Dosimetry Quality Assurance of Radiotherapy Facilities in the US

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Radiological Physics Center
David Followill, Ph.D.
and RPC Staff
Radiological Physics Center
• Formed in 1968 and located at
MD Anderson Cancer Center
(1 of 12 longest running grants).
• Our Mission is to assure NCI and cooperative groups
that institutions participating in clinical trials deliver
prescribed radiation doses that are comparable and
consistent, (minimize dose uncertainty), make
corrections and report findings to the community.
• Funded continuously for 44 years as cooperative
clinical trial groups have changed and expanded
internationally
• Use of remote and onsite dosimetry audits
RPC Scope of Monitoring
• Monitoring 1888 inst. participating in clinical trials
- includes 210 non-North American sites
41 countries (since 2006 45%)
- ~23,000 beams
- ~3500 machines
Components of RPC QA Program
1. Remote audits of machine output
1,888 institutions, ~14,000 beams measured with
TLD and OSLD in North America and
Internationally
2. Patient Treatment record reviews
474 charts reviewed for GOG, NSABP, NCCTG,
RTOG (brachytherapy)
3. On-site dosimetry reviews
41 institutions visited in 2011
(~150 accelerators/450 beams measured)
4. Credentialing - Phantoms
~500 irradiations in 2011
RPC Verification of Institutions’
Delivery of Tumor Dose
Reference calibration
(NIST traceable)
Correction Factors:
Field size & shape
Depth of target
Transmission factors
Treatment time
Tumor Dose
Evaluated by
RPC Dosimeters
Evaluated by
RPC visits and
chart review
Evaluated by
RPC phantoms
So, how are we doing?
OSLD/TLD Beam Output Checks
3-4% of the beams require a repeat
Comprehensive On-Site Audits
BEAM CALIBRATION
RPC Onsite Visits
Percent within 3% Criterion
100%
95%
90%
Photon
Reference Beam Calibration
Electron
85% of Inst. with ≥ 1 beam out of Criteria
Percent
TG-21
Implementation
80%
(since 2002)
TG-51
Implementation
Photons
75%
1975
OSLD/TLD (±5%)
7-11%
1980
1985
1990
Electrons
1995
6-12%
2000
2005
YEAR
Visits (±3%)
~13%
~15%
2010
On-Site Dosimetry Review Audit
Discrepancies Discovered (Jan. ’05 – Mar. ’11)
Number of Institutions
Discrepancies Regarding:
Receiving rec. (n = 156)
Review QA Program
115 (74%)
Photon Field Size Dependence (small FSD)
62 (40%)
Wedge Factor (WF)
50 (32%)
Off-axis Factors (OAF)/Beam symmetry
46 (29%)
Electron Calibration
27 (17%)
Photon Depth Dose
25 (16%)
Electron Depth Dose
18 (12%)
Photon Calibration
13 (8%)
Review Temp/Press Correction
11 (7%)
Change to TG-51
9 (6%)
Prescription Dose
Monitor UnitsElectron
= Cone Ratios
8 (5%)
(calibration)
dose) • (OAF)
Using Multiple
Sets of Data• (FSD) • (WF) • (depth
8 (5%)
Treatment record reviews
• RPC performs independent retrospective review and
recalculation of doses for RTOG, NCCTG and GOG brachy.
patients
• Errors in dose calculation and doses reported to study
groups are discovered and corrected
• The RPC review has resulted in changing the reported dose
on 546 (27%) of the1993 protocol patients reviewed since 2005.
- 13% are EBRT dose errors
- 87% are brachytherapy dose errors
We revise the dose data in 1 of every 3 charts
RPC Phantoms
Pelvis (10)
Thorax (10)
Spine (8)
H&N (30)
Liver (6)
SRS Head (10)
Benefits of RPC Phantoms
• Independent “end to end” audit
Phantom
Patient
• Imaging
• Planning/dose calculation
• Setup
• delivery
• Uniform phantoms and
dosimeters
• Standardized analysis
• Uniform pass/fail criteria
• Allows inst. to inst. comparison
• Established infrastructure
Patient
Phantom
Phantom Results
Phantoms Mailed
Comparison between institution’s plan and
500
delivered dose.
400
Phantom
H&N
Prostate Spine Lung
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
03
20
20
20
02
1139
313
120
686
162
22
Pass
200
(79%)
(82%) (63%)
928
265
78
Fail
187
35
13
Pass
100
(81%)
(85%) 5%/3m
(65%)
Criteria 7%/4mm 7%/4mm
m
Fail
211
48
42
0
RTOG Inst.
557
206
83
Acceptable (54%)
(20%)
(8%)
01
Irradiations
300
Year
Spine
SRS Head
Liver
Prostate
Lung
H&N
458
178
(75%)
361
59
(79%)
5%/5m
m
97
289
(28%)
Phantom Results
Comparison between institution’s plan and
delivered dose.
H&N
Prostate
Spine
Lung
Irradiations (all years)
1139
313
120
458
Pass (all years)
928 (81%)
265 (85%)
78 (65%)
361 (79%)
Fail (all years)
211
48
42
97
Irradiations (2011)
109
56
40
80
Pass (2011)
101 (93%)
45 (80%)
31 (78%)
68 (85%)
Fail (2011)
8
11
9
12
Criteria
7%/4mm
7%/4mm
5%/3mm
5%/5mm
Failure rate doubles going to ±5%/3mm criteria
Why do we continue to find errors?
1. Too busy
2. Advanced technology/ Don’t understand process
3. Communication/Fear of punishment
4. Training/Failure to ask for help
5. Can’t accept the fact that an error could be mad
Human Errors!
WHO report on “Radiotherapy Risk Profile” states
that 60% of all radiotherapy incidents are
attributable to human error.
Let’s get past
these hurdles!
Questions?
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