Presentation on theme: "A view from the auditor Melbourne 5 th October 2012 Ivan Williams, Joerg Lehmann, John Kenny, Jessica Lye, Leon Dunn Patient Safety in Radiation Oncology:"— Presentation transcript:
A view from the auditor Melbourne 5 th October 2012 Ivan Williams, Joerg Lehmann, John Kenny, Jessica Lye, Leon Dunn Patient Safety in Radiation Oncology: Australian Edition
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 2010 Izewska J, et al., SSDL 58, June 2011 Ibbot, G.S., Followill, D.S., SSDL 58, June 2011.
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 6 The ACDS program has expertise and abilities beyond the capacity of many radiotherapy facilities within its area of audit
Example II: Technical expertise Courtesy R.Ganesan, P Harty.
Example III: Equipment Courtesy R.Ganesan, P Harty.
10 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 Positive rationale: Oversight
Al 2 O 3 :C (Sapphire) nanoDot TM OSLDs Size: 1x1x0.2 cm 3 Retractable Active element: 5 mm diameter, 0.2 mm thick Material: Aluminium Oxide doped with Carbon Bar-coded for tracking 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
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
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. "
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
ACDS trial Fundamentally To increase the safety of radiotherapy within Australia via: 1.Three level audit – Level I, II and III. 2.National coverage 3.Private and public clinics 4.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 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 Diagnostic Imaging Target Outlining Treatment Planning Beam Calibration Patient Setup Treatment Delivery Record and 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 Intensity Modulated H&N PelvisBreast Phantom geometry Calc Algorithm Simulation Targeting Inhomogeneity 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 Intensity Modulated H&N PelvisBreast Phantom geometry Calc Algorithm Simulation Targeting Inhomogeneity 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 Intensity Modulated H&N PelvisBreast Phantom geometry Calc Algorithm Simulation Targeting Inhomogeneity Dose to Patient Dose Delivery / Dose Calculation Dose to Water
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% 27
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...
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 Diagnostic Imaging 3D Treatment Planning Patient Setup Treatment Delivery Record and Verify
Level II – Basic Design Required: 40 % of all linacs in Australia. To-date: Testing and field trials Expected: ~40 %
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 36
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 CIRS thorax phantom 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° wedge Prescription: 2 Gy to Point 1 LocationExpected dosePlan vs MX (local ref)Plan vs MX (global ref) Point 1 – WDT~200 cGy-0.63% (-2.51%, +1.22%) Point 4 – WDT> 300 cGy0.06% (-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
Level II Field ID Level II - Field Description Level III reference Field 7 case 3 LAT open field, asymmetric Field 8 case 3 LAT wedged field, asymmetric Field 9 case 3 LAT open field, asymmetric inhomogenity Field 10 case 3 LAT wedged field asymmetric Inhomogenity Level II underpinning Level III Example fields
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 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
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 44
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 45 100 % = >95 %
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 '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'