Quality Assurance for Treatment Planning Systems

Transcription

1 Quality Assurance for Treatment Planning Systems PTCOG Educational Session May 19 th 2010 Oliver Jäkel Heidelberg Ion Beam Therapy Center and German Cancer Research Center, Heidelberg

2 Introduction Outline International recommendations; common sources of errors; vendor and user responsibility; legal aspects; risk analysis Framework of QA QA and QC; acceptance tests; commissioning; periodic QA; uncertainty, deviation and tolerance; documentation; Tools and Methods System verification; software checks; measurements; Monte Carlo algorithms; analysis of results; Typical test procedures Software and data base; data transfer; generation of control parameters; imaging QA; geometrical and dosimetrical tests on dose distributions; radiobiological issues; Conclusions Page 3 Oliver Jäkel Medical Physics

3 Fatal Errors in TP Introduction 621 mistakes in NY state : At average 2 mistakes contributing Page 4 Oliver Jäkel Medical Physics

4 Intro: Recommendations IAEA TRS No.430, 2004: Commissioning and Quality Assurance of Computerized Planning Systems for Radiation Treatment of Cancer IAEA-TECDOC-1540, 2007: Specification and Acceptance Testing of Radiotherapy Treatment Planning Systems IAEA-TECDOC-1583, 2008: Commissioning of Radiotherapy Treatment Planning Systems - Testing for Typical External Beam Treatment Techniques AAPM Report 55, TG 23: Radiation treatment planning dosimetry verification,1995 Van Dyk J et al. Commissioning and quality assurance of treatment planning computers. IJROBP 26, p261, 1993 Fraas B, et al. AAPM TG 53: Quality assurance for clinical radiotherapy treatment planning. Med. Phys. 25: p.1773, 1998 Jacky J, White CP, IJROBP 18:253.Testing a 3-D radiation therapy planning program (1990) Page 5 Oliver Jäkel Medical Physics

5 Intro: Common Sources of Error IAEA: Lessons Learned from Accidental Exposures in Radiotherapy, Safety Reports Series No. 17, IAEA, Vienna (2000). Inconsistent/incorrect basic data Insufficient understanding of TPS Incorrect calculation of open/wedged fields Calc. error after change of TP Confusion of fractional dose vs. total dose Misunderstanding of complex TP given verbally lack of documentation and verification Inadequate commissioning Insufficient understanding of the TPS Incomplete validation Lack of an independent check of the treatment plan Lack of effective procedures Most TP errors can be summarized by a lack of: Education, Verification, Documentation, Communication. Page 6 Oliver Jäkel Medical Physics

6 Intro: vendor responsibility Accurate specifications outlining system capabilities, algorithms (incl. capabilities and limitations) Detailed system documentation (system design, dose normalization, MU calculations) User training: (1) basic training (2) commissioning process (3) system management (4) implementation of a QA program Detailed information regarding software updates, program alterations Clear communication regarding bugs, error reporting Page 7 Oliver Jäkel Medical Physics

7 Intro: Intro: User legal responsibility aspects Define responsible physicist for supervision and management (incl. installation, acceptance, commissioning and QA) Implementation of acceptance, commissioning and QA process Record keeping associated with acceptance, commissioning, QA User training / staff education: clinical use of TPS and its output(!) Implementation, commissioning, QA of software upgrades incl. documentation Ongoing communication with the vendor regarding software bugs and updates Ongoing communication with the users of the output of the TPS esp. regarding limitations and bugs. Page 8 Oliver Jäkel Medical Physics

8 Intro: Legal Aspects of QA Intl. Recommendations (IAEA TecDoc 1040 QA in RT, ICRU) European directives (e.g. Medical Device Directive) AAPM (TG 24), ESTRO (Booklet No 4) National radiation protection regulation Guidelines for medical application of radiation National and International standards (ISO, IEC), e.g.: DIN : Quality management system in medical radiology Part 1: Radiotherapy IEC 62083: Medical electrical equipment - Requirements for the safety of radiotherapy treatment planning systems There are few detailed and hard requirements The user always has to define a specific QA program Page 9 Oliver Jäkel Medical Physics

9 Intro: Risk Analysis Identify, characterize, and assess potential risks Assess the vulnerability of critical elements to specific risks Quantify the risk (expected consequences of specific events) Prioritize risk reduction measures based on a strategy Probability F: Frequent IIa IIb III E: Probable IIa IIb D: Sometimes IIa C: hardly conceivable IIa IIb IIb B: very unlikely IIa IIa A: : inconceivable I None Irrelevant Small Critical Fatal Effects Page 10 Oliver Jäkel Medical Physics

10 Framework: QA and QC Quality assurance: All planned and systematic actions necessary to provide confidence that a product will satisfy given requirements for quality. Quality Control: The regulatory process through which the actual quality performance is measured, compared with existing standards, and the actions necessary to keep or regain conformance with the standards. The QC process: (a) the definition of a specification; (b) the measurement of performance associated with that specification; (c) the comparison of the measurement with the specification; (d) the possible action steps required if the measurement falls outside the specification. As part of step (d), one needs to define what is an acceptable deviation (a tolerance) from the known standard. Page 11 Oliver Jäkel Medical Physics

11 Framework: Implementation of a TPS Assessment of clinical needs Selection and purchase Installation Acceptance test Commissioning Training Clinical use Periodic and patient specific QA Page 12 Oliver Jäkel Medical Physics

12 Framework Acceptance test Assure that the specifications of a product and safety standards are fulfilled (radiation and electrical hazards) Commissioning Characterization of the equipment's performance over the whole range of possible operation following acceptance incl. the preparation of procedures, protocols, instructions, data for clinical service. It includes development of procedures and QC tests and training. Periodic QA Procedures which are performed regularly and which allow to assess, if the initial requirements are still fulfilled; may involve different procedures than during commissioning; Patient specific QA Procedures performed on patient specific treatment plan or equipment. Page 13 Oliver Jäkel Medical Physics

13 Framework: Uncertainty, deviation and tolerance Deviation: Difference between a measured or calculated value and a reference value. Deviations will depend on many factors: position in the beam, complexity of phantom and treatment plan dose calculation algorithm Tolerance: Range of acceptability beyond which corrective action is required; Tolerances are always specific for a certain facility and application. Uncertainty: The uncertainty of a measured value has to be included in the tolerance or (preferred) may be added later; Typically: accuracy of algorithms, beam delivery, beam properties, CT data, dosimetry Error: Deviation of a quantity obtained through an incorrect procedure; A result maybe within the tolerance although an error was made Page 14 Oliver Jäkel Medical Physics

14 Sources of uncertainty Dose measurements (Ion chamber, film, etc) Setup of phantoms Beam delivery (esp. in scanning, field homogeneity, stability) Dose calculation algorithm Approximations of the beam model Geometric parameters (acc. of readings, instruments) Differences between commissioning and constancy checks Example: How to separate beam delivery from TPS: Commissioning: Measure dose and compare with TP-dose Defines reference for TP and Dosimetry TP Periodic checks: Repeat calculation & compare w. safety copy Dosimrtry check: Repeat measurement & compare w. old data Page 15 Oliver Jäkel Medical Physics

15 Tools and Methods: Steps in QC 1. Definition of the specifications (performance and test characteristics) 2. Definition of tolerances (incl. uncertainties) 3. Definition of tests via - System verification - Software checks - Dosimetric measurements - Monte Carlo simulations 4. Performing tests and Comparison w. specs 5. Possible Action steps if outside tolerance Page 16 Oliver Jäkel Medical Physics

16 MC versus TPS dose for passive MGH Paganetti et al, Phys. Med. Biol. 53, 2008 G4 Monte Carlo XiO 1 Gy(RBE) 3 Gy(RBE) 5 Gy(RBE) 7 Gy(RBE) 9 Gy(RBE) 11 Gy(RBE) 13 Gy(RBE) 15 Gy(RBE) 17 Gy(RBE) Range Findings (29 fields): differences between TPS (PB-Alg.) and MC especially near the end of range + difference dose-to-water vs. dose-to-tissue Page 17 Oliver Jäkel Medical Physics

17 MC vs. TPS for lateral inhomogeneity Water slab TPS plan FLUKA recalculation of treatment plan Bone slab Bone slab Courtesy of F. Sommerer et al, HIT Water slab Underdosage up to ~20%, consistent with dosimetric finding in water phantom Page 1 Oliver Jäkel Medical Physics

18 MC for individual treatment plans TPS (TRiP) Test proton plan: TPS (with input FLUKA-generated Database) vs MC FLUKA Page 2 Oliver Jäkel Medical Physics Courtesy of Parodi K., Sommerer F., Unholtz D., Brons S.

19 Cautions Monte Carlo simulations are extremely powerful They will immediately show differences as compared to TPS A Monte Carlo is not automatically giving correct results, although its algorithms may be more accurate than the TPS Monte Carlo requires much more information as input (cross sections, HU-LUT for all materials) QA for a Monte Carlo may be very complicated: - Documentation of the Code, User Manual - Version control and change management - Benchmarking of code - Control of input parameters (cross sections etc.) Very few (if any) certified codes for p-rt exists! Clinical decisions should drawn very carefully! Page 18 Oliver Jäkel Medical Physics

20 Examples of Test HIT Software & data base: Versioning, data base, data transfer, PACS- archive Machine interface & control parameters Calc. energies, ranges, field size, spot positions, fluence optimization Imaging QA Data transfer, HU-checks, geometrical image checks (distortions, scales, contrast), stereotactic tests, DRR Geometrical tests on dose distributions Field size, depth modulation, lateral and distal gradients Dosimetrical tests on dose distributions Homogeneous phantom (water, different angles) Depth inhomogeneities (slab phantom) Lateral inhomogeneities (slabs) Irregular inhom. Phantom (Alderson) Radiobiological issues Check p-rbe, recalculate standard plans Page 19 Oliver Jäkel Medical Physics

21 Plans of different complexity Defined measurement positions: 1 High Dose 2 Plateau 3 Lateral Gradient 4 Distal Gradient HIT: Dosimetric tests in a water phantom Regular Target: Max. dev i,max : 5% Mean. dev : 3% max *Relative to maximum dose Courtesy of S. Klemm Page 20 Oliver Jäkel Medical Physics

22 Checks on the data base for treatment planning ddd 1 HIT To measure or not to measure? Page 3 Oliver Jäkel Medical Physics TPS: - check if input=output - check machine control file - check consistency Beam delivery: measure! 3

23 Empirical range calculation from CT numbers Tissue equivalent phantoms Real tissue measurements Range relative to water CT number Page 4 Oliver Jäkel Medical Physics

24 Imaging-QA: Possible distortions of CT numbers Filter: AH50 AH90 Contrast agent in CT mean shift (25 pat.): 18 HU max shifts: 36 HU Errors in range < 1.6 % Reconstruction filters redistribution of HU numbers Errors in range < 3 % Dedicated imaging protocols and imaging QA required Page 5 Oliver Jäkel Medical Physics

25 PET for Range verification? Patient with Chondrosarcoma of skull base PET-Measurement Dose distribution carbon ions PET is not routinely used for formal QA at GSI/HIT Page 6 Oliver Jäkel Medical Physics

26 Field geometry: IC in water vs. Films Commissioing: Ion chambers Lateral Measurement lateral right TPS lateral right Measurement lateral left TPS lateral left Periodic QA: films D/D(max) lateral position in mm Courtesy of B. Ackermann Page 21 Oliver Jäkel Medical Physics

27 Dosimetric Checks of dose calculation Measurement equipment for commissioning Water Phantom PTW Freiburg 24 PinPoint chamber array connected to a MP3 controller 2 12-channel Multidos dosimeters Page 7 Oliver Jäkel Medical Physics

28 Dosimetric Verification of treatment plans for commissioing and patient specific QA Data-acquisition in the TPS Vx Verification Mode in TPS (Syngo PT Planning) Dose calculation in water for each PinPoint-Chamber Calculated dose [cgy] Gradient information [Gy/mm] Page 8 Oliver Jäkel Medical Physics

29 Tolerance for dose HIT Regular Target: Max. dev. i,max < 5% Mean. Dev. : < 3% max Irregular/complex Target: Max. dev: i,max < 7% Mean. dev: < 5 % max 2 1 Tolerances include dosimetric uncertainties! Page 11 Oliver Jäkel Medical Physics

30 MC application to active beam HIT FLUKA dose calculations of scanned fields for comparison with measurements and TPS calculation to support TPS-commissioning Protons Meas.: ICs in water phantom + data acquisition system from C. Karger (DKFZ) eye view Along depth Along depth FLUKA: ~ 10 8 p out of irradiated Parodi, Mairani, Brons, HIT to be published Page 22 Oliver Jäkel Medical Physics

31 Patient Plan Verification: C-12 Page 23 Oliver Jäkel Medical Physics

32 Radiobiological QA: Verification with cell samples Mitaroff A et al, Rad. Env. Biophys Measurements for validation of the model and TPS. No biological QA routinely used for formal QA at HIT. Page 12 Oliver Jäkel Medical Physics

33 MC for biological dose GSI / HIT FLUKA interfaced during runtime with the Local-Effect-Model (M. Scholz et al, GSI) used by GSI / HIT - TPS (TRiP98): biological planning and optimization for CHO cells FLUKA-LEM: forward calculation of the optimized plan FLUKA TRiP98 Exp data Exp. Data and TPS calculations: Krämer et al, PMB 48 (2003) 2063 MC Calculations: A. Mairani et al, Book of Abstract EW-MCTP, Cardiff, 2009; submitted to PMB Page 13 Oliver Jäkel Medical Physics

34 Radiobiological HIT No real biological QA Test only constancy of algorithms Benchmark of new algorithm vs. old algorithm Check input in data base Courtesy of C. Karger Page 24 Oliver Jäkel Medical Physics

35 Conclusion Carefully analyze the clinical needs Write down performance characteristics Define test characteristics, tolerances, actions Define how to test (SOPs for commissioing and periodic QA) Analyze uncertainties (SOP) Document all results Summarize findings for the users Page 25 Oliver Jäkel Medical Physics

36 Always think of the unexpected! Page 15 Oliver Jäkel Medical Physics