Estimations of radiation-induced risks from low doses and how to communicate these risks Sören Mattsson Medical Radiation Physics, Lund University and Skåne University Hospital Malmö, Sweden Medical Physics in the Baltic States 11th Conference & Workshop 10-12 October 2013 Malmö Illustration of the dose–response relationship for radiationinduced carcinogenesis in humans. (Hall, 2004, 2009) but … Extrapolation models for estimating radiation risk at low dose. Image shows 4 models: linear, no threshold (solid black line); linear, with threshold (dashed black line); super linear (blue line); and hormetic (red line) (NCRP, 2008) Hall, 2009 How the concern regarding exposure to ionising radiation has changed from heritable effects to carcinogenesis Radiation-induced cancer: • • • • Scientific basis for current radiation protection. Epidemiology Survivors of Hiroshima and Nagasaki Patients in health care (radiation therapy, repeated diagnostic radiology, CT investigations of children) Occupationally exposed persons Environmental exposures Animal experiments Cell research Epidemiology: All cancers – All ages Deviation of cancer mortality from the average (0/00) in 1996-2005 (SEER-USA) and radiation effects (ICRP) Hiroshima/Nagasaki 1945 86 572 persons Solid cancers Solid cancers Solid cancers Leukaemia Non-cancer (cariovascular disease, cognital effects, diabetes) Patients in healthcare • • • • • • External radiotherapy Haemangioma treatment with 226Ra Chest radiograph at TBC - dose to the breast Thyroid diagnostics with 131I In utero diagnostic x-rays Children who were examined with CT Occupationally exposed persons Medical staff Chernobyl emergency and recovery workers Participants in nuclear weapons tests Workers in the nuclear weapons and power industries • Underground miners • Radium dial painters • • • • Environmental exposures • Radon in homes • Chernobyl contaminated areas • Mayak, Techa river, Kyshtym Cancer risk • UNSCEAR, lethal solid cancer: 11% Sv –1 (men 9%, women 13%) • Reduce with a factor of 2 at low doses or dose-rates, which means a risk of about 5% Sv–1 (uncertainty interval: 1%-9%) • Risk for fatal leukemia: 1% at 1 Sv; 0,05% at 0,1 Sv Risk of dying from radiation-induced cancer later in life (population average) according to ICRP 10% per Sv ? 5% per Sv (1-9%) Equivalent dose, Sv Effective dose, Sv Base for information about radiation risks of lowdose radiation exposure - Health effects of low dose radiation exposure (5, 10, 20 mSv)? - Results from epidemiology in general - Results from epidemiology related to specific age groups - Biophysical arguments - The linear non-threshold (LNT) - model What happens at lower doses of radiation? Pelvimetry or obstetric abdominal examination There are data to support the hypothesis that there is a risk also at lower doses - Increased risk of cancer during childhood after X-ray in utero with 6-10 mSv (mean 1 electron / cell) - Biophysical argument If the dose is reduced, we get fewer electron tracks and fewer hits of cells. The cells that are hit suffer the same type of injury and the same biological process is initiated. - Increased risk of cancer after CTinvestigations during childhood. Average absorbed dose: 6 mSv 80 kV x-rays Equivalent to about 1 electron per nucleus Alice Stewart (1906-2002) The base of the biophysical argument for a linear relationship between dose and effect at low doses: Track structure at 1000, 10 and 1 mSv Risk varies with age Risk of dying from cancer in the rest of life (LNT-model) Mean for population 5% per 1 000 mSv 0,5% per 100 mSv 0,05% per 10 mSv 0,005% per 1 mSv Foetus, newborn 15% per 1 000 mSv 1.5% per 100 mSv 0.15% per 10 mSv 0.015% per 1 mSv Compare with the "natural" risk of dying from cancer: about 22% Remaining questions • Cancer The effect of low doses and dose-rates The effect of different types of radiation Extrapolations over time and between countries The importance of factors that may modify the risk Age Sex Genetically determined differences in radiosensitivity Environmental factors • Non-cancer effects Cardiovascular effects at low doses and dose rates Cognitive effects Diabetes Communication about radiation risks The respect and fear of radioactivity and radiation is very deep. In other contects the risks have been/still are neglected. Communication of radiological risks is not an easy task. Different in medicine and health-care than in the society after an accident . Some leading principles for all information 1. Transparency, openness. Tell the truth 2. Ask whether you are being understood 3. The listener must thrust on you 4. Initiative and speed 5. Quality Transparency, openness. Tell the truth. “Never underestimate people's talents, but do not overestimate their knowledge”. Take each question seriously-It is a chance to teach. Communicate therefore, openly and clearly. The listener must thrust you Requires transparency. Avoid ”double messages”. No danger Dagens Nyheter 2/5 1986 It is also important how to convey the information Example: Activity levels in food. It is perceived very differently if you say that the limit for Cs-137 in foodstuff is 300 Bq/kg or you say that you have to eat 75 000 Bq to get a dose of 1 mSv. As it was perceived, 300 Bq/kg was by many considered as a toxic limit. Concentration (Bq/kg)- and doserate (mSv/hr) values that are supposed to be tolerated for a long time will be perceived as absolute limits. Base for information about radiation risks of low-dose radiation exposure - Quantities and units: Use only Bq and mSv for activity and ”dose” respectively http://www.imagewisely.org/Imaging-Professionals/Medical-Physicists/Articles/Howto-Understand-and-Communicate-Radiation-Risk Comparison of dose contributions with the natural effective dose What to tell the radiologist and the general practitioner Any added risk, however small, is not acceptable if it does not benefit the patient. Justification and optimization of a procedure are absolutely essential. Diagnostic reference levels should be used to reduce variations from one center to another and to promote optimal dose indicator ranges for medical imaging protocols. The basic principles of radiation protection need to be respected to help counteract the unjustified explosion in the number of procedures now being performed. … thank you for listening [email protected] Telephone +46 40 331374 Verdun et al., 2008 Example of a risk comparison Of 2 500 10 year old children, 550 will die from cancer for reasons other than man-made sources of ionizing radiation A 10 year old who gets 4 mSv effective dose (Ex: CT abdomen, bone scan). Risk of dying from radiation-induced cancer in the rest of life: 10% per Sv. 0.004 Sv x 10% per Sv gives a risk of 0.0004 or 1 per 2 500 (the star in the picture).