CT Safety: Realities and Myths of Radiation and Contrast Medium Adverse Events

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1 CT Safety: Realities and Myths of Radiation and Contrast Medium Adverse Events Dushyant Sahani MD Director of CT Associate Professor of Radiology MGH Disclosure Research Grant Support GE Healthcare BD Consultant, Bracco Diagnostics HARVARD MEDICAL SCHOOL Effective Dose Per Individual E (US) 6.2 msv Ubiquitous Background and other non-medical 3.2 msv Medical 3.0 msv Calculations based on data from NCRP Report 160 >72 million scans in USA in 2008 Dose with Various Exams Chest x-ray 0.01 msv CT of the chest 7 msv Abdomen-pelvis CT msv Dental x-ray msv Panoramic x-ray msv Dental CT 0.2 msv Head CT 2.0 msv Crew on an airline flight (annual) 2 msv Passenger on an airline flight 0.07 msv Emergency workers in Chernobyl >100mSv Background radiation in US (annual) 3.7 msv Berrington de González et al Arch Intern Med Smith-Bindman et al Arch Intern Med Do CT scans cause cancer? No study with definite link between a CT scan and later cancer development (Why) Definite link very difficult to prove Radiation induced cancer is identical to nonradiation induced cancer Cancer risk from radiation is higher < 30 yo Lifetime risk of death by cancer per million people exposed to 10 mgy Based on atomic bomb survivor data. Colon cancer Lung cancer Too many confounding factors: age, genetic/family history, diet, weight, smoking BEIR VII 2005 report AGE (yrs) 1

Lancet Study-June 2012 (Pearce M et al) 180,000 children in UK who get several CT scans (1985-2002) have a slightly higher chance of brain cancer

023%) increase in lifetime risk, once the overall rarity of brain tumors was taken into account Limitations of the Lancet study CT dose were

scan Average Effective Doses (msv) 50 40 30 msv 20 10 0 0.1 0.

Arch Intern Med 2009;169(22):2078-2086 50 Max/yr nuclear worker Lifetime risk of dying from Risk of dying Activity per 1000 people Cancer

9 Dental x-rays/panoramic 0 Abdomen CT 0.

2 Lancet Study-June 2012 (Pearce M et al) 180,000 children in UK who get several CT scans ( ) have a slightly higher chance of brain cancer and leukemia in later life Very small (0.023%) increase in lifetime risk, once the overall rarity of brain tumors was taken into account Limitations of the Lancet study CT dose were significantly higher than currently used (70-85% lower at MGH) Lack of control group for cancer risk in children of same age who did not have CT scan Average Effective Doses (msv) msv Phoenix 1 Avg background radiation 3 3 Denver CXR Mammo Head CT CTC Chest CT Abd CT AP CT Liver CT Smith-Bindman R. Arch Intern Med 2009;169(22): Max/yr nuclear worker Lifetime risk of dying from Risk of dying Activity per 1000 people Cancer (non-radiation induced) 228 Motor vehicle accident 12 Married to a smoker 10 US average radon level in home 3 Drowning 0.9 Dental x-rays/panoramic 0 Abdomen CT 0.05 Two Pillars of Radiation Dose Reduction Appropriate Utilization + Optimization of CT Protocols Splitting scan volumes increases dose Faster gantry rotation reduces radiation dose. However, noise is increased if the other factors are constant Scanning Parameters Off-centering increases dose 1. Localizer radiograph 2. Helical/axial 3. Tube current 4. Tube voltage 5. AEC 6. Rotation time Collimation, beam pitch, Automatic exposure control 7. Table feed/speed table speed 8. Pitch 9. Scan length 10. Detector configuration 11. Slice Thickness 12. Recon alg / kernel Extra images = 13. Phases (arterial/venous) Extra dose increases Decreasing 14. tissue kvp reduces dose and recon tech FBP/IRT contrast; increasing mas could reduce noise Strategies Commonsense Steps Leveraging Technology Innovative Solutions 2

3 MINIMIZE COVERAGE: Less is More Limit Scanning Area MINIMIZE COVERAGE Routine AP: hemidiaphragms to pubic symph Dose Reduction by 20% Top of diaphragm to lower border of ischium Top of L 1 to upper border of symphysis CTC (colon only) CTA (stent only) Renal/Adrenal (limited to anatomy) CTU: (kidneys to bladder only) Post-cystogram (bladder) Overlap Scanning: Extra Radiation Dose MINIMIZE COVERAGE 25% EXTRA DOSE Χ Renal/Adrenal Delayed phase Limiting Phases in CT Urography Triple phase CTU vs Split Bolus Unenhanced CT ml IV CM (370 mgi/ml) 250 ml saline drip infusion Wait minutes (Prone) ml IV 3 ml/s Scan at 100 sec delay Limiting the Phases: Renal Donor CT Dose Reduction by 60 70% Base scan only in patients less than 40 yrs of age if a stone is seen Split Bolus: 25 % Dose Reduction compared to Triple phase CTU kvp: 80 Scout image at 8 minutes for excretory phase 80 kvp 3

WL=0 WW=100 WL=0 WW=100 Patient Off centering Increases Dose and Noise

WW=100 Phantom scanned at different centering positions in CT gantry 60 mm

Collimation 6% Noise 22% 21% Surface dose 49% 18% Peripheral dose 41% Li et

decrease in ma = 50% dose reduction 140-120 kv = 40% dose reduction

IN Tube current Tube potential Gantry rotation time * Scan length Overlap

collimation *Provided other scanning factors are kept constant Indication

B C D CT dose 6.8 msv CT dose 2.2 msv 430 lbs 156 lbs CT dose 1.

5 sec 80kVp NI-25 2.5 mm 0.5 sec CT dose 1.06 msv 14.3 msv 7.3 msv 5.

4 WL=0 WW=100 WL=0 WW=100 Patient Off centering Increases Dose and Noise Parameters and Dose 0 mm 30 mm dose kvp 2 Tube potential Gantry center WL=0 WW=100 Phantom scanned at different centering positions in CT gantry 60 mm Patient CT Scanner dose mas Exposure time Tube Current Beam Quality Collimation 6% Noise 22% 21% Surface dose 49% 18% Peripheral dose 41% Li et al, ARRS 2006 Effect of CT Adaptations on Dose Steps for Lowering Dose 50% decrease in ma = 50% dose reduction kv = 40% dose reduction Increase in pitch = dose decrease Thicker slices = dose decrease DECREASE IN Tube current Tube potential Gantry rotation time * Scan length Overlap scanning Number of scan phases INCREASE IN Pitch (Table speed) * Beam collimation *Provided other scanning factors are kept constant Indication Appropriate Image Quality 151 lbs 162 lbs Radiation Dose from MDCT Exams A B C D CT dose 6.8 msv CT dose 2.2 msv 430 lbs 156 lbs CT dose 1.6mSv CT dose 18 msv 140 kvp NI-15 5 mm 0.8 sec 100 kvp NI mm 0.5 sec 120kVp NI-25 5 mm 0.5 sec 80kVp NI mm 0.5 sec CT dose 1.06 msv 14.3 msv 7.3 msv 5.5 msv 1.7 msv Obtained by EUR EN using an abdomen factor of 0.015*DLP and a pelvis factor of 0.019*DLP 4

dose Adjusts tube current Based on patient size From slice-to-slice (z modulation) Within each slice (xy angular modulation) Constant ma Reduced dose level based on scout Real time angular dose

AJR 2008, 1232 Mulkens Radiology 2005; 213 C AEC on Different Scanner Types SCANNER TYPE GE-64 Toshiba-64 ACE TRADE NAME Auto ma Smart ma Sure Exposure OPERATOR CHOSEN PARAMETER PATIENT SIZE ACE

5 Options for ma Reduction? Manual selection of a fixed ma Automated technology Automated Exposure Control (AEC) AEC changes ma to follow changing patient anatomy in order to maintain a constant image noise/quality & optimize dose Adjusts tube current Based on patient size From slice-to-slice (z modulation) Within each slice (xy angular modulation) Constant ma Reduced dose level based on scout Real time angular dose modulation A D B Graser AJR 2006; 659 Herzog et al. AJR 2008, 1232 Mulkens Radiology 2005; 213 C AEC on Different Scanner Types SCANNER TYPE GE-64 Toshiba-64 ACE TRADE NAME Auto ma Smart ma Sure Exposure OPERATOR CHOSEN PARAMETER PATIENT SIZE ACE Z-AXIS ACE ANGULA R ACE GOAL (Regardless of attenuation level) Noise Index Yes Yes Yes Constant image noise, within user prescribed minimum and maximum ma Standard Deviation Yes Yes Yes Noise Index and dose Noise index: to choose the desired image quality (image noise) NI is inversely related to radiation dose NI-15 Higher the NI, lower is the CT dose NI-35 Siemens-64 Philips-64 CARE Dose 4D Dose Right Reference Effective mas Reference Image Yes Yes Yes Constant image quality, with reference to a mas level for an average sized patient Yes Yes Yes Same image quality as reference image. 12 msv 4 msv Dose increases by 10% for a decrease in NI of 5% Dose decreases by 9% for a increase in NI of 5% Noise Index, Slice Thickness, and Relative Dose Reconstruction Slice Thickness (mm) Relative Dose NI NI NI NI NI Weight Based CT Protocol: Routine Abdomen Weight < 135 lbs lbs lbs Siemens (Care Dose 4D) kv Ref ma Pitch kv GE 16/64 (Auto ma 3D) Auto ma (minmax) Pitch Noise index Phillips 64 (Z-DOM) kv mas Pitch > 300 lbs Kanal K et al. AJR July 2007 vol. 189 no

When do want to use manually selected fixed ma?

low-kv selection Increased iodine contrast CTA studies 140 kv 100 kv Stiller et

2011 Utsunomiya et al, Eur Radiol. 2010 Marin et al, Radiology.

kv 2 Small and medium size patients NOISE Strategies for low kv (80-100)

350 ma Siegel MJ Radiology 2004; 233:515 Huda, et al.

AJR 2006 Abdominal width 34 Huda et al, Radiology 2000 Nakayama et al, AJR 2006

al, Radiology 2010 dose kvp 2 kvp Selection Based on Body Weight & Indication:

6 When do want to use manually selected fixed ma? Lung cancer screening chest CT CT colonography Ultra-low dose exams Benefits of low-kv selection Increased iodine contrast CTA studies 140 kv 100 kv Stiller et al, Eur J Radiol Perisinakis et al, Br J Radiol Utsunomiya et al, Eur Radiol Marin et al, Radiology Kim et al, AJR Hunsaker AR. AJR Godoy MC. Eur J Radiol Feuchtner GM. Eur J Radiol Benefits / Challenges of low-kv selection Reduction in radiation dose dose kv 2 Small and medium size patients NOISE Strategies for low kv (80-100) selection Body weight Body mass index (BMI) Workflow kv / 440 ma 120 kv / 350 ma Siegel MJ Radiology 2004; 233:515 Huda, et al., Med Phys 2004 Nakayama, et al. AJR 2006 Abdominal width 34 Huda et al, Radiology 2000 Nakayama et al, AJR 2006 Schindera et al, Radiology 2008 Szucs-Farkas et al, Invest Rad 2008 Guimarães et al, Radiology 2010 dose kvp 2 kvp Selection Based on Body Weight & Indication: CTA Tube potential lbs > lbs < 150 lbs kvp ma= THE OTHER OPTION Automated kv Selection Technology A tool which automatically adjusts kv for body size determined from topogram and the exam type Up to 60% dose reduction 120kvp 100kvp 80kvp > 300 lbs= 140 kvp 6

MDCT protocols into 3-4 groups MGH CT Dose Fact Sheet

Hi-Contrast CTA/CTU/CTC Arterial phase Screening

(fixed) Low kvp options ma optimized Low kvp Low ma

Renal stone Post catheter drainage Crohn s

8 87% 90% 85% msv Initial scan Standard dose CT 1.

Category Std dose CT ULD CT CTDI msv CTDI msv Over

7 MDCT protocols into 3-4 groups MGH CT Dose Fact Sheet Low-Contrast I+ phase CECT (portal/nephro) Hi-Contrast CTA/CTU/CTC Arterial phase Screening Stone/CTC Post Procedure Low ma options kvp+/- (fixed) Low kvp options ma optimized Low kvp Low ma Ultra-low dose approaches Radiation Dose-ULD Stone CT Renal stone Post catheter drainage Crohn s disease/pancreatitis % 90% 85% msv Initial scan Standard dose CT view KUB Follow up scan ultra-low dose CT Wt Category Std dose CT ULD CT CTDI msv CTDI msv Over all < 200 lbs > 200 lbs Weight & Indication Adapted Protocols Cancer Follow-up Weight Noise Index kvp ma Ref mas mas/ Pitch < 200 lbs > 200 lbs

Low Dose Imaging Dose -30% -50 % -70% Dose -90% CT Image Reconstruction Standard Filtered back

at low dose Artifacts in large patients and dense structures Reduced CNR Standard FBP Raw data

Statistical Iterative Reconstruction) MBIR (Model Based Iterative Reconstruction) Siemens: IRIS

(Fourth Generation) Toshiba: AIDR (Adaptive Iterative Dose Reduction) IRIS/ASIR/iDOSE/ADIR/SAFIRE

8mSv* Simple Comprehensive Advanced Blend FBP+IR Ideal System Few Iterations Advanced model Renal

Low noise Optimal IQ Low noise Better resolution FBP ASIR Veo/MBIR 120 kv, 10 ma, 0.5 rot 0.

8 Low Dose Imaging Dose -30% -50 % -70% Dose -90% CT Image Reconstruction Standard Filtered back projection (FBP) Makes several assumptions Time efficient NOT dose efficent Excessive image noise at low dose Artifacts in large patients and dense structures Reduced CNR Standard FBP Raw data recon Fast Image Data Space Slow Raw Data Space Iterative Reconstruction GE: ASiR (Adaptive Statistical Iterative Reconstruction) MBIR (Model Based Iterative Reconstruction) Siemens: IRIS (Iterative Reconstruction in Image Space) SAFIRE (Sinogram Affirmed IR) Philips: idose/idose4 (Fourth Generation) Toshiba: AIDR (Adaptive Iterative Dose Reduction) IRIS/ASIR/iDOSE/ADIR/SAFIRE (30-50%) MBIR/Veo (>50%) FBP VS. Partial IR VS. Full IR MBIR/VEO: ULD Abdomen Pelvis 0.8mSv* Simple Comprehensive Advanced Blend FBP+IR Ideal System Few Iterations Advanced model Renal tumor in a horse-sh shaped kidney Dose report CPU CPU CPU Simple Better IQ Fast Low dose High noise Low noise Optimal IQ Low noise Better resolution FBP ASIR Veo/MBIR 120 kv, 10 ma, 0.5 rot 0.625mm slice thickness Courtesy: De Ann Haas GE *Obtained by EUR EN, using an abdomen factor of 0.015*DLP and a pelvis factor of 0.019*DLP 8

* The information about this product is being provided for planning purposes.

In clinical practice the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size,

A consultation with a radiologist and a physicist schould be made to determine the appropriate dose to obtain

6 HU up to 55% less noise 30% less up noise to 70% less noise IRIS = 12.3 HU = 7.

(Take home points) Radiation does indeed have the potential to cause cancer at larger doses Cancer risk data at low

Barreto, Siemens Minimize CT (use MR or US) Patients < 30 yo Pregnant patients More efficient detectors $$ Technical

Protocol optimization: Tube current modulation Full iterative reconstruction $$$$$ $ Protocol optimization: Clinical

Overview Utilization One of the highest volume medical drugs used compared with any other pharmaceutical Over 80

9 * The information about this product is being provided for planning purposes. The product is pending 510(k) review, and is not yet commercially available in the U.S. In clinical practice the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist schould be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. SAFIRE FBP = 26.8 HU 35% less noise WFBP = 17.6 HU up to 55% less noise 30% less up noise to 70% less noise IRIS = 12.3 HU = 7.8 HU SAFIRE What should we tell patients? (Take home points) Radiation does indeed have the potential to cause cancer at larger doses Cancer risk data at low radiation doses is controversial In adults: Minimal to no increased cancer risk from a single CT exam Courtesy: Mitya Barreto, Siemens Minimize CT (use MR or US) Patients < 30 yo Pregnant patients More efficient detectors $$ Technical innovations Blended FBP and iterative reconstruction More efficient filters $ $$ Other design innovations $-$$$ Protocol optimization: Tube current modulation Full iterative reconstruction $$$$$ $ Protocol optimization: Clinical indication $ Protocol optimization: kvp $ Protocol optimization: Pitch $ End user Initiatives Contrast Media: An Overview Utilization One of the highest volume medical drugs used compared with any other pharmaceutical Over 80 million doses administered with iodinated intravascular contrast media in 2003 corresponding to approximately 8 million liters Persson, PB. Nephrol Dial Transplant CM Safety CT CM AE s at 6 Partners Hospital Safety profile of non-ionic CM is well established AE s %, majority minor Severe AE s uncommon but still encountered Severe CM extravasation uncommon influenced by the quality of IV access and injection rate 54 9

10 AE s with Iodinated CM: ACR Classification Systemic (0.2%) Local Mild Moderate Sever Delayed CM Extrav Rash Itchy Sneeze Vasovagal Tachycardia Reassure Vitals Benadryl Atropine Wheeze Hypotensive Pulm edema CHF Severe Tachy ACLS Fluids/Lasix Epinephrine Code Anaphylaxis Collapse Laryngeal angioedema Code ACLS Rash CIN Fragile veins Power inj Rapid bolus Flush Patch Warm/cold compress Contrast Media Induced Nephropathy (CIN) CIN can be defined as either of the following: Relative increase of serum creatinine (SCr) from baseline values from 25%- 50% OR Absolute increase of SCr from 0.5 to 1.0 mg/dl Risk Factors for CIN Risk Factors for CIN There is general consensus that renal insufficiency and diabetes are major risk factors for CIN, particularly when coexisting. Secondary Diabetes mellitus, alone Cardiovascular disease and diuretics Advanced age (>75 years) Multiple myeloma (in dehydrated patient) Hypertension Uricosuria The NEPHRIC Study, 2003: IOCM & LOCM Briguori et al., 2005: IOCM & LOCM 129 patients with renal impairment and diabetes mellitus undergoing cardiac or peripheral angiography Baseline SCr: > 1.5 mg/dl CIN endpoint: 0.5 mg/dl SCr from baseline Overall incidence of CIN: Visipaque-320: 2/64 (3.1%) Omnipaque-350: 17/65 (26.2%) Difference: p<0.002 IOCM Iodixanol (Visipaque-320, 300mOsm/kg) LOCM iobitridol (Xenetix -350, 915 mosm/kg) Renally-impaired (SCr > 1.5 mg/dl) undergoing cardiac catheterization All patients were well hydrated (standard protocol) and received NAC Overall incidence of CIN: Visipaque: 3/110 (2.7%) Xenetix: 4/115 (3.5%) NEJM. 2003; 348: Kidney Int. 2005; 68:

11 CIN and Intravenous Contrast Administration CIN with Head-to-Head Comparisons Risk Patients Receiving I.V. Contrast Material Study LOCM (monomers) Carraro et al (1998) 0/32 (iopromide) IOCM Criteria (Iodixanol) 1/32 50% SCr Kolehmainen et al (2003) IMPACT Barrett et al ACTIVE Catalano /25 (Xenetix) 0/77 (iopamidol) TOTAL 4/210 (3%) 0/76 5/72 4/25 44 m/l SCr 2/ mg/dl SCr 12/205 (6%) Prevention of CIN Identify at risk group Estimate egfr from S.Cr: Use MDRD or other equations (egfr> 60mL/min) Discontinue nephrotoxic drugs Prevention of CIN Keep the dose as low as possible-but still get a diagnostic study 70-80% of the calculated dose usually reasonable Space studies > 72 hours if possible With IV LOCM, risk of CIN is low For current CM (LOCM & IOCM), osmolality is not a significant factor for reducing the incidence of CIN Preventing Contrast Nephropathy: Screening and risk stratification Pharmacologic prophylaxis and CIN prevention Pharmacologic agent Study design Results Atrial natriuretic peptide Prospective, randomized No benefit Dopamine Prospective, randomized Worsened or no benefit Endothelin antagonist Prospective, randomized Worsened CIN Adenosine antagonist Prospective randomized No benefit Estimated GFR <30 ml/min/1.73 m2 Estimated GFR ml/min/1.73 m2 Estimated GFR >45 ml/min/1.73 m2 Ca channel blocker Prospective Not studied adequately Fenoldopam Mesylate Prospective, randomized No benefit NO CONTRAST* Prophylactic Measures + CONTRAST Prostaglandin E1 Prospective randomized Further studies required. N-acetyl Cysteine Prospective randomized Mixed benefit 11

12 Summary Incidence of CIN with CT in high risk group is 2-7% Majority are self limiting IV saline hydration or nephroprotective drug use is encouraged to reduce CIN but their benefits in CT are unclear Choice of non-ionic CM has no substantial benefit in reducing the CIN risk Summary CT dose is the biggest threat to radiology dept Critical to invest efforts in lowering CT dose and Education Optimize CT protocols based on body size, age and clinical indications Weight adapted ma and kvp reductions Limit scan acquisition phases and scan length Use thicker slices (5 mm) and include Multiplanar reconstructions Summary Low dose CT scans with IR technique allows substantial radiation dose reduction while providing diagnostic image More drastic dose reduction with low kvp easier to apply Large Body Habitus scans are of optimal quality with modest dose reduction Moving towards the goal of sub msv to minimize risk and improve CT utilization Thank you 12

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