radiological physics center david followill, ph.d. and rpc staff
TRANSCRIPT
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
Reference calibration(NIST traceable)
Correction Factors:Field size & shape
Depth of targetTransmission factors
Treatment time
Evaluated byRPC Dosimeters
Evaluated byRPC visits and chart review
RPC Verification of Institutions’ Delivery of Tumor Dose
Tumor DoseEvaluated by
RPC phantoms
So, how are we doing?
OSLD/TLD Beam Output Checks
3-4% of the beams require a repeat
BEAM CALIBRATIONRPC Onsite Visits
75%
80%
85%
90%
95%
100%
1975 1980 1985 1990 1995 2000 2005 2010
YEAR
Per
cen
t w
ith
in 3
% C
rite
rio
n
Photon
Electron
TG-21 Implementation
TG-51Implementation
Comprehensive On-Site Audits
Reference Beam Calibration
Percent of Inst. with ≥ 1 beam out of Criteria
(since 2002)
Photons Electrons
OSLD/TLD (±5%) 7-11% 6-12%
Visits (±3%) ~13% ~15%
Discrepancies Regarding:Number of InstitutionsReceiving 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%)
Electron Cone Ratios 8 (5%)
Using Multiple Sets of Data 8 (5%)
Discrepancies Discovered (Jan. ’05 – Mar. ’11)
On-Site Dosimetry Review Audit
Monitor Units =Prescription Dose
(calibration) • (FSD) • (WF) • (depth dose) • (OAF)Monitor Units =
Prescription Dose
(calibration) • (FSD) • (WF) • (depth dose) • (OAF)
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)
Liver (6)H&N (30)
SRS Head (10)
Spine (8)
• Independent “end to end” audit
• Imaging
• Planning/dose calculation
• Setup
• delivery
• Uniform phantoms and dosimeters
• Standardized analysis
• Uniform pass/fail criteria
• Allows inst. to inst. comparison
• Established infrastructure
Phantom Patient
Benefits of RPC Phantoms
PhantomPatient
Phantom Results
Phantom H&N Prostate Spine Lung
Irradiations 1139 313 120 458
Pass686
(79%)162
(82%)22
(63%)178
(75%)Fail 187 35 13 59
Criteria 7%/4mm 7%/4mm5%/
3mm5%/
5mmRTOG Inst. Acceptable
557 (54%)
206 (20%)
83 (8%)
289 (28%)
Pass928
(81%)265
(85%)78
(65%)361
(79%)
Fail 211 48 42 97
Comparison between institution’s plan and delivered dose.
0
100
200
300
400
500
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
Year
Ph
an
tom
s M
ailed
Spine
SRS Head
Liver
Prostate
Lung
H&N
Phantom ResultsComparison 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
WHO report on “Radiotherapy Risk Profile” states that 60% of all radiotherapy incidents are
attributable to human error.
Human Errors!
Let’s get past these
hurdles!
Questions?