incidence and mortality reports in the UK National Health Service Registry between 1985 and 2008. From this, they calculated excess incidence of leukaemia and brain tumours. The dose of radiation received by the brain and bone marrow varies by age, and body part scanned.
A total of 74 from 178 604 patients were diagnosed with leukaemia and 135 of 176 587 were diagnosed with brain cancer. The authors calculated that the relative risk of leukaemia increased by 0.036 per extra mGy received, whilst for brain tumours this increased risk was 0.023. Compared with patients who received a dose of less than 5 mGy, patients who received a cumulative dose of at least 30 mGy (mean 50 mGy) had around three times the risk of leukaemia.
The patients receiving a cumulative dose of 50-74 mGy (mean 60 mGy) had triple the risk of developing primary brain tumours. The authors say that, of every 10 000 people between the ages of 0-20 years receiving 10 mGy from a CT scan, there would be about one expected excess leukaemia case, whereas there were would be one excess case of brain cancer for every 30,000 people.
Applying the dose estimates for one head CT scan before the age of 10 years, this would translate into approximately one excess case of leukaemia and one excess brain tumour per 10 000 patients in the decade after first exposure. The authors note that increased follow-up and analysis of other cancer types is needed to identify the total excess risk for all cancers associated with CT scans.
The authors note that, in the UK, the Ionising Radiation (Medical Exposure) Regulations mean that a CT scan should only be done when clinically justified. This might explain the relatively low levels of CT use in the UK compared with other countries that do not have such regulations.
According to the lead author Dr Pearce the immediate benefits of CT outweigh the potential long¬term risks in many settings and because of CT's diagnostic accuracy and speed of scanning, notably removing the need for anaesthesia and sedation in young patients, it will, and should, remain in widespread practice for the foreseeable future.
He argued that further refinements to allow reduction in CT doses should be a priority, not only for the radiology community, but also for manufacturers. Alternative diagnostic procedures that do not involve ionising radiation exposure, such as ultrasound and MRI [magnetic resonance imaging] might be appropriate in some clinical settings. Of utmost importance is that where CT is used, it is only used where fully justified from a clinical perspective.
"It's well known that radiation can cause cancer but there is an ongoing scientific debate about whether relatively low doses of radiation like those received from CT scans do increase cancer risks, and if so the magnitude of those risks. Ours is the first study to provide direct evidence of a link between exposure to radiation from CT in childhood and cancer risk and we were also able to quantify that risk." Dr Berrington de González a co-author added
In a linked comment, Dr Andrew J Einstein, New York Presbyterian Hospital and Columbia University Medical Center, New York, NY, USA, says: "This study should reduce the debates about whether risks from CT are real, but the specialty has anyway changed strikingly in the past decade, even while the risk debate continued. New CT scanners all now have dose-reductions options, and there is far more awareness among practitioners about the need to justify and optimise CT doses—an awareness that will surely be bolstered by Pearce and colleagues' study."
I am not sure that this comment applies to countries such as India.An AERB funded project on CT scan practices in Tamil Nadu revealed that 32 out of the 71 centres do not follow paediatric protocols. Evidently the children undergoing CT exams in these clinics are receiving more doses.
The risk from this practice may be small. But there is no reason why those children should receive unwanted doses. Parents may ask the technologist whether the x-ray centre is following pediatric protocols or not . If they are not ,parents may insist on getting reference to centres where the protocols are followed.
There is some thing unique about this study. The risk estimate in this instance is directly derived. Dozens of such studies are going on all over the world. Normally, the researchers estimated the cancer risks from CT on the basis of risk estimates derived from A-bomb survivors. There were justifiable criticism against this approach.
You can access the paper at:
This paper is published Online First by The Lancet on 7 June 2012.
The absolute risk of these cancers occurring after CT is small but there is sufficient reason to keep the radiation doses from CT scans as low as possible.Dr Mark Pearce and Professor Sir Alan Craft, Newcastle University, UK; Professor Louise Parker, Dalhousie University, Halifax, NS, Canada; Dr Amy Berrington de González, National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD, USA, and colleagues conlude that if appropriate, alternative procedures, that do not use ionising radiation, should be considered. The study represents the culmination of almost two decades of research in this area, and is jointly funded by the UK Department of Health and NCI/NIH.
CT imaging is a unique medical radiation procedure. Use of this technology has increased rapidly in the USA and elsewhere, especially in the past decade. However, potential cancer risks exist due to the ionising radiation used in CT scans, especially in children who are more radiosensitive than adults.
In this retrospective study, the authors examined the records of close to 180,000 patients who underwent a CT scan between 1985 and 2002. It includes the records from the radiology departments of some 70% of the UK's hospitals. They extracted the number and types of CT scan from the records and estimated the dose absorbed in milli-Grays (mGy) by the brain and bone marrow in patients for each scan.
Then they linked the data to cancer incidence and mortality reports in the UK National Health Service Registry between 1985 and 2008. From this, they calculated excess incidence of leukaemia and brain tumours. The dose of radiation received by the brain and bone marrow varies by age, and body part scanned.
A total of 74 from 178 604 patients were diagnosed with leukaemia and 135 of 176 587 were diagnosed with brain cancer. The authors calculated that the relative risk of leukaemia increased by 0.036 per extra mGy received, whilst for brain tumours this increased risk was 0.023. Compared with patients who received a dose of less than 5 mGy, patients who received a cumulative dose of at least 30 mGy (mean 50 mGy) had around three times the risk of leukaemia.
The patients receiving a cumulative dose of 50-74 mGy (mean 60 mGy) had triple the risk of developing primary brain tumours. The authors say that, of every 10 000 people between the ages of 0-20 years receiving 10 mGy from a CT scan, there would be about one expected excess leukaemia case, whereas there were would be one excess case of brain cancer for every 30,000 people.
Applying the dose estimates for one head CT scan before the age of 10 years, this would translate into approximately one excess case of leukaemia and one excess brain tumour per 10 000 patients in the decade after first exposure. The authors note that increased follow-up and analysis of other cancer types is needed to identify the total excess risk for all cancers associated with CT scans.
The authors note that, in the UK, the Ionising Radiation (Medical Exposure) Regulations mean that a CT scan should only be done when clinically justified. This might explain the relatively low levels of CT use in the UK compared with other countries that do not have such regulations.
According to the lead author Dr Pearce the immediate benefits of CT outweigh the potential long¬term risks in many settings and because of CT's diagnostic accuracy and speed of scanning, notably removing the need for anaesthesia and sedation in young patients, it will, and should, remain in widespread practice for the foreseeable future.
He argued that further refinements to allow reduction in CT doses should be a priority, not only for the radiology community, but also for manufacturers. Alternative diagnostic procedures that do not involve ionising radiation exposure, such as ultrasound and MRI [magnetic resonance imaging] might be appropriate in some clinical settings. Of utmost importance is that where CT is used, it is only used where fully justified from a clinical perspective.
"It's well known that radiation can cause cancer but there is an ongoing scientific debate about whether relatively low doses of radiation like those received from CT scans do increase cancer risks, and if so the magnitude of those risks. Ours is the first study to provide direct evidence of a link between exposure to radiation from CT in childhood and cancer risk and we were also able to quantify that risk." Dr Berrington de González a co-author added
In a linked comment, Dr Andrew J Einstein, New York Presbyterian Hospital and Columbia University Medical Center, New York, NY, USA, says: "This study should reduce the debates about whether risks from CT are real, but the specialty has anyway changed strikingly in the past decade, even while the risk debate continued. New CT scanners all now have dose-reductions options, and there is far more awareness among practitioners about the need to justify and optimise CT doses—an awareness that will surely be bolstered by Pearce and colleagues' study."
I am not sure that this comment applies to countries such as India.An AERB funded project on CT scan practices in Tamil Nadu revealed that 32 out of the 71 centres do not follow paediatric protocols. Evidently the children undergoing CT exams in these clinics are receiving more doses.
The risk from this practice may be small. But there is no reason why those children should receive unwanted doses. Parents may ask the technologist whether the x-ray centre is following pediatric protocols or not . If they are not ,parents may insist on getting reference to centres where the protocols are followed.
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