Radiation Exposure 1980 to 2006

Size: px

Start display at page:

Download "Radiation Exposure 1980 to 2006"

Clyde Richardson
6 years ago
Views:

1 Radiation Exposure 1980 to 2006 Background 3-6 msv/yr Natural (85% 45%) Radon Cosmic Rays Air travel Living at Altitude Man-made (15% 55%) Medical Imaging** mgy Radiation Therapy cgy

2 Radiation Whole Body Equivalent Damage (resultant biological effect) REM, Sievert Energy x quality factor (Q) or radiation weighting factor (RWF) Organ specific Different particles e.g. 1 for beta, gamma, x-rays Effective Dose Equivalent damage (Sv) x Tissue weighted factor (TWF) ICRP 2007

3 CT doses CT Dose Index Radiation dose per slice Volume adjusted Pitch and attenuation toward middle Dose Length Product (DLP) CTDI vol x scan length = DLP mgy-cm Conversion coefficients Risk assessment DLP x E DLP 1050 x.0023 = Sv or 2.3 msv

4 CT Trauma Neuro (head, neck)

5 CT Dose reduction Automated Tube Current modulation (automated exposure control) Longitudinal (z-axis) and Angular (xy)

6 CT Dose Reduction Partial Scan Shielding (Bismuth over breasts) Z over-ranging/overlap Increased noise tolerance Data reconstruction

7 Fetal/Pediatric Risk Communication Will this X-ray harm my baby? <50 mgy (5 RAD) will not injury fetus/child mgy (5-50 RAD) will increase risk Per/post implantation Organogenesis (2-7 wks) Early development (8-15 wks) No adverse health effects >15 wks Fetus: LD 50 1 Gy, LD Gy

8 Adult Risk Communication 40 yo receives 100 msv dose Signal to noise ratio! Impact at age 75 yo Excess relative risk 0.04% Dose and Dose Rate Effectiveness Factor Uncertainty factor 2-3 Increased relative risk 22.8% (natural) to % (excess) Absolute risk Better estimate 5%/Sv for low level exposure

9 Extrapolation Verdun F R et al. Radiographics 2008;28: by Radiological Society of North America

10 Biological repair mechanisms Stimulation of superoxide dismutase (SOD) Increased DNA repair Induced apoptosis Immune response (signaling) Cell cycle progression Gene expression changes Feinendegen LE Br J Radiol 2005

12 Medical Imaging Radiation Understanding and Communicating Risks

13 Radiation Particles and Waves Ionizing and Non-ionizing Source Absorbed Energy (amount of radiation/unit mass) RAD, Gray (joules per kilogram)

14 Radiation Whole Body Equivalent Damage (resultant biological effect) REM, Sievert Energy x quality factor (Q) or radiation weighting factor (RWF) Organ specific Different particles e.g. 1 for beta, gamma, x-rays Effective Dose Equivalent damage (Sv) x Tissue weighted factor (TWF) ICRP 2007

16 X-rays A narrow portion of the EMS Ionizing radiation Electrons (photons) emitted from X-ray tubes Energy: kev

time (sec) 60-140 mas Tube potential (kev) discrete 80-140 kevp Noise

18 CT Anatomy Hounsfield Nobel prize 1979 Current generation 64 slice (0.625 mm/slice) Dose reduction strategies Tube current (ma) and Exposure time (sec) mas Tube potential (kev) discrete kevp Noise index parameter Pitch Range of scan (body part) # acquisition phases

19 CT Dose reduction Automated Tube Current modulation (automated exposure control) Longitudinal (z-axis) and Angular (xy)

20 CT Dose Reduction Partial Scan Shielding (Bismuth over breasts) Z over-ranging/overlap Increased noise tolerance Data reconstruction

21 CT doses CT Dose Index Radiation dose per slice Volume adjusted Pitch and attenuation toward middle Dose Length Product (DLP) CTDI vol x scan length = DLP mgy-cm Conversion coefficients Risk assessment DLP x E DLP 1050 x.0023 = Sv or 2.3 msv

22 CT Abd/Pelvis Dose Report

23 CT Trauma Neuro (head, neck)

24 CT scan dose variability FDA requires CT makers to record dosing (phantoms) No guidelines for monitoring and regulating CT during clinical applications 13x dose range amongst institutions Pt size and area scanned (tech and protocol) Phases (protocol) Smith-Bindham R Ach Int Med 2009

25 Medical Imaging US 2007 >70 M CT scans 75% hospital-based 24.5 M abd/pelvis (10 msv) 21.5 M head (2 msv) 11 M chest (7 msv) 4 M children (7%)

26 Radiation Exposure 1980 to 2006 Background 3-6 msv/yr Natural (85% 45%) Radon Cosmic Rays Air travel Living at Altitude Man-made (15% 55%) Medical Imaging** mgy Radiation Therapy cgy

27 Regulatory Risk Goal Carcinogen ALARA or ALARP As low as reasonably achievable (practicable)

28 Ionizing Radiation Risk Deterministic (< 2 Gy) Immediate burns, cell and tissue death Gonadal and fetal injury/death Stochastic (< 1 Gy) Future outcome, probabilistic Tumor, cancer

29 Applying population statistics to individuals

30 Fetal/Pediatric Risk Communication Will this X-ray harm my baby? <50 mgy (5 RAD) will not injury fetus/child mgy (5-50 RAD) will increase risk Per/post implantation Organogenesis (2-7 wks) Early development (8-15 wks) No adverse health effects >15 wks Fetus: LD 50 1 Gy, LD Gy

33 Prenatal risks Will this x-ray increase my baby/child risk of developing cancer? Oxford Survey of Childhood Cancers (OSCC) CA RR (0.194 ERR/film) NRPB Excess relative risk (ERR) 0.038/mGy Absolute risk in utero radiation 6%/Gy (2.5%/Gy leukemia) childhood CA

34 Estimated Lifetime Attributable Risk for Cancer from Prenatal Exposure Radiation Dose Childhood CA Lifetime CA Background 0.3% 38% 0-5 RAD 0.3%-1% 38-40% 5-50 RAD 1-6% 40-55% >50 RAD >6% >55%

35 To communicated these facts If a pregnant pt has an abd CT The absolute increase in childhood cancer of fetus 8 mgy 6%/Gy or 6% x.008 Gy 0.05% or 1 in 2000 but range of up to 1 in 20,000

37 Adult Risk Communication 40 yo receives 100 msv dose Signal to noise ratio! Impact at age 75 yo Excess relative risk 0.04% Dose and Dose Rate Effectiveness Factor Uncertainty factor 2-3 Increased relative risk 22.8% (natural) to % (excess) Absolute risk Better estimate 5%/Sv for low level exposure

Adult CA risk estimates Berrington de Gonzalez et al 2009 57 M CT scans (exclude end of life, CA scans) 1 death per 2000

38 Adult CA risk estimates Berrington de Gonzalez et al M CT scans (exclude end of life, CA scans) 1 death per 2000 scans (BIER VII LNT model) 10 msv per scan Risk of cancer 5%/Sv 29,000 future excess CA 14,500 CA deaths (50% mortality)

39 Adult Risk Communication X-rays <0.1-1 msv Risk 10-5 to -6 Negligible to minimal Analogous to risk of death from 4500 mile flight CT 1-10 msv Risk 10-4 Very low Analogous to risk of death from 200 mile car Multiple CT 10 to > 100 msv Risk 10-3 to -2 or Low to moderate Adults LD Gy, LD Gy

40 Why none of this makes sense Extrapolating from high dose exposures causes uncertainty Current dosing models do not consider basic biological principles Multiplying very small incremental risks with 2x-3x error margins times large population leads to enormous range of values Since the introduction of CT scan dose reduction methods radiation 16-90%

41 Risk Assessment Extrapolation Life Span Study (LSS) Report ,572 A-bomb survivors >9000 solid cancers Sex, age specific excess risk increased 500 msv to 2000 msv Pierce DA and Preston DL 2000 Low-dose cohort 5 msv to 200 msv 35, solid cancers based upon LNT model 137 excess CA Threshold below 100 msv

42 Risk Assessment Extrapolation Nuclear Industry workers 15 country 407,391 workers Avg cumulative dose 20 msv (90% <50 msv) All cancer mortality RR 1.10 Lung CA 1.19 at 100 msv (not controlled for smoking)

43 Extrapolation Verdun F R et al. Radiographics 2008;28: by Radiological Society of North America

44 Ionizing Radiation Energy to generate -OH groups Reactive oxygen species (ROS) Base damage and strand breaks Misrepair Point mutations Chromosomal abnormalities Gene fusion Eventual tumor/cancer growth

45 Biological repair mechanisms Stimulation of superoxide dismutase (SOD) Increased DNA repair Induced apoptosis Immune response (signaling) Cell cycle progression Gene expression changes Feinendegen LE Br J Radiol 2005

46 Hormesis Adaptive response Conditioning

49 Bibliography Pediatrics Ratnapalan S, Bentur Y, Koren G, Doctor, will that x- ray harm my unborn child, CMAJ, 179(2): , Frush DP, Radiation CT and Children: The Simple Answer is It s Complicated, Radiol, 252(1): 4-6, Brody AS, Frush DP, Huda W et al., Radiation Risk to Children From CT, Pediatr 120(3): , Doll R, Wakeford R, Risk of Childhood Cancer from Fetal Radiation, Br J Radiol, 70: , 1997.

50 Bibliography Dose response Tubiana M, Feinendegen LE, Yang C et al., The Linear No-Threshold Relationship is Inconsistent with Radiation Biology Experimental Data, Radiol, 251(1): 13-22, 2009.

51 Bibliography CT Technology Singh S, Kaira MK, Thrall JH et al., CT Radiation Dose Reduction by Modifying Primary Factors, J Am Coll Radiol, 2: , Strauss KJ, Goske MJ, Kaste SC et al., Image Gently: 10 steps you can take to Optimize Image Quality and lower CT dose for Pediatric Patients, J Am Coll Radiol, 194(4): , Gunn MLD, Kohr JR, State of the Art: technologies fpr CT dose reduction, Emerg Radiol, 17: , 2009.

52 Bibliography Fayngersh V, Passero M, Estimating Radiation Risk from CT, Lung, 187: , Brenner DJ, Hall EJ, CT An Increasing Source of Radiation Exposure, NEJM, 357(22): , Verdun FR, Bochud F, Gudinchet F et al., Radiation Risk: What You Should Tell Your Patient, Radiograp, 28(7): , Berrington de Gonzalez A, Mahesh M, Kim K et al., Projected Cancer Risks from CT Scans Performed in the US in 2007, Arch Int Med, 169(22): , Smith-Bindman R, Lipson J, Marcus R et al., Radiation Dose Associated with Common CT Exams and Lifetime Attributable Risk of Cancer, Arch Int Med, 169(22): , 2009.

Radiation Dose in Pediatric Imaging

Radiation Dose in Pediatric Imaging A Brief History of Radiology Dose: Why Does It Matter? Measuring Exposure and Dose Deterministic Effects Stochastic Effects Common Exams: What is the Risk? Reducing