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RADIATION DOSE AND RISK IN CT Radiation Dose and Radiation Risk OBJECTIVE Explain Radiation dose parameters (for CT) and associated risk of radiation exposure: Radiation Dose and CT specific CTDIvol: milligray (mGy) Radiation Risk DoseLength product (mGy*cm) general whole body dose (mSv) Dominik Fleischmann (relates to risk) Department of Radiology Stanford University RADIATION DOSE AND RISK IN CT Risk of Radiation Exposure Internatonal commision on radiological protection – IRCP estimates • Deterministic (high dose range) 250 – 500 mSv blood changes >4000 mSv 50% probability of death Radiation Risk (mSv) • Stochastic (low dose range) Risk of fatal cancer (~5% per 1000mSv) Risk of non-fatal cancer (1.2% per 1000mSv) general whole body dose (mSv) (relates to risk) ~ 0.01 % /mSv Cancer risk (incl.non-fatal) ~ 0.005 % /mSvfatal Cancer risk Deterministic Deterministic effects of high effects of high radiation dose .. radiation dose .. California Bill SB 1237 (signed Sept 2010) 1 Risk of Radiation Exposure Estimated number of cancers from 100mSv Internatonal commision on radiological exposure for 100,000 persons protection – IRCP estimates Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VI report Berrington de Gonzalez et al., Arch Intern Med. 2009 • Deterministic (high dose range) All solid cancer Leukemia 250 – 500 mSv blood changes males females males females >4000 mSv 50% probability of death Excess cases 800 1300 100 70 (including non-fatal) (400-1600) (600-2500 (30-300) (20-250) • Stochastic (low dose range) cases in the absence 45,500 36,900 830 590 <100 mSv: definition of 'low exposure' of exposure Risk of non-fatal cancer Excess deaths~1000 from cancers410 / 100mSv /610 100,000 persons70 = 50 exposure to 100 mSv (200-830) (300-1200) (20-220) (10-190) Risk of fatal cancer ~10 cancers / mSv / 1,000 persons = deaths in the absence~1 cancer 22.100 / mSv / 10,000 17.500 persons 710 = .. 530 of exposure not well known, linear, no threshold dose-effect relationship? ~ 0.01% / mSv Cancer risk (incl. non fatal) ~ 0.005% / mSv fatal Cancer Estimated Risks of Fatal Malignancy of Death from MDCT Radiation Dose Radiation Exposure and Lifetime Odds of Dying as a Typical effective dose values Result of Selected Activities of Everyday Life (per 100 Individuals) C. McCollough, MDCT Course 2003 San Francisco • Head CT 1-2 mSv • 1 mSv (calcium score) 0.005 • Chest CT 5-8 mSv • 10mSv (coronary CT, cath, ..) 0.05 Abdomen CT 5-10 mSv • • 50mSv (yr radiation worker allowance) 0.25 • Pelvis CT 3-4 mSv • Abd-Pelv CT 8-15 mSv • 100mSv (definition of 'low exposure') 0.5 • NATURAL fatal cancer 21.2 • Chest x-ray 0.02 mSv • Abdomen x-ray 0.07 mSv • passive smoking 0.4-1.0 • radon in home (US average) 0.3 • Average U.S background radiation ~ 3.6 mSv • Motor vehicle accident 1.9 ~ 0.01% / mSv Cancer risk (incl. non fatal) ~ 0.005% / mSv fatal Cancer ~ 0.005% / mSv fatal Cancer Gerber et al. Circulation 2009 Computed Tomography (CT) Computed Tomography (CT) in the United States in 2007 in the United States in 2007 • approx. 70 million scans / year • approx. 70 million scans / year (threefold increase of CT since 1993) (threefold increase of CT since 1993) Overall, we estimated that approx. 29 000 * (95% UL, 15 000-45 000) future cancers could be related to CT scans performed in '07 in US. The largest contributions were from scans of - abdomen and pelvis (n = 14 000) - chest (n=4100), - head (n=4000), - chest CT angiography (n=2700). (*2% of ~1.4 m cancers diagnosed annually in US) Berrington de Gonzalez et al., Arch Intern Med. 2009 Berrington de Gonzalez et al., Arch Intern Med. 2009 2 Scan Type Scans (mio) Percent MDCT Radiation Dose Head 21.5 30 Chest 11 15 Typical effective dose values Cervical spine 1.8 2.5 C. McCollough, MDCT Course 2003 San Francisco Thoracic spine 0.4 0.6 • Head CT 1-2 mSv Lumbar spine 2.5 3.5 • Chest CT 5-8 mSv CT dose of 15mSv Abdomen/pelvis 24.2 34 Abdomen CT 5-10 mSv CTA chest 2.6 3.6 • ~ 750 chest x-rays CTA abdomen 0.9 1.3 • Pelvis CT 3-4 mSv ~ 4 years backgr. ormed in the U.S. in 2007 CTA pelvis 0.5 0.7 • Abd-Pelv CT 8-15 mSv CTA head 0.7 1.0 ~ 0.15% cancer . other cardiac 0.5 0.7 • Chest x-ray 0.02 mSv (incl. non-fatal) Whole body 0.3 0.4 • Abdomen x-ray 0.07 mSv Colonography 0.2 0.3 calcium scoring 0.7 1.0 Other 45.6 Average U.S background radiation ~ 3.6 mSv Berrington de Gonzalez et al., Arch Intern Med. 2009 • Total 71.7 100.0 Number of CT Scans Perf nationalcommercialMedicare, and Estimated using IMV,7 insurance database MDCT Radiation Dose MDCT Radiation Dose Calculated radiation-induced Typical effective dose values Risk of dying from cancer per mSv. C. McCollough, MDCT Course 2003 San Francisco • Head CT 1-2 mSv • Child (0-10y)Estimates, 14 / 100 extrapolated 000 from Chest CT 5-8 mSv Adolescent (10-20y) accidental10 / 100 or 000occupatonal • • whole-body exposure to high • Abdomen CT 5-10 mSv • Adult (20-30y) doses7.5 /and 100 dose-rates. 000 Risk • Pelvis CT 3-4 mSv • Adult (30-40y) cannot3.5 / yet100 be 000 statistically • Abd-Pelv CT 8-15 mSv • Adult (60) proven2.0 / for100 an 000 effective dose • Adult (80) below1.0 /20mSv. 100 000 • Chest 5-8 mSv (12-18 mGy) • Average 5.0 / 100 000 0.005% / mSv • Low-dose Chest 2-5 mSv (5-12 mGy) • HR-CT 1.2-2.5 mSv (3-5 mGy) • Natural risk 30 000.0 / 100 000 • Average U.S background radiation ~ 3.6 mSv ~ 0.01% / mSv Cancer risk (incl. non-fatal) IRCP publication 60 The Lancet, June 2012 The Lancet, June 2012 The Interpretation .. cumulative doses of about 50 mGy might almost triple the risk of leukaemia and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: in the 10 years after the first scan for patients younger than 10 years, one excess case of leukaemia and one excess case of brain tumour per 10 000 head CT scans is estimated to occur. 3 MDCT Radiation Dose Calculated radiation-induced Risk of dying from cancer per mSv. • Child (0-10y) 14 / 100 000 The Lancet, June 2012 The • Adolescent (10-20y) 10 / 100 000 • Adult (20-30y) 7.5 / 100 000 • Adult (30-40y) 3.5 / 100 000 • Adult (60) 2.0 / 100 000 • Adult (80) 1.0 / 100 000 Interpretation .. cumulative doses of about 50 mGy might almost triple the risk of leukaemia • Average 5.0 / 100 000 0.005% / mSv and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: Natural risk 30 000.0 / 100 000 in the 10 years after the first scan for patients younger than 10 years, one excess • case of leukaemia and one excess case of brain tumour per 10 000 head CT scans is estimated to occur. ~ 0.01% / mSv Cancer risk (incl. non-fatal) IRCP publication 60 RADIATION DOSE AND RISK IN CT Radiation Risk: Summary • very difficult estimate true effective dose (mSv) from CT exposure parameters (CTDI, DPL) • Radiation has deterministic effects at high doses (>250mSv), • CT doses are in the low dose range (<100mSv), CT specific CTDIvol: milligray (mGy) typically 1–50 mSv, which has stochastic effects (i.e. cancer, on population basis), with wide error DoseLength product (mGy*cm) margins of estimates ~ 0.01% / mSv Cancer risk (incl. non fatal) (CT) ~ 0.005% / mSv fatal Cancer Radiation Dose • prudent to reduce dose ALARA (as low as reasonably achievable) Radiation Dose in Computed Tomography Instrumentation for measurement of radiation OBJECTIVE exposure in computed tomography CTDI: CT Dose Index: Explain risk of radiation exposure and Radiation dose parameters: general milli Sievert [mSv] (whole body) CT specific CTDIvol: milligray (mGy) 2003;107:917-922 Circulation L. et al. R. Morin, DoseLength product (mGy*cm) CTDIw = (2*CTDIperiphery + CTDIcenter)/3 CTDIvol = CTDIw / pitch 4 CTDI (CT Dose Index) Not so Intuitive Concept … Dose Quantities in CT • Phantom size gives different CTDI for same scanning parameters: large phantom – less dose ! CTDIvol (mGy) CT dose index local dose displayed 32cm 16cm measured in head or body phantom on the scanner 140 140 12 mGy STANDARDIZED on all scanners, and 120 120 console 100 8 mGy 100 all models … 80 80 60 60 40 40 20 20 0 0 … most important parameter to optimize • Large patients shield themselves, slim patients your scan protocols! more dose than CTDI suggests Dose Quantities in CT Scan Protocol Optimization start with review scanning protocols and optimizing CTDIvol (mGy) • patient positioning (centering) CT dose index local dose displayed • scanning range measured in head or body phantom on the • number of phases scanner appropriate use of automated exposure control console • • mAs • new dose reduction techniques (e.g. ASIR) • kVp summarized completely • cardiac: gating technique, low heart rate • gantry rotation time in CT Dose index (CTDI) • for each acquisition, look at the CTDI in milli-Gray (mGy) • pitch • COMPARE TO REFERENCE VALUES • filtration European guidelines on quality criteria for Computed Tomography – EUR 16262 European guidelines on quality criteria for Computed Tomography – EUR 16262 Table 3: Proposed reference dose values for routine CT Table 3: Proposed reference dose values for routine CT examinations on the basis of absorbed dose to air examinations on the basis of absorbed dose to air Examination Reference dose value Examination Reference dose value CTDI (mGy) DLP (mGy cm) CTDI (mGy) DLP (mGy cm) w upper limits (ACR)w Routine heada 60 1050 Routine heada 60 1050 Face and sinusesa 35 360 Face •andHead sinusesa 35 ~ 70 mGy 360 Vertebral traumab 70 460 Vertebral• Body
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