CT radiation risks coming into clearer focus
BMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f3102 (Published 21 May 2013) Cite this as: BMJ 2013;346:f3102
All rapid responses
Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles or when it is brought to our attention that a response spreads misinformation.
From March 2022, the word limit for rapid responses will be 600 words not including references and author details. We will no longer post responses that exceed this limit.
The word limit for letters selected from posted responses remains 300 words.
Careful examination of the diagnostic benefit vs the hazards of any investigation is essential. In respect of CT imaging the data from Matthews et. al. are important and will give many clinicians pause for thought. Some would advocate a greater use of MR imaging in children, particularly the young (although neither Matthews et. al nor this editorial do so).
Because young children often need sedation or general anaesthesia to keep still for MRI this brings as yet unmeasured risks. Complications range from the common, such as behavioral changes and aspiration, to the rare and life threatening.
Until the hazards of alternatives are quantified changing to other diagnostic technologies cannot be recommended on safety grounds alone.
Competing interests: I anaesthetise children for MRI.
The research Article in the British Medical Journal of 1st June 2013 has increased the awareness of the risks of ionising radiation and its risk of developing cancer later on in life. The demand for imaging especially computed tomography has increased vastly over the last 20 years. An estimated 30% of computed tomography is unnecessary. An average effective dose of radiation from a CT brain is 2.mSv and it is equivalent to that of 100 radiographs and 304 days of natural background radiation (1).
One in 800 women aged 40 will develop cancer from a single CT brain scan with some form CT scanning posing a one in 80 risks of causing cancer (2). Over 300 scans need to be done for one patient to have a treatable abnormality and 9% of incidental abnormalities will be found in these 300 scans. For every treatable tumour that can be found one new cancer will be caused (3)
Incidental and non-significant findings on images can cause unnecessary worry to both doctors and patients and will increase health care costs. The current trend towards the use of high resolution scanning will result in manufacturing morbidity and increase health care cost by uncovering ’abnormal’ imaging findings of no clinical significance. Clinicians should be aware that doing imaging to reassure patients may be doing more harm than good.
1. British Medical journal March 2011.
2. Smith-Bindman. New England Journal of Medicine 2010.
3. British Journal of General practice March 2011.
Competing interests: No competing interests
The radiation risks of x-rays also need to be brought into sharper focus: my GP recently requested an x-ray of both thoracic and lumbar spine at the local cottage hospital. This showed a fracture at C12. Unconvinced that the site of my pain and the reported fracture site matched, and having in mind past experience when a full back scan had been ordered but only partly carried out, I asked for a copy of the radiological report. This made no mention of thoracic spine but only reported lumbar spine.
When I mentioned this to my GP she said 'Yes, I noticed that'. She then ordered another x-ray. While waiting about 20 minutes beyond my appointment time, I overheard a conversation between the (lone) radiographer and someone who had come to discuss delivery of a new x-ray machine and learned that the present one was about 30 years old.
I already had worries that the two x-rays might overlap, delivering a double dose to part of my spine. Now I wondered about the total radiation dose from this ancient machine, especially since I had previously received full pelvic radiotherapy for anal cancer and also radiotherapy for breast cancer.
I asked for copies of pictures of the x-rays, hoping to see if there was an overlap, and was told this would cost £50.00, but it was doubtful if I could have them as they had been sent to another hospital, and it was not even known if my GP could access them as their computers might not be compatible. However, if my GP referred me to a consultant they would be able to provide them free.
Incidentally, the second x-ray showed another fracture at C11. Yet another reason why patients need copies of all medical notes and investigations.
Competing interests: No competing interests
The editorial fails to mention that most pediatric and much adult CT can and should be replaced by MR. In Australia MR is rationed by deliberate government policy. GPs cannot order MR studies, with few exceptions. Waiting lists for a funded MR scan are typically a month or more. This policy is the major factor behind the continuing quite unnecessary radiation exposure inherent in CT.
Competing interests: No competing interests
Re: CT radiation risks coming into clearer focus
Dear Sir,
Please will you consider the letter below for publication in the BMJ. I believe that the risks of spreading non proven concepts of CT scans causing cancer, albeit in small numbers, is dangerous. Children are denied clinically helpful imaging because frightened parents and pediatricians may refuse the study because of what journals publish and the media rejoice in reporting.
Cancer risk from low dose CT scans – not proven.
You have recently published an Editorial accepting that low dose radiation from CT scans does increase the risk of cancer in children. This is based to two very large population studies. The UK study by Pearce et.al. was published last year in the Lancet and the Australian study was published earlier this year in the BMJ.
The articles have real problems. Both articles claim a cause and effect relationship between CT radiation and increased cancer risk. Neither article has shown this. As was taught by Doll and Hill in their identification of cancer risk from smoking, in order to prove cause and effect, one must show not only a statistical relationship but also a decrease in the cancer with removal of the cause. Neither the Lancet nor the BMJ article has done this.
In addition both articles have no real patient specific data. Their statistical analysis may appear extremely impressive, but the conclusions can only be made if the input data is valid and accurate. All their calculations of dose received by patients are crude approximations based on a large cascade of assumptions and estimations. I would argue that this method of looking at radiation dose may have some value in tracking population exposure over long periods of time. It is not accurate enough for specific scientific studies trying to prove that low dose CT in children increase the incidence of cancer.
Yours Sincerely
Mervyn Cohen
Competing interests: No competing interests