Transcript Radiation safety and CT dose

PARM AUTUMN SYMPOSIUM
October 6 & 7, 2011
RADIATION SAFETY AND CT DOSE
Margaret “Peggy” Blackwood, MS, DABR
System Director, Radiation Physics
Radiation Safety Officer
West Penn Allegheny Health System
RADIATION SAFETY…WE’VE COME A LONG WAY
CT…WE’VE COME A LONG WAY
CT GROWTH
80 M CT/yr*
1 in 5
7M ped CT/yr*
10% growth/yr
*one phase
Single largest source of radiation to US population
Brenner D, Hall E. N Engl J Med 2007;357:2277-2284
POPULATION DOSES
MEDICAL IMAGING ~ DOUBLED BACKGROUND
1980
2006
Radiology, V 253, #2, Nov 2009
BENEFITS…. AND RISKS

Stochastic
 Cell
mutation
 Cancer
 No threshold; uncertainties below 100 mGy (10 rads)
 Linear relationship of risk with dose

Deterministic
 Cell
death
 Skin effects and cataracts
 Threshold doses ~1-2 Gy (100-200 rads)
STOCHASTIC RISKS
Review Article
Computed Tomography — An Increasing
Source of Radiation Exposure
David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc.
N Engl J Med, Volume 357(22):2277-2284, Nov 29, 2007
CT organ doses in range for which there is
direct evidence of a statistically significant
increase in risk of cancer
DETERMINISTIC EFFECTS

Brain perfusion studies
 3-7Gy
(300-700 rads)
PEDIATRIC CT DOSES

2001-Society for Pediatric Radiology (SPR)


“ALARA Conference Proceedings. The ALARA
Concept in Pediatric CT-Intelligent Dose Reduction”
2002-National Council on Radiation Protection
and Measurements (NCRP) Conference on CT
Dose
CONCLUSIONS OF EARLY CT CONFERENCES

Excess cancer incidence in those exposed to
radiation doses comparable to CT dose levels
 Small
but statistically significant excess of cancer
mortality over an individual’s lifetime
 Children are more sensitive to radiation than
middle-aged adults by factor of 10; girls are more
sensitive than boys
 Small risk per CT multiplied by large number of CT
exams is public health issue, particularly in children
LIFETIME RISK OF CANCER
Graph shows lifetime attributable risk of radiation-induced cancer incidence, as a function of
age at exposure for males and females.
Hricak H et al. Radiology 2011;258:889-905
©2011 by Radiological Society of North America
CONCLUSIONS OF EARLY CT CONFERENCES

CT dose reduction important but must maintain
acceptable diagnostic image quality
 Appropriateness
of study
 Adjust CT doses to patient size (not fixed mA)
 Automatic dose reduction methods in CT scanners
 Standardize CT protocols; periodic review
 Dose reporting information CT exams
 Develop CT accreditation and QC programs
CT IMAGE QUALITY AND DOSE

Contrast-to-noise (CNR)
 Noisier
image as dose
reduced
 Loss of low contrast
detectability
CONCLUSIONS OF EARLY CT CONFERENCES

No consensus regarding single expression of
dose
 Effective
dose
 Organ dose
 CT dose index (CTDI)
 Dose length product

Dissemination of information and education
regarding risks and need for CT dose reduction
ALLIANCE FOR RADIATION SAFETY IN
PEDIATRIC IMAGING (“ALLIANCE”)

2008-Founded
 SPR,
AAPM, ACR, ASRT
 60+ organizations; 750,000 medical imaging
professionals

Promotes radiation protection for children
 Awareness
 Education
 Advocacy-based
Image Gently
social marketing campaign:
IMAGE GENTLY (pedrad.org/associations/5364/ig)

Tests/Procedures
 CT
 Fluoroscopy
 Interventional
Radiology
 Nuclear Medicine

What can I do?
 Parents
 Radiologist
 Pediatricians
 Radiologic
technologists
 Medical physicists
IMAGE GENTLY (pedrad.org/associations/5364/ig)

What can I do? – Radiologists
 Comprehensive
Background & Guidance Document
 Review
of pediatric CT dose and strategies to manage
radiation dose
 “Medical
Radiation in Children”-powerpoint
 Image-Gently Web-based Practice QI Program
 Articles and Resources

How to Develop CT Protocols for Children
ED VISITS WITH CT UNDER AGE 18
Graph illustrates number of ED visits with CT from 1995 to 2008 in patients younger than 18
years.
Larson D B et al. Radiology doi:10.1148/radiol.11101939
©2011 by Radiological Society of North America
IMAGE GENTLY (pedrad.org/associations/5364/ig)

What can I do? – Technologists
 On-line
educational modules
 CT Practice Standards
 The Increasing Use of CT and its Risks
 Patient Dose from CT - Literature Review*
 ASRT White Paper: Computed Tomography in the
21st Century: Changing Practice for Medical Imaging
and Radiation Therapy Professionals*
ASRT WHITE PAPER: CT IN THE 21ST CENTURY

2007-Consensus Conference
 Increasing
use of CT technology is changing
practice faster than educational institutions,
vendors, medical providers and regulators expected
 Medical
imaging professionals need more
education in CT technology, including operation,
application and dose optimization to ensure patient
safety
 Challenges:
insufficient educational programs, educated
RTs in CT, education and training of entry level and
experienced CT techs
IMAGE WISELY (IMAGEWISELY.ORG)
Radiation Safety in Adult
Medical Imaging
IMAGE WISELY (IMAGEWISELY.ORG)

Sections for imaging professionals: physicians,
RTs and medical physicists; referring
practitioners and patients
 Take
the “Image Wisely” pledge
 Educational sections
 ACR Appropriateness Criteria
 Download
 American
for mobile devices
Imaging Management Patient Safety: Ask
AIMEE (interactive patient exposure calculator)
IMAGE WISELY (IMAGEWISELY.ORG)

Patient Medical Imaging Record
IMAGE WISELY (IMAGEWISELY.ORG)

Education, resources and links to websites
 CT
Equipment: Operation, Performance
 CT Protocols
Design methodologies
Protocols from other sites
 ACR Appropriateness Criteria
 Online communities for CT tech questions and info
CT PROTOCOL DEVELOPMENT & QA

Establish set CT protocols for each indication by
scanner, to optimize image quality and dose
 Vendor
protocols are not optimized
 Begin with most frequently performed exams
 Include all aspects of exam, e.g. patient positioning,
nursing instructions, exam parameters,
reconstruction/reformatting instructions, CTDI and
DLP reported values
 Protocol team(s) should include radiologist(s), CT
technologist(s), physicist(s) and administrator(s)
CT PROTOCOL DEVELOPMENT & QA

Establish set CT protocols…
 Benchmark
with published protocols and doses
 Develop consensus among radiologists regarding
image quality requirements
 Establish ONE standard of care
 Fully understand and utilize automatic dose
reduction techniques on CT scanner:
Establish criteria for automatic dose reduction
parameters, e.g. reference mAs, noise index, etc.
CT PROTOCOL DEVELOPMENT & QA

Develop policy and procedure for use of
reviewed and approved CT protocols
 radiologists
should not request and technologists
should not manually modify approved CT protocols

Develop a process to regularly review CT
protocols
 to
ensure they have not been modified and cannot
be improved further
HOW TO DEVELOP CT PROTOCOLS FOR CHILDREN
Abd-baseline
kVp=120
mA=200
Time=0.5s
Abd Pitch=1
PA thickness
(cm)
Approximate
age
mAs RF
Est mAs
mAs RF
Est mAs
9
Newborn
0.43
43
0.42
42
12
1 yr
0.51
52
0.49
49
14
5 yr
0.59
59
0.57
57
16
10 yr
0.66
66
0.64
64
19
15 yr
0.76
76
0.73
73
22
Sm adult
0.90
90
0.82
82
25
Med adult
Baseline
100
0.91
91
31
Lg adult
1.27
127
1.16
116
Abdomen
Th Pitch=1
Thorax
RF=Reduction factor; Est mAs = Baseline *RF
CT DOSE METRICS
CT DOSE METRICS
CT DOSE METRICS
CT DOSE METRICS

CTDIv
 Accounts
for beam width, detector configuration
and pitch
ACR CTDIv Pass/Fail & Reference Doses
CT Exam
CTDIv (mGy)
Pass/Fail
CTDIv (mGy)
Reference Level
Adult Head
80
75
Adult Abdomen
30
25
Ped Head (1 y.o.)
To be determined
To be determined
Ped Abd
(5 y.o., 40-50#)
25
20
CT DOSE METRICS

CTDIvol is NOT Patient Dose
 Reference

standard for radiation output of CT
Limitations
 Multi-detector
(MDCT) wider beam
 Phantom shorter than patient torso
 Underestimation of scattered radiation
 as much as 40%
 Not valid when table does not move, e.g. brain
perfusion or wide cone-beam systems
CT DOSE METRICS

CTDIvol
 Displayed
 Allows
on scanner console PRIOR to scan
operator to confirm proper protocol in use
 Included
in DICOM “dose report” or “patient dose
report”; reinforcing incorrect belief that CTDI is a
measure of patient dose

Patient dose is directly dependent of size and
shape of the patient
CT DOSE METRICS

CTDIvol
 Displayed
 Allows
on scanner console PRIOR to scan
operator to confirm proper protocol in use
 Included
in DICOM “dose report” or “patient dose
report”; reinforcing incorrect belief that CTDI is a
measure of patient dose

Patient dose is directly dependent of size and
shape of the patient
CT DOSE METRICS

Size-specific dose estimate



Conversion factor based on
patient size to estimate
patient dose (mGy)
Organ dose estimation not
possible with this method
Effective dose (mSv) cannot
be estimated
CT DOSE METRICS

Effective diameter
 Calculated
 Lateral + AP
 Lateral or AP only
 Eff dia = (APxLAT)1/2

Look up tables by effective
diameter method and CTDI
phantom utilized
CT DOSE METRICS
32 cm PMMA phantom
ACR report 2004
CT DOSE METRICS

Effective dose (mSv)
 Absorbed
dose to each organ
 Tissue-weighting factor-accounts for radiosensitivity
of each tissue irradiated
 Whole body effective dose equivalent
Effective dose=S(wT*organ equivalent dose)
wT = tissue weighting factor
TISSUE WEIGHTING FACTORS
Tissue
ICRP 26 (1977)
ICRP 60 (1991)
ICRP 103 (2007)
Gonads
0.25
0.20
0.08
Red bone marrow
0.12
0.12
0.12
Lung
0.12
0.12
0.12
Colon
0.12
0.12
Stomach
0.12
0.12
0.05
0.12
Bladder
0.05
0.04
Liver
0.05
0.04
Esophagus
0.05
0.04
0.05
0.04
0.01
0.01
0.01
0.01
Breast
Thyroid
0.15
0.03
Skin
Bone surface
0.03
Brain
0.01
Salivary glands
0.01
Remainder
0.30
0.05
0.12
41
STOCHASTIC RISK ESTIMATES
Statistically significant increase in cancer at
doses > 10 mSv
 Radiation risk: 1/1000 per 10 mSv

 Averaged
across all ages and genders
Normal background risk of cancer:400/1000
 Total increased risk: 401/1000

NEJM, Aug 2009, Fazel et al
https://prc.highmark.com/rscprc/hbcbs/pub
Highmark Radiology Management Program
Radiation Safety Awareness Program


Highmark/NIA identify “at-risk” patients
Dose Limit Threshold, equal to or greater than 50
mSv, patient’s cumulative radiation exposure based
on Highmark claims data

“a level that has been identified as causing a statistically
(epidemiologically) significant increased risk of developing
radiation-associated cancers
RADIATION SAFETY AWARENESS PROGRAM

Goals
 Raise
awareness regarding radiation exposure
 Risk v benefit
 Alternative studies
 How results of study will impact on patient
management
 Identification of patient’s prior imaging studies
 Evaluate necessity of repeat studies
 Consider discussing information with patient
RADIATION SAFETY AWARENESS PROGRAM

Physicians notified when preauthorization requested
 Offered NIA peer discussion
 Dose Limit Threshold Notification sent with
authorization or adverse determination letter
 “Important Note: The patient’s level of radiation
exposure does not impact the preauthorization or
decision-making process for requested imaging
studies.”
 Does not apply to patients with cancer diagnosis
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)

Radiation Risks of Diagnostic Imaging
 Right
test
 Right dose
 Effective processes
 Safe technology
 Safety culture
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)




Alert focused on diagnostic imaging, NOT therapeutic
radiation or fluoroscopy (i.e. CT)
Addressing contributing factors to eliminate avoidable
radiation dosing
Activities that can help eliminate avoidable radiation
doses
11 recommendations with 21 specific actions
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)





Comprehensive patient safety program, including
education about dosing in imaging departments
Training on how to use complex new technology
Knowledge regarding typical doses
Clear protocols that identify the maximum dose for
each type of study
7 other recommendations…education,
communication, equipment checks,…
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)

Right test
 Use of alternative non-ionizing tests
 Create and implement processes that enable
radiologists to provide guidance to and dialogue
with referring physicians regarding the appropriate
use of diagnostic imaging using the ACR
Appropriateness Criteria
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)

Right dose
 Adhere to ALARA
 Adhere to Image Gently and Image Wisely guidelines
 Provide reference doses, with ranges, to MDs and
techs, based on anatomy, study purpose and pt size
 Radiologists should ensure that the proper dosing is
in place for the patient being treated
 Annual or bi-annual protocol review
 Track doses from repeat exams; address & resolve
 Record dose/exposure in summary report of findings
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)

Effective processes
 Policies and procedures delineating staff
responsible for approving changes to password
protected protocols; for monitoring new
developments; control of password by RS “group”
 P & P delineating physical RS measures; e.g. lead
 Expand RSO role to explicitly include patient safety
and involve RSO in Patient Safety Committee
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)

Safe technology
 Organization-wide audit survey of rad equip;
centralize quality and safety performance under
physicist, RSO, RS group
 Qualified medical physicist to test all diagnostic
equipment annually and review scanning protocols
and doses
 Ensure QC and PM testing done; delineate
responsibilities in writing
 Invest in technologies that optimize or reduce dose.
TJC SENTINEL EVENT ALERT, ISSUE 47 (8/23/11)


Safety culture
 Promote safety culture for safe use of diagnostic
radiation
Additional recommendations
 Endorse national radiation dose tracking registry
 Encourage manufacturers to incorporate dosage
safeguards into EMR and national dose registry
 Support stricter regulations to eliminate avoidable
imaging and monitor the appropriateness of selfreferred imaging studies
DOSE REDUCTION TECHNOLOGIES
Detector advancements
 Axial
Helical
 Multi-detector CT (MDCT)
 Automatic exposure control

 Z-axis
modulation
 Angular and Z-axis modulation
Dual source
 Iterative reconstruction methods (e.g. ASIR)

Graph shows typical scanner output level (expressed as volume CT dose index [CTDIvol]) for
a routine abdominal CT examination from the 1980s, when xenon detectors were used, to
2004, when 64–detector row CT systems were introduced.
Hricak H et al. Radiology 2011;258:889-905
©2011 by Radiological Society of North America
AUTOMATIC EXPOSURE CONTROL
DOSE REDUCTIONS IN CT ANGIOGRAPHY
Hricak H et al. Radiology 2011;258:889-905
©2011 by Radiological Society of North America
GOALS
Radiation Safety in Adult
Medically necessary
Medical Imaging
 Least invasive modality
 Discussion of options between radiologist and
referring MD
 Minimize study as appropriate
 “Right size” radiation dose
 Education for patients and medical personnel

SIGN THE IMAGE GENTLY AND IMAGE WISELY PLEDGES!
PROGESS…



CT doses 1/3 lower
than a decade ago
Expect 10-fold+ or
more reduction in
next few years
ACR National Dose
Registry-collect data
on all CT exams