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Transcript of A view from the auditor Melbourne 5 th October 2012 Ivan Williams, Joerg Lehmann, John Kenny,...
A view from the auditor
Melbourne 5th October 2012
Ivan Williams, Joerg Lehmann, John Kenny, Jessica Lye, Leon Dunn
Patient Safety in Radiation Oncology: Australian Edition
Why use / trust an auditor ?
2
1045 patients
Defensive (negative) rationale
International Context• Numerous international examples of radiation
oncology accidents• Analysis has shown that most systemic errors
could have been detected by independent external audit
• International audits have all found issues which needed to be resolved
4
Why audit
5
“Firstly and most directly, in every dosimetry audit programme, measured doses have been observed and reported which have been outside the required tolerances, in some cases significantly so.”
Thwaites DI, SSDL 58, June 2010Izewska J, et al., SSDL 58, June 2011Ibbot, G.S., Followill, D.S., SSDL 58, June 2011.
Positive rationaleA properly constructed auditing program has resources beyond
the capacity of any (many?) radiotherapy facilities.• Time
• Dedicated staff• Dedicated equipment • Technical expertise
• Oversight panels with professional experts
6
The ACDS program has expertise and abilities beyond the capacity of many radiotherapy facilities within its area of audit
Example I: Time
Example II: Technical expertise
Courtesy R.Ganesan, P Harty.
Example III: Equipment
Courtesy R.Ganesan, P Harty.
10
ACDS
ARPANSA (CEO)
Branch HeadMedical Radiation
Daily Administration
Formal Responsibility
Department of Health and Ageing
MOU
CAG
Auditors
Facilities & Professional
Organisations
AdviseApproval of Documents
Positive rationale: Oversight
• Al2O3:C (Sapphire) nanoDotTM OSLDs • Size: 1x1x0.2 cm3
• Retractable Active element: 5 mm diameter, 0.2 mm thick• Material: Aluminium Oxide doped with Carbon• Bar-coded for tracking
1.0 cm
1.0
cm
Technical Expertise: OSLD commissioning
Commissioning - Overview• Reproducibility• Signal depletion during readout • Reader stability• Fading• Linearity• Energy dependence
Why? Accurate calculation of absorbed dose requires a correction for each of these. Kf, Kl, Ke, Kr
y = -0.02840x + 100.03959R² = 0.98430
93
94
95
96
97
98
99
100
101
0 50 100 150 200
Nor
mal
ised
Sig
nal
(%)
Read #
Linear (Reader 1 - Sn: 11340531)
Each readout of the dosimeter depletes the signal by 0.028%.
• Consequence: Each dosimeter can be re-read a number of times and corrected to reduce readout uncertainty.
Signal depletion per read
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0 200 400 600 800 1000 1200 1400
Sig
nal
x 10
0000
Dose (cGy)
y = -0.058ln(x) + 1.2816R² = 0.9834
0.80
0.85
0.90
0.95
1.00
1.05
1.10
0 200 400 600 800 1000
[cG
y/si
gnal
] / [c
Gy/
sign
al(1
00cG
y)]
Dose (cGy)
(a)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0 200 400 600 800 1000 1200 1400
Sig
nal
x 10
0000
Dose (cGy)
y = -0.058ln(x) + 1.2816R² = 0.9834
0.80
0.85
0.90
0.95
1.00
1.05
1.10
0 200 400 600 800 1000
[cG
y/si
gnal
] / [c
Gy/
sign
al(1
00cG
y)]
Dose (cGy)
(b)
• Supralinear response with the degree of supralinearity being dependant on the accumulated dose.
• Decrease in sensitivity as the absorbed dose to the nanoDot OSLD increases.
• The sensitivity = cGy per unit signal.
Linearity
Slight energy dependence for MV photons up to 1% relative to response at 6MV
2.8 % w.r.t response at 6MV
Consistent with (Aznar et al., 2004; Jursinic, 2007; Viamonte et al., 2008), along with the manufacturers stating that there is little to no energy dependence.
Electron beams show similar dependence (1 – 2%) with a larger measurement error associated with higher energies (18 – 20 MeV)
Energy Dependence
• The absorbed dose can be directly calculated using the following equation:
Daudit = [(Counts.kr –Counts(bg).kr(bg).kf(bg)) kf ] ECF.S.kE.kL
– ECF is the individual element correction factor defined as the ratio of the mean batch counts, after 100 cGy irradiation, to the individual OSL counts, after 100 cGy irradiation.
– S is the batch sensitivity, in cGy/counts, to 100 cGy of 6 MV photons.– kE is the energy correction to account for the slight energy dependence in
OSLD response relative to 6 MV photons.– kL is the non-linearity correction to account for the non-linear sensitivity of
the OSLD, normalized to the sensitivity at 100 cGy.– kr is the reader correction to account for the daily variation in the OSLD
reader.– A reader correction, kr(bg), is also applied to the background signal.– kf is the fading correction to account for the reduced signal that occurs
between irradiation and readout date.– A fading correction, kf(bg), is also applied to the background signal from the
initial ECF measurement. "
Block Factors
The ACDS: An auditing programIn July 2010, the Australian Government funded a trial initiative to provide external, independent dosimetric verification for Australian radiotherapy centres: The Australian Clinical Dosimetry Service, ACDS.
Housed within Australian Radiation Protection and Nuclear Safety Agency, ARPANSA, under a Memorandum of Understanding, MoU.
Analysis of the service will be conducted in the third year to determine the outcomes of the ACDS
A decision will be made whether to continue, modify or terminate the program based on the outcomes
ACDS trialFundamentally
To increase the safety of radiotherapy within Australiavia:
1. Three level audit – Level I, II and III.2. National coverage3. Private and public clinics4. Interaction with professional colleges – Level Ib
The service is free and voluntary
20
Within MoU
Extant to MoU
Australian Context: Risk contributors• 50000+ Australians treated per year• On-going roll-out of new radiotherapy clinics and updating of
older machines – technology • Detection of errors within modern machines can be more
difficult in modern cancer therapies• Australian is BIG - logistics• Sparse population and large cities – regional centres, country
centres and some metropolitan centres do not have local support
• Staff shortages
21
ACDS Audit Levels
Level I: Linac output under reference conditionsLevel II: Treatment planning and delivery Level III: End-to-End test
Based on T.Kron et al., IJROBP 52(2), 566–579, 2002
DiagnosticImaging
TargetOutlining
TreatmentPlanning
Beam Calibration
Patient Setup
TreatmentDelivery
Recordand Verify
Level I
Level II
Level III
- based on auditors absolute measurement uncertainty ()- action level: 2, failed audit > 3- reporting to center: “Dose is 0.7 % high with a 2 of 4.2%”
Audit reporting
All audit rest on the fundamental dosimetry, however, as the investigation approaches the dose to patient, the multiple factors affecting the dose to the patient must be considered.
Level I Audit
Level II Audit
Treatment Delivery
Beam Modelling
Level III Audit
Lung / Thorax 4D
Planning /Delivery
IntensityModulated
H&N Pelvis Breast
Phantom geometry
Calc Algorithm
Simulation
TargetingInhomogeneity
Dose to Patient
Dose Delivery / Dose Calculation
Dose to Water
Methodology & Design
With an on-going audit program, such as the ACDS, a variety of Level II audit test capabilities provides a strong foundation for Level III audits and a fall-back approach when questionable Level III outcomes arise and must be investigated.
Methodology & Design
Level I Audit
Level II Audit
Treatment Delivery
Beam Modelling
Level III Audit
Lung / Thorax 4D
Planning /Delivery
IntensityModulated
H&N Pelvis Breast
Phantom geometry
Calc Algorithm
Simulation
TargetingInhomogeneity
Dose to Patient
Dose Delivery / Dose Calculation
Dose to Water
Similarly, issues arising with a Level II audit may be investigated and resolved with a Level I
Methodology & Design
Level I Audit
Level II Audit
Treatment Delivery
Beam Modelling
Level III Audit
Lung / Thorax 4D
Planning /Delivery
IntensityModulated
H&N Pelvis Breast
Phantom geometry
Calc Algorithm
Simulation
TargetingInhomogeneity
Dose to Patient
Dose Delivery / Dose Calculation
Dose to Water
Level IPassive dosimeter, TLD/OSLD, placed in the clinical beam in a regular, reproducible environment with well understood conditions. External audit.
Was TLD (IAEA approach), changing to OSLD for logistical and operational reasons in July 2012
Required: 60% of all linacs in Australia.To-date: ~50%Expected: ~100%
27
-8
-6
-4
-2
0
2
4
6
8
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
Vari
ation
from
ACD
S (%
)
Beam ID
Output for All Photon Energies: 1st January 2011 to 18 September 2012Level I Audit (off-site, TLD, photon only)
ACDS Action Level (+/- 4.2%) ACDS Tolerance Level (+/- 6.3 %) Individual Photon Beam Measurement Mean
6 MV 10 - 15 MV 18 MV
-8
-6
-4
-2
0
2
4
6
8
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Vari
ation
from
ACD
S (%
)
Beam ID
Output for All Photon Energies: 1st Jan 2011 to 18 September 2012Level I Audit (off-site, OSLD and TLD photon only)
ACDS Action Level ACDS Tolerance Level TLD OSLD
Level Ib – by consumer demandOn-site measurement with chamber for photons and electrons
Required in many European Nations,
Required by Australian Radiation Oncology Practice Standards, criterion 15.1.
Recombination, polarity and output
Organisation supplies water tank, beam data
ACDS supplies chambers, electrometer, meters, cables ...
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115
Vari
ation
from
ACD
S (%
)
Beam Number
Level 1b Audit (On-site, Ionisation Chamber) as at 18 September 2012Outputs for All Photon & Electron Energies
Individual Beam Measurement ACDS Action Level 1.5% ACDS Tolerance Level 3.0%
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115
Vari
ation
from
ACD
S (%
)
Beam Number
Level 1b Audit (On-site, Ionisation Chamber) as at 18 September 2012Outputs for All Photon & Electron Energies
Individual Beam Measurement ACDS Action Level 1.5% ACDS Tolerance Level 3.0%
≥ 10 MV6 MV 6 MeV 8-9 MeV 12 MeV 15-16 MeV ≥ 18 MeV
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115
Var
iati
on fr
om A
CDS
(%)
Beam Number
Level 1B Audit (On-site, Ionisation Chamber) as at 18 September 2012Outputs for All Photon & Electron Energies
Individual Beam Measurement ACDS Action Level 1.5% ACDS Tolerance Level 3.0% Proposed New Action Level Proposed New Tolerance Level
≥ 10 MV6 MV 6 MeV 8-9 MeV 12 MeV 15-16 MeV ≥ 18 MeV
Level II
2D array of detectors placed in the clinical beam in a phantom of solid water. Lung slabs are added and measurement is compared with predictions from the computer planning system. Outcomes are derived from the spatial and dosimetric difference between the predicted and measured doses.
34
DiagnosticImaging
3D TreatmentPlanning
Patient Setup
TreatmentDelivery
Recordand Verify
Level II – Basic Design
Required: 40 % of all linacs in Australia.To-date: Testing and field trialsExpected: ~40 %
Level IIIEntire process check from CT to treatment with a human-like plastic phantom. Outcome is obtained from the spatial and dosimetric difference between measurement and prediction.
Required: 15 linacs within Australia.To-date: 9 linacs auditedExpected: 20+ linacs
36
Humanoid Phantom (Ann D Roger) goes through the complete chain of procedures a patient experiences in Radiation Therapy.
DiagnosticImaging
3D TreatmentPlanning
Patient Setup
TreatmentDelivery
Recordand Verify
CIRS thorax phantom
1
2 3 4 6 5 8
7 9 10
Level III
Radiation Therapists should conduct each of the steps in keeping with routine clinical practice so that the audit assesses the actual patient process.
Level III
Level III Dose Tolerances• measurement uncertainty () cannot be determined with
sufficient accuracy in the given complex geometry• clinical acceptability (5%) is used as a starting point for 3• points in low dose areas / clinically insignificant areas / not well
defined areas are reported but not scored (RNS)• and reporting will be re-evaluated over time as data comes in
with the goal of catching outlying results
Level III – case 2
Field: 6x, 10 cm x 15 cm 45° wedgePrescription: 2 Gy to Point 1
Location Expected dose Plan vs MX (local ref) Plan vs MX (global ref)
Point 1 – WDT ~200 cGy -0.63% (-2.51%, +1.22%)
Point 4 – WDT > 300 cGy 0.06% (-2.62%, +1.65%) 0.11% (-4.02%, +2.56%)
Point 7 – LAA ~4 cGy -17.1% (-42.9%, +18.3%) -0.37% (-1.02%, +0.34%)
average (min, max)
• adjusted for points in low dose areas• Global reference is used instead of local
1 2 3 4 6 5 8 7 9
10
Level IIField ID Level II - Field Description Level III
reference
Field 7case 3 LATopen field, asymmetric
Field 8case 3 LAT
wedged field, asymmetric
Field 9
case 3 LATopen field, asymmetric
inhomogenity
Field 10
case 3 LATwedged fieldasymmetric
Inhomogenity
Level II underpinning Level IIIExample fields
Recommendation IReview the accuracy of all barometers used for clinical dosimetry: Ensure that they are calibrated by a NATA accredited service, which is accredited for barometers.Ensure that the barometer(s?) is re-calibrated according to instructions.
1 % error in pressure ~ 1 % error in dose
42
Early lessons learned
43
• Air pressure issues– Barometer not calibrated (properly) or faulty– Airport pressure
• Equipment (ionization chambers) problems– Outdated styles– Slightly damaged Solvable administrative problems
• Understanding of calibration / QA process– Staff changes– Long living spread sheets – routine QA– Wrong calibration factor used
Successes & Challenges• Level I – ACDS will overshoot 100*% v 60% (accepted
by DoHA)• Level Ib – Outside MoU (accepted (commended?) by
DoHA)• Level II – ensure the ACDS hits target of 40 %• IMRT – Require plan for future• Prepare for review = prepare for post 2014• External Professional Expectations/Desires
45100 % = >95 %
AcknowledgementsJohn KennyJörg LehmannLeon DunnJessica LyeTomas KronAbel MacDonaldAlison McWhirterTracey Rumble
Ramanathann Ganesan Peter HartyDavid WebbDuncan ButlerChris OliverPeter Johnston
'The Australian Clinical Dosimetry Service is a joint initiative between the Department of Health and Ageing and the Australian Radiation Protection andNuclear Safety Agency'