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A view from the auditor Melbourne 5th October 2012

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1 A view from the auditor Melbourne 5th October 2012
Patient Safety in Radiation Oncology: Australian Edition A view from the auditor Melbourne 5th October 2012 Ivan Williams, Joerg Lehmann, John Kenny, Jessica Lye, Leon Dunn

2 Why use / trust an auditor ?
So why would you let a bunch of guys (yokels?) like this into your facility to measure your equipment, and even if you did, why would you trust them? You, who have spend many days and weeks measuring, checking your very expensive equipment, with decades of experience and practice in the disciplines of medical physics, radiotherapy and radiation oncology, who are critically aware and concerned for the patient, what does an auditor, particularly the ACDS, offer? I submit to you that the answer has two parts, the first is a negative, defensive position based on risk avoidance, and fairly generic. The second is a positive approach, which is based on the improvement of the patients’ condition, to which I will provide explicit examples.

3 Defensive (negative) rationale
1045 patients There are numerous examples of mis-treatments internationally. Many have been described in this workshop, and I won’t repeat the discussion. However, it is worth saying that the worst incidents are systemic, and have incorrect dosimetry as their root cause. Worst = longevity of mis-treatment and consequences of the error leading to 100’s of patients being mis-treated.

4 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 Know about Epinal, Staffordshire etc. Systemic Big errors usually due to basic dosimetry

5 Why audit “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 2010 Izewska J, et al., SSDL 58, June 2011 Ibbot, G.S., Followill, D.S., SSDL 58, June 2011. Know about Epinal, Staffordshire etc. Systemic Big errors usually due to basic dosimetry

6 Oversight panels with professional experts
Positive rationale A 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 Audit is what these people do. The ACDS has a staff of around 4 efts, all dedicated to audit related issues all the time. The ACDS program has expertise and abilities beyond the capacity of many radiotherapy facilities within its area of audit

7 Example I: Time

8 Example II: Technical expertise
Courtesy R.Ganesan, P Harty.

9 Example III: Equipment
ACDS recently purchased 7 new waterproof thimble chambers. ARPANSA calibrated them sequentially. All our audit kits have dedicated chambers, cables and electrometers. If we have a problem with one, it can be swapped out. Courtesy R.Ganesan, P Harty.

10 Positive rationale: Oversight
ACDS ARPANSA (CEO) Branch Head Medical Radiation Daily Administration Formal Responsibility Department of Health and Ageing MOU CAG Auditors Facilities & Professional Organisations Advise Approval of Documents CAG comprises of experts drawn from all three professions.

11 Technical Expertise: OSLD commissioning
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 So, what are nanoDots? nanoDots are passive solid state dosimeters containing an amount of Aluminium oxide doped with carbon. The size of the overall dosimeter is 1 x 1 x 0.2 cm and inside the casing is a retractable sensitive element 5mm in diameter and 0.2 mm thick containing a layer of Al203 crystal sandwiched between to polyester films. The sensitive element is light sensitive and is only brought out of the case during readout. The outer casing is bar-coded allowing for tracking of individual dose histories. 1.0 cm 1.0 cm

12 Commissioning - Overview
Reproducibility Signal depletion during readout Reader stability Fading Linearity Energy dependence So now to the methods, I will only touch on the methodology briefly in this section however we do have a paper coming out shortly which details in full all of the methodologies associated with commissioning. So I’ll briefly touch on methods to determine the reproducibility, signal depletion per read, the reader stability, fading, linearity and the energy dependence. Why? Accurate calculation of absorbed dose requires a correction for each of these. Kf, Kl, Ke, Kr

13 Signal depletion per read
These are the results for the signal depletion per readout. A single nanoDot was repeatedly readout 190 times and the depletion in signal recorded. A linear fit to the data indicates a decrease of about 0.028% per read, which is consistent with findings in the literature of 0.03 – 0.04%. The lower depletion value obtained in our work is most likely due to a newer generation reader. The consequence of this is that each dosimeter can be re-read a number of times and depletion can be accounted for. 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.

14 Linearity Decrease in sensitivity as the absorbed dose to the nanoDot OSLD increases. The sensitivity = cGy per unit signal. Shown here is the linearity exhibited by nanoDots. We see that nanoDots exhibit a linear response up to approximately 3 Gy followed by a supralinear response at doses above this. The graph of sensitivity versus absorbed dose, where sensitivity is defined as cGy/signal is used to determine the linearity factor which is applied to the audit readings. In audit scenarios the accumulated dose to nanoDots does not exceed 3 Gy. Supralinear response with the degree of supralinearity being dependant on the accumulated dose.

15 Energy Dependence 2.8 % w.r.t response at 6MV
Slight energy dependence for MV photons up to 1% relative to 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. Energy dependence is important in any dosimeter used for radiotherapy applications, we have determined the dependence for Co-60 6 , 10 and 18 MV photons, and a range of electron energies. There is a slight energy dependence for photon energies of about a percent with respect to the response at 6 MV. Low energy electron beams exhibit similar difference however a 2.8% discrepancy compared to 6MV was found for 20 MeV electrons. These results are consistent with reported findings and the manufacturers statement 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)

16 Daudit = [(Counts.kr –Counts(bg).kr(bg).kf(bg)) kf ] ECF.S.kE.kL
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. " So why are we determining all these factors, well aside from the obvious reason of characterising the dosimeter, in an audit analysis for Level I we take into account the element correction factor, the energy dependence, the linearity and fading as well as a reader correction for variation in the readers performance over time. Using this methodology, we have now initiated live photon beam audits of radiotherapy centres nationwide, with electrons on the way shortly, and if there is time ill briefly show you some preliminary data.

17 Block Factors The dose delivered to the block, Daudit, is then converted to the equivalent dose under the reference conditions of the facility, Dref. The block dose requires corrections for; the different distance and depth between audit and reference conditions, the reduced scatter in the small block compared to a full scatter water phantom; and the difference between the block material and water. The BF was modelled with BEAMnrc/DOSXYZnrc and compared to measured block factors for the ACDS linac. The modelling of the BF was then extended to a range of beam qualities for each nominal photon and electron energy to cover the existing range of beam qualities in Australia.

18 Fading corrected for readout

19 The ACDS: An auditing program
In 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 There was debate about the model to be trialled, that selected was to utilise the dosimetric expertise at ARPANSA, rather than a clinical or academic environment.

20 The service is free and voluntary
ACDS trial Fundamentally To increase the safety of radiotherapy within Australia via: Three level audit – Level I, II and III. National coverage Private and public clinics Interaction with professional colleges – Level Ib The service is free and voluntary Within MoU Extant to MoU

21 Australian Context: Risk contributors
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 So Australian radiotherapy, what’s going on?

22 ACDS Audit Levels Diagnostic Imaging Target Outlining Treatment
Planning Beam Calibration Patient Setup Treatment Delivery Record and Verify Level III Level I Level II Level I: Linac output under reference conditions Level II: Treatment planning and delivery Level III: End-to-End test Based on T.Kron et al., IJROBP 52(2), 566–579, 2002

23 Audit reporting 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%” 2 sigma = = 95.4 % 23

24 Methodology & Design Dose to Patient Dose Delivery / Dose Calculation
Level I Audit Level II Treatment Delivery Beam Modelling Level III Lung / Thorax 4D Planning / Intensity Modulated H&N Pelvis Breast Phantom geometry Calc Algorithm Simulation Targeting Inhomogeneity Dose to Patient Dose Delivery / Dose Calculation Level 2 includes multiple points of measurement in a beam enabling a Beam Quality parameter or in-beam match parameter to be determined. Dose to Water 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.

25 Methodology & Design Dose to Patient Dose Delivery / Dose Calculation
Lung / Thorax Dose to Patient H&N Pelvis Breast 4D Planning / Delivery Intensity Modulated Level III Audit Phantom geometry Calc Algorithm Simulation Targeting Inhomogeneity Dose Delivery / Dose Calculation Level II Audit Treatment Delivery Beam Modelling Level 2 includes multiple points of measurement in a beam enabling a Beam Quality parameter or in-beam match parameter to be determined. Level I Audit Dose to Water 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.

26 Methodology & Design Dose to Patient Dose Delivery / Dose Calculation
Lung / Thorax Dose to Patient H&N Pelvis Breast 4D Planning / Delivery Intensity Modulated Level III Audit Phantom geometry Calc Algorithm Simulation Targeting Inhomogeneity Dose Delivery / Dose Calculation Level II Audit Treatment Delivery Beam Modelling Level 2 includes multiple points of measurement in a beam enabling a Beam Quality parameter or in-beam match parameter to be determined. Level I Audit Dose to Water Similarly, issues arising with a Level II audit may be investigated and resolved with a Level I

27 Level I Passive 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%

28 Not shown: beam quality measurements, where we found action level
6 MV MV 18 MV

29

30 Level Ib – by consumer demand
On-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 ...

31

32 Original audits only, Not showing results of repeats, one repeat had OT now action level (electrons) and additional action level (photon) 6 MV ≥ 10 MV 6 MeV 8-9 MeV 12 MeV 15-16 MeV ≥ 18 MeV

33 Initial uncertainty did not include correlated uncertainty and used common factors for photon and electrons 6 MV ≥ 10 MV 6 MeV 8-9 MeV 12 MeV 15-16 MeV ≥ 18 MeV

34 Level II Diagnostic Imaging 3D Treatment Planning Patient Setup Treatment Delivery Record and Verify 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. The planning computer is given synthetic CT data which is used in the planning process. This ensures that issues arising from the CT process will not confound the outcome.

35 Level II – Basic Design Required: 40 % of all linacs in Australia.
Explain phantom, show lungs and point out measurement locations “This is what it looks like” Required: 40 % of all linacs in Australia. To-date: Testing and field trials Expected: ~40 %

36 Level III Entire 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 audited Expected: 20+ linacs The planning computer is given synthetic CT data which is used in the planning process. This ensures that issues arising from the CT process will not confound the outcome.

37 Level III Humanoid Phantom (Ann D Roger) goes through the complete chain of procedures a patient experiences in Radiation Therapy. Diagnostic Imaging 3D Treatment Planning Patient Setup Treatment Delivery Record and Verify 1 10 Explain phantom, show lungs and point out measurement locations “This is what it looks like” CIRS thorax phantom 37

38 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. We want the people who do this day by day, not physicist, not the charge RT

39 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 2 sigma = = 95.4 % 39

40 Level III – case 2  adjusted for points in low dose areas
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) 1 10 Field: 6x, 10 cm x 15 cm 45° wedge Prescription: 2 Gy to Point 1  adjusted for points in low dose areas Global reference is used instead of local

41 Level II - Field Description
Level II underpinning Level III Level II Field ID Level II - Field Description Level III reference Field 7 case 3 LAT open field, asymmetric Field 8 wedged field, Field 9 inhomogenity Field 10 wedged field Inhomogenity Example fields ACDS Reference Conditions. Measurement depth condition adjusted by adding or removing slabs of solid water from upper layer.

42 1 % error in pressure ~ 1 % error in dose
Recommendation I Review 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 1% pressure inaccuracy = 1 % dosimetric inaccuracy. Natjonal association of testing authorities.

43 Early lessons learned 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

44 ACDS Success Factors MoU defined audit targets – have been shown to be flexible Invitations to conferences, informal vocal support personally and at higher level Positive outcomes from review – recommendation to continue in existing or near existing format Start planning now – written document for reviews MoU defines these, having said that, interpretation of the MoU is allowable and on-going.

45 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 Level I overshoot (100*% v 60%) feeds into the long term plan, discussed within CAG, that the three audits will eventually be delivered over a three cycle, one per year. Ib has huge support from the professions, discussion in RORIC hinted that PPP sites would have an ACDS type Ib audit as a prequisite within the provider contract. Formalise annual ARPANSA meetings with AIR, RANZCR and ACPSEM – annual conference? 100 % = >95 %

46 Acknowledgements John Kenny Jörg Lehmann Leon Dunn Jessica Lye Tomas Kron Abel MacDonald Alison McWhirter Tracey Rumble Ramanathann Ganesan Peter Harty David Webb Duncan Butler Chris Oliver Peter Johnston There was debate about the model to be trialled, that selected was to utilise the dosimetric expertise at ARPANSA, rather than a clinical or academic environment. 'The Australian Clinical Dosimetry Service is a joint initiative between the Department of Health and Ageing and the Australian Radiation Protection and Nuclear Safety Agency' 46


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