The application of error reduction QA philosophy in HDR brachytherapy

Transcription

1 The application of error reduction QA philosophy in HDR brachytherapy Bruce Thomadsen University of Wisconsin - Madison

2 Learning Objectives Learning objectives: To understand 1. The problem with the current QA paradigm, 2. The advantage of the new paradigm, and 3. The application to HDR Brachytherapy

3 The Problem with the Old Paradigm What is the old paradigm? If you can check it, check it!

4 Regulations QM Guidance Derives from recommendations (below). Machine specs from the FDA. Regs on users comes from NRC, if using radionuclides. User regs used to be spotty, based on the most recent incident. Now, the new CRCPD Suggested Regulations incorporate professional guidelines.

5 QA Guidance NCRP - often a little late ACR - very sketchy ACMP - seem to be out of the business IAEA - very much derivative of other guidance documents, except for two new reports.(iaea (IAEA-TECDOC 1494, Case studies in the application of probabilistic safety assessment techniques to radiation sources; The other is not yet released.)

6 Mostly, QM from AAPM Many Reports from the AAPM (American Association of Physicists in Medicine) discuss QM Frequently, the reports have been incorporated into laws.

7 QA Guidance The main source currently is AAPM reports. Report 13: Physical Aspects of Quality Assurance in Radiation Therapy (1984)Radiation Therapy Committee Task Group #24, with contribution from Task Group #22; 63 pp. Report 24: Radiotherapy Portal Imaging Quality (1987) Radiation Therapy Committee Task Group #28; 29 pp Report 41: Remote Afterloading Technology (1993) Remote Afterloading Technology Task Group #41; 107 pp. Report 46: Comprehensive QA for Radiation Oncology (1994) Radiation Therapy Committee Task Group #40; 37 pp. Report 47: AAPM Code of Practice for Radiotherapy Accelerators (1994) Radiation Therapy Task Group #45; 37 pp. Report 56: Medical Accelerator Safety Considerations (1993) Radiation Therapy Committee Task Group #35; 15 pp. Report 59: Code of Practice for Brachytherapy Physics (1997) Radiation Therapy Committee Task Group #56; 42 pp. Report 61: High Dose-Rate Brachytherapy Treatment Delivery (1998) Radiation Therapy Committee Task Group #59; 29 pp. Report 62: Quality Assurance for Clinical Radiotherapy Treatment Planning (1998) Radiation Therapy Committee Task Group #53; 57 pp. Report 83: Quality assurance for computed-tomography simulators and the computedtomography-simulation process (2003); 31pp. Radiation Therapy Committee Task Group #66

8 And of those Reports Okay, the first three are archaic. This list doesn t t count dosimetry or procedure reports. But that leaves a bunch. So far, the TG 40 and TG 45 have frequently been carved in stone in regulations. For brachytherapy, Reports 59 (TG 56) and 61 (TG 59) are of interest in particular.

9 The Problem The reports, except for TG 53 (QA for Computer Planning Systems) are prescriptive. (TG 53 is comprehensive, and only partly prescriptive.) As noted, the premise: If it can be checked, check it. That is everything. Almost no facility has the personnel to completely do it all. And, the QA may not prevent errors!

10 Another Problem: The reports can t t keep up Since the reports, new technologies, such as 3D conformal, IMRT, 4D motion-correction systems, Image-based localization all have come on line. All of these have QM needs. What s s a physicist to do?

11 The New Paradigm The new paradigm approaches the problem differently, in an organized way. Map out (understand) the process Determine the potential failures, with particular attention to human failures. Map out the potential failures along with protections. See when to interrupt the propagation of failures.

12 TG 100 AAPM created TG 100 to update TG 40 for new modalities. It soon became evident that this was making a hard situation even worse. The TG decided to take a different tack. The new approach would be based on risk assessment.

13 IAEA Report One of the recent IAEA reports looked at risk assessment and concluded that most effort went into assessing equipment, while most events stemmed from human errors.

14 Human and Mechanical Failures Even when events have followed mechanical failures, the human response has lead to the injuries. Witness that the same failure could happen in two facilities leading to an event in one and no problem in the other (for example an Omnitron source breaking off in a patient).

15 Risk Assessment Regulations lately like to be risk based or risk informed. Unfortunately, the regulations have little to base their risk on except when something has happened, that is, if it has happened in the past, it must have a high risk. There are techniques for assessing risk, and TG 100 is using some of them.

16 Process Map or Tree The goal is to understand the process and how all the steps interrelate. Many ways to map the process. One common mapping is a Process Tree.

17 LDR Brachytherapy Process Tree 1: Placement followed by dosimetry Procedures leading to an LDR Patient treatment Application Measurement Calibration 2 correct target Localization Applicator Correct anatomy Correct applicator placement Identification Correct selection factors strength date Calculation of strength 1 Calibration factors Reading Placement in well Set chamber Set source 1 Entering data in computer Reconstruction Dummies Image quality Record Geometry 1 Record Placement Applicator fixation Setup Correct films Image quality Interpretation Identification Dose / time calculation Hardware operation Software operation Procedure Fiducials Anatomy Per algorithm Targeting 3 source strength Planning quality assurance Identity Dummies Geometry Per localization factors Correctness Data entry 1 Duration calculation Optimization 2 Specification clinical Protocol stage Anatomic information Limitations of algorithms Dosimetry calculation 8 3 patient data input Source preparation Satisfaction Source loading Consistence Prescription 10 Completion 2 Source selection Insertion in carrier Treatment termination Patient identification 1 source integrity Applicator check 1 Source verification 10 Source loading 4 Source fixation 1 Source count 1 Time recording 1 Removal calculation Monitoring Dose Other Tx information information 1 Post Tx monitoring 1 Source removal Removal preparation Removal time verification 9 Successful Treatment treatment duration executed Recording Emergency response Radiation survey The numbers give the failures at that location in a study

18 EPID imaging For localization 17 3x7x4=84 Day 1 imaging verification Place patient on table 3x7x4=84 4x5x5=100 Select beam in Align all Align mold marks b 4x5x5=100 record & verify marks 2x7x2=28 3x7x4=84 Pt in mold Image 4x5x5=100 3x7x4=84 a Set Make AP image 1x2x1=2 Register beam Verify clearance parameters Make Set Set gantry outline c plan and achievability 4x5x5=100 exposure mu Set field size 2x5x2=20 1x2x1=2 3x5x1=15 Set machine 1x2x1=2 Make lateral image 1x2x1=2 Repeat for Make Set Set gantry b each beam exposure mu Set machine Verify images are adequate 1x2x1=2 Verify beam outlines Approve patient position Determine patient Shifts and rotations 2x5x2=20 Reimage if necessary Register EPID and pseudoradiograph 4x5x5=100 a Approve treatment if good 3x6x4=108 Review beam images 2x5x4=40 3x6x4=108 4x5x5=100 Verify patient setup Load Pseudoradiograph 4x5x5=100 Load EPID 2x4x3=24 Review setup images 2x6x4=48 Approval to treat These numbers for this step in IMRT are from an FMEA

19 TG 100 and FMEA TG 100 is performing a FMEA for IMRT and HDR brachytherapy. It s s taking a while. Here is a sample:

20 Sample FMEA Topic Step Specify images for target and structure delineation, etc Potential Failure Modes Specify use of incorrect image set Viz.; wrong phase of 4D CT selected for planning; wrong MR for target volume delineation Potential Cause of Failure Ignorance of available imaging studies Miscommunication Ambiguous labeling of image sets Inadequate training Potential Effects of Failure Wrong anatomical model (leading to systematic geometric and dosimetric errors) O S D RPN Comments D CT gating. Software error User error Specify protocol for delineating target and structure Incomplete/ incorrect list of specified structures and corresponding image sets Ignorance of available imaging studies Miscommunication Ambiguous labeling of image sets Wrong anatomical model (leading to systematic geometric and dosimetric errors) Lack of explicit protocol User error

21 Risk Probability Number O = likelihood of O S D RPN occurrence; S = severity of the effects of the failure; D = likelihood failure would go undetected. RPN = risk probability number = product of OxSxD. Values for O, S, and D between 1 and 10, (1 = low danger, 10 = high). In industry, RPN <125, little concern, however, in medicine, RPN > 20 might warrant some consideration.

22 Hazard Going through the exercise makes one wonder how we ever get a case right. It also takes a long time. But it helps direct resources to the greatest hazard.

23 Fault Trees From the FMEA, construct fault trees. They start with a failure mode and work backwards asking, what could have caused the failure? Then ask, what could have caused that failure? And you keep asking until you reach the end of your universe (where you no longer can control the causes).

24 HDR Fault Tree 0 Fractionation failure or 0 0 Prescription error Accounting error A B Go to Page 2 Go to Page 2 0 Wrong applicator used C Go to Page 2 44/44 Deviation from adequate treatment or 43/44 Wrong dose distribution or site or Treatment planning failure 13/44 and 13/44 13/44 3/44 Error in treatment planning Verification error Applicator positioning error D G Go to Page 3 Go to Page 6 30/44 Treatment implementation failure or 2/44 Applicator connection error H Go to Page 7 1/44 Wrong patient selected 21/44 Treatment programming failure I Go to Page 7 1/44 Wrong patient treated and 4/44 Treatment delivery error J Go to Page 8 1/44 Failure to identify patient 0 Treatment terminated prematurely L Go to Page 10 Page 1

25 Incompatible factors for calibration and dose calculation Wrong or incompatible units or Wrong chart referenced Physician's error Some Wrong patient's data used Incorrect data transfer or Error in transfer (transcription) Data transposition Parts of 1/44 2/44 Incorrect data entry Wrong dose or Interpretation error Incorrect entry 2/44 Physician's error the Tree 7/44 F Dose calculation error or 2/44 2/44 Wrong location of dose distribution Dose specification to wrong points Wrong dwell positions activated or or Inaccurate source position entry QM failure Entry error Inappropriate marker 2/44 are Broad Incorrect dwell times entered (manual, not optimized) Marker in wrong position Incorrect shape of dose distribution (incorrect optimization) Inconsistent step size or Error in specification Incorrect marker used Programming error Algorithm error and Acceptance testing error Software error or Software version incompatibility and File corruption QM failure Page 5 Corrupt file

26 Some Parts Wrong units of the Tree Calibration error or Measurement error are Deep Wrong calibration and Failure of verification Calculation error Error in data entry 10/44 E Dosimetry Error or 3/44 7/44 Source strength error Dose calculation error F or Go to Page 5 3/44 Wrong source data Wrong data (wrong decay factor) and and 3/44 3/44 Erroneous strength for source data Failure of verification Wrong data format (US/Euro) or 3/44 Failure to enter or alter data (unit default) Wrong source in device Discrepency in strength between device and planning system Incorrect entry Page 4

27 What the Fault Tree Tells The fault tree shows how failures propagate to become an event. Interrupting the propagation path can (may) stop the failure from propagating. Quality management tools act to intercept the failure.

28 Quality Management QM consists of many parts (or should). Two parts we will discuss today are quality control (QC) and quality assurance (QA). QC forces quality on the procedure; QA demonstrates a level of quality. A diagram can help understand the difference.

29 Organizational Difference between QA and QC Input 1 QC Input 2 Input 3 QC QC Process QA Input 4 QC

30 In General QC makes sure the inputs to a process are correct before they enter. QA looks at the output and evaluates if it is correct. Of course, most processes outputs become inputs for other processes, so one process s QA becomes another s s QC.

31 Example: Calculation Error Tree with QM Error in Input Data Error in QC Error in Data Entry Error in Calculation Error in QA Error in QC Error in Calculational Algorithm Error in QC Error in Prescription Error in QC

32 Priorities for QM Tools Forcing functions and constraints Interlock Barriers Computerized order entry with feedbac k Automation and computerization Bar codes Automate monitoring Computerized verification Computerized order entry Protocols, standards, and information Check off forms Establishing Protocol / Clarify Protocol Alarms Labels Signs Reduce s imilarity Independent double check systems and other redundancies Redundant mea surement Independent review Operational Checks Comparison with standards Increase monitoring Add status check Acceptance te st Rules and policies External Audit Internal Audit Priority Establishing / Clarify Communication Line Staffing Better Scheduling Mandatory Pauses Repair PMI (Preventive Maintenance In spection) Establish and Perform QC and QA (Hardware and Software) Education and Information Training Experience Instruction Environment (Environmental Controls) Sound Control (Environmental Controls) Cleaning (Environmental Controls) Neatening (Environmental Controls) Isolation (Environmental Controls) Visual Control Environmental Design [Rank the effectiveness of tools based on the suggestion of ISMP]

33 Frequency for QM QC every time a procedure is performed QA with a period such that the worse possible conditions for which the QA screens would produce no harm.

34 Comparison of QA and QC QC procedures often require more resources than QA (to cover large numbers of inputs) but failures detected by QC less costly to correct. Relying on QA can add time to a procedure since failures detected often require repeating the process. QA and QC work best together. If your QA picks up a lot of errors, you need to move resources to the QC; If your QA does not pick up occasional errors, it may be time to eliminate it.

35 Application of the Principle: Annual Linac Calibration The annual calibration takes several days to complete. If everything checks out, the effort was mostly wasted that is, it could have been spent checking things with a higher likelihood of failure. If some problem was found, how long had it been wrong and shouldn t t it have been found earlier?

36 Application to HDR Brachytherapy Recognize that all events have been due to human performance failures. Many have been initiated or complicated by machine failures.

37 HDR Machine Failure Examples Omnitron source breaking off in a patient Developed into an event in one facility but not in another.

38 HDR Unit Problems Leading to Human Failure Treatment program card writer malfunction led to manual programming error.

39 Programming Error During the programming, the physicist entered 260 second for one dwell position instead of 26. Seconds = Calculator HDR Unit * # Phone

40 HDR Unit Problems Leading to Human Failure Treatment program card writer malfunction led to manual programming error. Change in length of source and transfer tubes led to delivering the treatment to the wrong location. Default setting for the length caused many treatments to the wrong location.

41 HDR QM - Commissioning Commissioning Measure lengths and compatibility of transfer tubes and applicators. Test the x-ray x markers and distance rulers. Know where the first dwell position lies in all applicators and the appropriate lengths to use (particularly for interstitial cases). Make sure that the units for source strength are what will be entered.

42 HDR QM Daily Unit Checks Pay particularly attention to those aspects that: Have had reported problems in the past, or Would likely lead to an event if a failure occurred. Low priority items are those that never have caused a problem, or if they fail, would have little impact.

43 HDR QM Daily Unit Checks High Priority Distance Emergency off Door interrupt Transit time Radiation detectors Low Priority Calibration Treatment Interrupt.

44 HDR QM Source Change High Priority Those high-priority checks from the daily QA, Calibration of the source, Entry of the source strength into computers, and Check of the x-ray x markers for damage. Low Priority (required, however) Radiation survey around the room, Transfer tube length measurement (particularly if use long markers).

45 Source Change QA The calibration of the source and the entry of the calibration into the treatment planning and treatment unit computers should be checked since they affect all patients. A review by someone else forms the best check.

46 HDR QM Per Patient Almost all events occur in this arena. Items to check Applicator function, The treatment plant, The treatment unit program, Connections between the applicator and the unit. The treatment plan is best checked by someone other than the person who generated it.

47 Things to Check on a Plan Things that would affect the treatment The prescribed is filled: Correct dose to the Correct location Shape of the dose distribution achieves desire Prescribed isodose surface covers target volume Dose distribution has appropriate homogeneity Critical organs remain below tolerance Plan correctly transferred to program Plan contains no errors

48 Independent Verification Key word: Independent! Can be a second person Can it be running on a second computer? Yes, if the input is completely new. No, it the information from the first is simply entered into the second (this just checks that the algorithms work the same - something that should have been done at acceptance testing). The errors we are looking for are in the inputs, not in the computer s s calculation.

49 Check Treatment Times for Consistency There are several methods in the literature: see Thomadsen, Achieving Quality in Brachytherapy. Das has developed a set of checks for any application: Das RK, Bradley KA, Nelson IA, Patel R, Thomadsen BR. Quality assurance of treatment plans for interstitial and intracavitary high-dose dose-rate brachytherapy. Brachytherapy. 5(1):56-60, 60, 2006

50 Position Verification Radiographs with dummies that include the transfer tubes will verify source positions.

51 Applying the Approach A study applying the new paradigm looked at all reported HDR misadministrations. Some of the conclusions follow.

52 Findings Applying the Approach 1 1. Evaluation of a medical procedure using risk analysis provides insights. 2. Failure to consider human performance in the design of equipment led to a large fraction of the events reviewed. While the equipment per se did not fail, the design facilitated the operator to make mistakes that resulted in the erroneous treatments. Of particular danger were those situations where equipment malfunctions force operators to perform functions usually executed automatically by machines. Entry of data in terms of units other than those expected by a computer system also accounted for several events.

53 Findings Applying the Approach 2 3. HDR brachytherapy events tended to happen most with actions having the least time available. 4. Many events followed the failure of persons involved to detect that the situation was abnormal, often even though many indications pointed to that fact. 5. Once identified, the response often included actions appropriate for normal conditions, but inappropriate for the conditions of the event.

54 Findings Applying the Approach 3 6. Lack of training (to the point that persons involved understand principles) and 7. Lack of procedures covering unusual conditions likely to arise (and sometimes, just routine procedures) frequently contributed to events. 8. New procedures, or new persons joining a case in the middle also present a hazard.

55 Findings Applying the Approach 4 9. Most of the events suffered from ineffectual verification procedures. For the most part, improved quality management would serve to interrupt the propagation of errors by individuals into patient events. 10. Important contributors to events are: a) Rushing due to lack of staffing or equipment problems b) Insufficient information

56 Conclusion We can no longer manage quality by doing everything we can think of. We have to assess risk and pick and choose. The techniques are not hard, but require training and practice.