Radiation Risks from Medical Imaging: Busting the Myths
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Epidemiologic evidence and bench research demonstrate the truth about low radiation risk to patients.
By Dr. Akshay Baheti and Dr. Bhavin Jankharia.
The perceived risk of radiation from medical imaging remains a major source of concern in the minds of many radiologists, referring physicians, and patients alike, with many instances of patients avoiding indicated studies to avoid radiation. The reason for this is the perceived risk of developing cancer in the future.
The facts about radiation doses in medical imaging
The truth, which every stake-holder needs to understand, is that in fact both epidemiologic evidence and bench research demonstrate that there is no reason to worry about radiation in doses less than 50-100 mGy, which is essentially all of diagnostic radiation.
The epidemiologic data available to us for developing models of radiation risk is based on high radiation exposure (>100 mGy at the minimum), as in the 1945 nuclear blasts or the Chernobyl tragedy. However, the fact is that everyone gets exposed to certain amount of background radiation irrespective of where they live. This for example amounts to approximately 3 mGy annually in most of USA.
There are however places like Ramsar, Iran, which are exposed to as high as 260 mGy annual background radiation, without there being an increased incidence of cancer in people living there . This is so because the human body is equipped with repair mechanisms to handle the damage caused by low dose radiation, in the form of DNA and RNA repair and anti-oxidative stress mechanisms. Thus, normal individuals can take care of low dose radiation without developing cancer.
The same logic applies to diagnostic radiation. As per the American College of Radiology (ACR), a chest X-ray, a single-phase CT abdomen pelvis, and a PET/CT cause approximately 0.1 mGy, 10 mGy and 25 mGy exposure respectively, which can similarly be easily taken care of by the human body.  It is only in patients receiving radiation therapy for cancer that we use high-dose radiation which can overwhelm the body’s repair mechanisms, leading to an increased risk of cancer.
International scientific bodies weigh in on radiation doses in medical imaging
This fact is accepted by most international scientific bodies. The Health Physics Society, the American Association of Physicists in Medicine, and French Academy of Sciences and National Academy of Medicine, and the International Commission on Radiological Protection (ICRP) task group on Fukushima, amongst others, have clearly stated that there is no evidence that radiation <100 mGy causes increased cancer incidence or mortality [3-7]. In fact, the ICRP also states that at radiation doses <50 mGy, there is no risk even in pregnant patients, and that patients should consider aborting the fetus only if exposed to >100 mGy radiation . In fact, the International Atomic Energy Agency now states that the age-old 10-day rule should now be replaced by the 28-day rule, as the risk for fetuses is so minimal !
All the alarmist studies published in radiology literature are based on pure mathematical extrapolations from high radiation exposure data, and are not real-life figures. This practice of extrapolation has been denounced by various scientific agencies [5-7]. Unfortunately these articles have been widely shared in the media, and have created radiophobia in the minds of some patients and doctors.
Radiation dose and image quality equally important in medical imaging
There have been some benefits from the focus on radiation as well. The Image Gently initiative, which arose as a response to the growing radiophobia, has done excellent work on optimizing radiation doses to children. Companies have focused on developing low-dose algorithms which minimize radiation exposure to the patients. This fine work should and will continue to happen in the future as well.
However, one must remain guided by the principle of ALARA – ‘as low as reasonably achievable’ – for all patients. While we are stretching the limits of ‘as low as’ we can go, the ‘reasonably achievable’ component is also equally important. A patient refusing a CT or a PET/CT for an indicated study, or a pediatric study being poor quality and needing to be repeated due to lesser than optimal radiation dose being used, are both examples where ‘reasonableness’ goes for a toss.
It is our duty as doctors to strike a balance between the two, keeping the patient at the foremost of our concerns, rather than pandering to perceived risks and accommodating misperceptions about radiation risk. In any risk-benefit analysis for a patient needing an indicated imaging study, the benefit is always going to outweigh the perceived risk once we know these facts about low dose radiation. Thus, when a colleague or a patient asks us about the risk of radiation for a 25-year old or a 50-year old undergoing an X-ray or a CT, we should be confident in telling them to go ahead performing the study without worrying about carcinogenesis!
Editor’s note: The authors have written a ‘ready reckoner’ handbook dealing with radiation and imaging as well as other practical radiology issues such as contrast or pregnancy and imaging. It is available on Amazon and on Kindle
Dr. Akshay Baheti is Assistant Professor at Tata Memorial Hospital, Mumbai, one of Asia’s largest cancer hospitals. He also is affiliate faculty at the University of Washington Medical Center in Seattle, his alma mater. Apart from cancer imaging, he holds spreading awareness about non-interpretative skills such as radiation and contrast close to his heart.
Dr. Bhavin Jankharia is a consultant radiologist at Picture This in Mumbai India. He is a Past President of the Indian Radiology & Imaging Association. and Editor in Chief of the Indian Journal of Radiology & Imaging.
Understanding Radiology Exposure Indicators
Pediatric Diagnostic Reference Levels
- Siegel JA, Welsh JS. Does Imaging Technology Cause Cancer? Debunking the Linear No-Threshold Model of Radiation Carcinogenesis. Technol Cancer Res Treat 2016;15:249-56
- American College of Radiology. Radiation Dose to Adults from Common Imaging Examinations. Accessed on 22 Aug, 2019.
- Gonzalez AJ, Akashi M, Boice JD, Jr., et al. Radiological protection issues arising during and after the Fukushima nuclear reactor accident. J Radiol Prot 2013;33:497-571
- Tubiana M. Dose-effect relationship and estimation of the carcinogenic effects of low doses of ionizing radiation: the joint report of the Academie des Sciences (Paris) and of the Academie Nationale de Medecine. Int J Radiat Oncol Biol Phys 2005;63:317-9
- AAPM Position Statement on Radiation Risks from Medical Imaging Procedures
- Radiation risk in perspective. Position statement of the Health Physics Society. Accessed on 22 Aug, 2019
- On the risk to low doses (<100 mSv) of ionizing radiation during medical imaging procedures – IOMP policy statement. J Med Phys 2013;38:57-8
- Wang PI, Chong ST, Kielar AZ, et al. Imaging of pregnant and lactating patients: part 1, evidence-based review and recommendations. AJR Am J Roentgenol 2012;198:778-84
- Radiation protection of pregnant women in radiology. Accessed on 22 Aug, 2019
My 10 month old girl fell from bed so doctor advised ct scan. We done it and report came normal.
I have asked the radiologist about her radiation dose. However her dlp value was 476 and approx radiation was 3.2 mSv. i am Worried and stressed about her long term additional cancer risk. Pls tell me how much risk is there is future for her..?
Hello, I recommend that you discuss your concerns with your child’s doctor.