MQSA Survey Considerations
Gary T. Barnes
Department of Radiology
UAB Medical Center
University of Alabama at Birmingham
X-Ray Imaging Innovations
Birmingham, Alabama
OUTLINE
• MQSA Regs — Pluses & Minuses
• Workflow Considerations
• Auditing Processor Performance
• Dose Creep
• Random Site Survey Observations
MQSA Regulations — Strengths
• Mandates Routine Quality Control
• Assesses Clinical Image Quality
• Mandates Physics Audits
• Mandates Phantom Image Quality
• Limits Breast Dose
• Mandates Random Audits
MQSA Regs — Weaknesses
• Processor Performance Not Addressed
• Inadequate AEC Perform Requirements
• Inadequate Cassette Exp Uniformity
Performance Requirements
• Digital QC and Phys Performance
Evaluations Left to the Manufacturer
• Mandates Annual FDA Audits
Inadequate AEC Perform Requirements:
• AEC Exp Reproducibility can be ± 5%
(should be < 2%)
• AEC Tracking is Required for 2 to 6 cm
Phantom Thicknesses
(should be 2 to 8 cm)
Inadequate Cassette Exposure Uniformity
Performance Requirements:
• Cass Exposure Uniformity is ± 0.30 OD
(should be ± 0.15 OD)
OUTLINE
• MQSA Regs — Pluses & Minuses
• Workflow Considerations
• Auditing Processor Performance
• Dose Creep
• Random Site Survey Observations
Audit Workflow Considerations
• AEC Exposure Reproducibility
• Cassette Exposure Uniformity
• AEC Tracking vs Phantom Thickness
and kVp
OUTLINE
• MQSA Regs — Pluses & Minuses
• Workflow Considerations
• Auditing Processor Performance
• Dose Creep
• Random Site Survey Observations
Rationale
Subpar processing can result in:
• Reduced film and image contrast
• Reduced film speed & increased dose
• Artifacts and increased image noise
Rationale (cont.)
• Processing and Processors are a major
problem area in mammography
• Processing artifacts are addressed in the
ACR Mammography QC Manual
• Processor performance — film speed and
contrast is not addressed by MQSA or ACR
Measuring film speed and film contrast
(ave gradient) and comparing these
values to ref values for the same type
of film is the key consideration
This can best be done by using a
calibrated box of film
The ref values can be the averages of
the sites audited
If one has sites using different types of
film, a box is needed for each type
Film speed is conventionally defined at
net density of 1.00
• This corresponds to gross density of 1.20
• In mammography the important background
density range is from to 1.50 to 2.00
• Film speed should be defined at a net density
of 1.25 or 1.50
Film ave gradient is conventionally defined
between net densities of 0.25 and 2.00
• This corresponds to gross densities of 0.45
and 2.20
• In mammography the important density range
is from to 1.00 to 2.50
• Film ave gradient should be defined between
net densities of 0.75 and 2.25
Additional information and insight
can be obtained by measuring:
• Developer & fixer specific gravity
(both processor & replen tanks)
• Developer & fixer pH
• Hypo retention and dark room fog
Processor Audit Form
Screen-Film System:
Processor Mfr
.
Model
.
Chemistry Mfr
Processing Time
.
Audit Film
.
Ref Film Speed
.
Ref Film Ave Grad
.Process Dev Sp Grav
Replen Dev Sp Grav
.
Emulsion No.
Site Film Speed
Site Film Ave Grad
Processor Audit Form (cont.)
Hypo Retention
Dark Rm Fog
.
Comments:
.
.
.
.
.
.
Auditing Processor Performance:
• Allows one to make specific
recommendations rather than
vague observations
OUTLINE
• MQSA Regs — Pluses & Minuses
• Workflow Considerations
• Auditing Processor Performance
• Dose Creep
• Random Site Survey Observations
• Ten years ago ACR phantom doses were
typically in the 125 to 175 mrad range
• Currently phantom doses are typically in the
175 to 225 mrad range
Two principle reasons for this dose creep are:
1. ACR Phantom and clinical film densities are
higher today than ten years ago
2. Ten years ago deep tank processors were
commonly used for mammography. Today
shallow tanks processors are more common
ACR Phantom Dose vs Film Density
350
Increasing ACR
Phantom Film Density
from 1.60 to 2.00
Increases Phantom
Dose by > 20%
250
150
50
1.0
1.5
2.0
Film Optical Density
2.5
3.0
Deep vs Shallow Tank Processor Speed
105
100
Deep Tank Processors
are 10% faster than
Shallow Tank Processors
Deep Tank
Shallow Tank
95
90
85
0
1
2
3
Sites
4
5
6
Additional Factors that have been found to
contribute to Dose Creep at individual sites
•
•
•
•
•
Subpar chemistry performance
Higher than acceptable grid Bucky factors
Slower than typical emulsion speed
kVp may be low and result in increased mAs
Low rad output and loss of film speed due to
reciprocity law failure at long exposure times
Kodak RP vs Brand X Chemistry
(Kodak Shallow Tank Processors)
100
Kodak RP Developer
Soln is 18% faster than
Brand X
90
Kodak RP Dev
Brand X Dev
80
70
0
1
2
3
Sites
4
5
Bucky Factors of 15 Grids
3
Range 2.24 — 2.83
Average
2.62
Std Dev
0.15
2.5
2
18 x 24 grids
24 x 30 grids
Emulsion Speed Variations
•
Emulsion speed variation of ± 5 % are typical
• Greater speed variations can occur
Effect of kVp on Dose
•
Decreasing the kVp by 1 kV increases
ACR Phantom Dose by 6.5%
•
If the measured kVp is 1 kV less than the
nominal 25 kVp, ACR Phantom Dose is 7%
greater than it would be if there was no
error in the measured kVp
Effect of Radiation Output on Dose
•
Depending on the mammo unit, radiation
output varies from 1000 to 2000 mR/sec,
i.e., a factor of 2.0x in exposure time
•
A factor of 2.0x longer exposure time will
increase ACR Phantom Dose by 4% due
to film reciprocity failure with Min-R 2000
Dose Creep
•
•
Dose creep occurs in mammography
•
ACR Phantom doses 250 mrad need to
be investigated by the medical physicist
to determine the cause or causes
One or more factors can result in
undesirably high ACR Phantom Doses
OUTLINE
• MQSA Regs — Pluses & Minuses
• Workflow Considerations
• Auditing Processor Performance
• Dose Creep
• Random Site Survey Observations
ACR Random Site Audits:
• ACR mandated to perform a limited number
of surveys each year
• All states visited in a cycle
• Audit team consists of a radiologist, medical
physicist and ACR staff mammo technologist
• Purpose is primarily educational and the goal
is to be of assistance to the sites
Physicist Role in Random Site Audits:
• Review physicist’s reports
• Review technologist’s QC records
• Acquire phantom image with TLD
• Evaluate phantom image quality
• Review technologist’s phantom scoring
• Review results with site
General Classification of Problems:
• Evaluation of unit
• Discrepancies in report
• Artifacts
• Image quality
• Technologist related
Unit Evaluation:
• Unit assembly evaluation
- Compression paddle loose at site visit,
no comment in report
- Grid assembly loose at site visit,
no comment in report
- Breast thickness off by > 0.5 cm in report,
not reflected in summary
- Power off not tested
- Auto compression release not tested
Unit Evaluation (cont.):
• Collimation Assessment
- Not in report
- Values in report not in regulatory compliance,
not reflected in summary
• Half Value Layer (HVL)
- HVL not checked for all targets
- HVL not checked over range of use
Unit Evaluation (cont.):
• Automatic Exposure Control (AEC)
- Insufficient check of AEC modes
- 8 cm not checked
- Significant density difference observed
between 18 x 24 and 24 x 30, no comment
- Modes used for physics evaluation are
different than used in clinical practice
Artifacts:
• Grid artifacts noticeable on phantom image
obtained during site visit, no comment
• Artifacts present on phantom QC images,
no comment
• Rh target artifact noted in data sheets,
no comment in summary
Image Quality:
• Technique of 28 kVp for 2 cm breast
• Magnification technique, long exposure time
• Physics phantom technique different than
used at site
• Phantom images noisy
• Marginal phantom image quality
• Bad phantom
Physics Report:
• Unit identification not noted
• Viewbox luminance not noted
• Summary of recommendations not given
• Problems indentified in data sheets are not
reflected in summary
• Discrepancies present between data sheets
and summary observations/recommendations
Technologist QC Program - Phantom:
• Improper scoring of phantom
• Phantom artifacts present - no follow up
• Disk density difference outside of ± 0.05
• Difference in phantom and clinical technique
• Marginal phantom images
• Phantom OD too low or too high
Technologist QC Program - Processor:
• Crossover not in records
• Error in performing crossover
• QC ref values not reset when necessary
• QC program spotty
• Dark room fog excessive
• Relative processor speed significantly low
Technologist Related:
• Noticeable dust present
• Cassette ID not clear
• Cassette storage
• Densitometer not functioning correctly
• OD of dense glandular areas < 1.0 OD
OUTLINE
• MQSA Regs — Pluses & Minuses
• Workflow Considerations
• Auditing Processor Performance
• Dose Creep
• Random Site Survey Observations
Conclusions
• Physicist have made and continue to make
important contributions
• Processor performance should be audited
• More care should be taken in conducting
audits and preparing reports
• Problems found should be communicated
• Greater care should be taken in reviewing
the technologist’s QC program